ult/Using_Linux_Tools.rst
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Introducing Linux
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=================
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(Attribution : A significant chunk of the content under this section is based on data from Wikipedia and the Linux Documentation Project)
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Linux (usually pronounced ˈlɪnəks') is a generic term referring to Unix-like computer operating systems based on the Linux kernel, where a kernel is the intermediate layer between the hardware and the applications. The kernel is, on an abstract level, the core of (most) operating systems, that manages the various system resources. The development of the Linux OS is considered the basis for Free and Open Source Software (FOSS) collaboration since typically the underlying source code can be used, modified freely, and redistributed by anyone under the terms of the GNU (a recursive acronym for "GNU's Not Unix!") Global Public License (GPL) and other free software licences. This freedom to access and reuse various components of a system, is one of the primary reasons for the popularity of Linux.
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Linux is installed on a variety of computer hardware, that include mobile phones, embedded devices and supercomputers, but is infamous for its use in servers.
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The name "Linux"  comes from the Linux kernel, originally written in 1991 by Linus Torvalds. The rest of the system usually comprises components such as the Apache HTTP Server, the X Window System, the GNOME and KDE desktop environments, and utilities and libraries from the GNU Project (announced in 1983 by Richard Stallman). Commonly-used applications with desktop Linux systems include the Mozilla Firefox web-browser and the OpenOffice.org office application suite. The GNU contribution is the basis for the Free Software Foundation's preferred name GNU/Linux. The kernel's mascot is a penguin named "Tux". Mozilla Firefox and OpenOffice.org are open-source projects which can be run on most Operating Systems, including proprietary ones.
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Historical Background
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Events leading to the creation
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- The Unix operating system was developed in the 1960s and released for public use in 1970. Its accessibility and portability caused it to be widely adopted, copied and modified by academic institutions and businesses. Its design became influential to authors of other systems. Other free operating systems include the Berkeley Software Distribution (BSD), developed at the University of California at Berkeley, and MINIX which was released by Andrew S. Tanenbaum. The development and adoption of BSD and MINIX were limited due to various reasons, and this lack of a widely-adopted and free kernel triggered Linus Torvalds into starting his project.
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- In 1983, Richard Stallman started the GNU project with the goal of creating a free UNIX-like operating system. As part of this work, he wrote the GNU General Public License (GPL). By the early 1990s there was almost enough available software to create a full operating system. However, the GNU kernel, called Hurd, failed to attract enough attention from developers leaving GNU incomplete.
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The Creation of Linux
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In 1991, Linus Torvalds began a project at the University of Helsinki that later became the Linux kernel. It was initially a terminal (command-line) emulator, which Torvalds used to access the large UNIX servers of the university. He wrote the program targeting just the hardware he was using and independent of an operating system because he wanted to use the functions of his computer with an 80386 processor. Development was done on Minix using the GNU C compiler. This application is still the main choice for compiling Linux today (although the code can be built with other compilers, such as the Intel C Compiler).
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Torvalds continues to direct the development of the kernel. Stallman heads the Free Software Foundation, which in turn supports the GNU components. Finally, individuals and corporations develop third-party non-GNU components, which constitute a vast body of work and including kernel modules, and user applications and libraries. Linux vendors and communities combine and distribute the kernel, GNU components, and non-GNU components, with additional package management software in the form of Linux distributions.
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Design and Implications
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A Linux-based system is a modular Unix-like operating system, deriving much of its basic design from principles established in Unix earlier. Such a system uses a monolithic kernel, called the Linux kernel, which handles process control, networking, and peripheral and file system access. Device drivers are integrated directly with the kernel. Separate projects that interface with the kernel provide much of the system's higher-level functionality. The GNU userland is an important part of most Linux-based systems, providing the most common implementation of the C library, a popular shell, and many of the common Unix tools which carry out many basic operating system tasks. The graphical user interface (or GUI) used by most Linux systems is based on the "X Window System".
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User Interface
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Users can control a Linux-based system through a command line interface (or CLI), a graphical user interface (or GUI), or through controls attached to the associated hardware (this is common for embedded systems). For desktop systems, the default mode is usually the GUI. On desktop machines, "KDE", "GNOME" and "Xfce" are the most popular user interfaces,though a variety of additional user interfaces exist. Most popular user interfaces run on top of the "X Window System" (or X), which enables a graphical application running on one machine to be displayed and controlled from another in a network.
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A Linux system also provides a CLI of some sort through a shell, which is the traditional way of interacting with a Unix system. A Linux distribution specialized for servers may use the CLI as its only interface. A “headless system” (system run without even a monitor) can be controlled by the command line via a remote-control protocol such as SSH or telnet. The CLI is particularly suited for automation of repetitive or delayed tasks, and provides very simple inter-process communication. A graphical terminal emulator program is often used to access the CLI from a Linux desktop.
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Development
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The primary difference between Linux and many other popular contemporary operating systems is that the Linux kernel and other components are free and open source software. Linux is not the only such operating system, although it is by far the most widely used. Some free and open source software licenses are based on the principle of "copyleft", a kind of reciprocity: any work derived from a copyleft piece of software must also be copyleft itself. The most common free software license, the GNU GPL, is a form of copyleft, and is used for the Linux kernel and many of the components from the GNU project.
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Linux based distributions are intended by developers for interoperability with other operating systems and established computing standards. Linux systems adhere to POSIX, SUS, ISO and ANSI standards where possible, although to date only one Linux distribution has been POSIX.1 certified, Linux-FT.Free software projects, although developed in a collaborative fashion, are often produced independently of each other. The fact that the software licenses explicitly permit redistribution, however, provides a basis for larger scale projects that collect the software produced by stand-alone projects and make it available all at once in the form of a Linux distribution.
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A Linux distribution, commonly called a "distro", is a project that manages a remote collection of system software and application software packages available for download and installation through a network connection. This allows the user to adapt the operating system to his/her specific needs. Distributions are maintained by individuals, loose-knit teams, volunteer organizations, and commercial entities. A distribution can be installed using a CD that contains distribution-specific software for initial system installation and configuration. A package manager such as Synaptic or YAST allows later package upgrades and installations. A distribution is responsible for the default configuration of the installed Linux kernel, general system security, and more generally integration of the different software packages into a coherent whole.
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Community
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A distribution is largely driven by its developer and user communities. Some vendors develop and fund their distributions on a volunteer basis. Examples include Debian and the Debian-based, Ubuntu. Others maintain a community version of their commercial distributions, as Red Hat does with Fedora.
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In many cities and regions, local associations known as Linux Users Groups (LUGs) seek to promote their preferred distribution and by extension free software. They hold meetings and provide free demonstrations, training, technical support, and operating system installation to new users. Many Internet communities also provide support to Linux users and developers. Most distributions and free software / open source projects have IRC (Internet Relay Chat) chatrooms or newsgroups. Online forums are another means for support. Linux distributions host mailing lists; commonly there will be a specific topic such as usage or development for a given list. All these can be found simply by running an appropriate search on Google.
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Although Linux distributions are generally available without charge, several large corporations sell, support, and contribute to the development of the components of the system and of free software. These include Dell, IBM, HP, Oracle, Sun Microsystems, Novell, Nokia. A number of corporations, notably Red Hat, have built their entire business around Linux distributions.
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Can I make a profit out of running a business involving Linux?
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The answer is, "Yes!". The free software licenses, on which the various software packages of a distribution built on the Linux kernel are based, explicitly accommodate and encourage commercialization; the relationship between a Linux distribution as a whole and individual vendors may be seen as symbiotic. One common business model of commercial suppliers is charging for support, especially for business users. A number of companies also offer a specialized business version of their distribution, which adds proprietary support packages and tools to administer higher numbers of installations or to simplify administrative tasks. Another business model is to give away the software in order to sell hardware. Examples of corporations that are extensively (and sometimes exclusively) open-source and Linux-powered , with successful revenue generation models involving these, are Google, SUN, Mozilla, etc.
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Programming on Linux
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Most Linux distributions support dozens of programming languages. The most common collection of utilities for building both Linux applications and operating system programs is found within the GNU toolchain, which includes the GNU Compiler Collection (GCC) and the GNU build system. Amongst others, GCC provides compilers for Ada, C, C++, Java, and Fortran. The Linux kernel itself is written to be compiled with GCC. Proprietary compilers for Linux include the Intel C++ Compiler, Sun Studio, and IBM XL C/C++ Compiler.
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Most distributions also include support for PHP, Perl, Ruby, Python and other dynamic languages. Examples of languages that are less common, but still supported, are C# via the Mono project, sponsored by Novell, and Scheme. A number of Java Virtual Machines and development kits run on Linux, including the original Sun Microsystems JVM (HotSpot), and IBM's J2SE RE, as well as many open-source projects like Kaffe.
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The two main frameworks for developing graphical applications are those of GNOME and KDE. These projects are based on the GTK+ and Qt widget toolkits, respectively, which can also be used independently of the larger framework. Both support a wide variety of languages. There are a number of Integrated Development Environments (IDEs) available including Anjuta, Code::Blocks, Eclipse, KDevelop, Lazarus, MonoDevelop, NetBeans, and Omnis Studio while the long-established editors Vim and Emacs remain popular.
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Reasons for Using Linux
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- Linux is free:
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As in "free beer". Linux can be downloaded in its entirety from the Internet completely for free. No registration fees, no costs per user, free updates, and freely available source code in case you want to change the behavior of your system.
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Most of all, Linux is free as in "free speech":
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The license commonly used is the GNU Public License (GPL). The license says that anybody who may want to do so, has the right to change Linux and eventually to redistribute a changed version, on the one condition that the code is still available after redistribution. In practice, you are free to grab a kernel image and sell the new code, as long as your customers can still have a copy of that code.
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- Linux is portable to any hardware platform:
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A vendor, who wants to sell a new type of computer and who does not know what kind of OS his/her new machine will run, can take a Linux kernel and make it work on his/her hardware, because documentation related to this activity is freely available.
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- Linux was made to keep on running:
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As with UNIX, a Linux system expects to run without rebooting all the time. That is why a lot of tasks are being executed at night or scheduled automatically for other times, resulting in higher availability during busier periods and a more balanced use of the hardware. This property allows for Linux to be applicable to environments where people do not have the time or the possibility to control their systems constantly.
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- Linux is secure and versatile:
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The security model used in Linux is based on the UNIX idea of security, which is known to be robust and of proven quality. But Linux is not only safe from attacks from the Internet: it will adapt equally to other situations, utilizing the same high standards for security.
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- Linux is scalable:
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From a Palmtop with 2 MB of memory to a petabyte storage cluster with hundreds of nodes: add or remove the appropriate packages and Linux fits all. One does not need a supercomputer anymore,because you can use Linux to do big things using the building blocks provided with the system. If one wants to do little things, such as making an operating system for an embedded processor or just recycling your old 486, Linux will do that as well.
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- The Linux OS and Linux applications have very short debug−times:
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Because Linux has been developed and tested by thousands of people, both errors and people to fix them are found very quickly. It often happens that there are only a couple of hours between discovery and fixing of a bug.
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Getting Started
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================
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Logging in, activating the user interface and logging out
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----------------------------------------------------------
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In order to work on a Linux system directly, one needs to provide a user name and password. You always need to authenticate to the system. Most PC−based Linux systems have two basic modes for a system to run in: either quick and clean in text console mode,which includes with mouse, multitasking and multi−user features, or in graphical console mode, which looks better but eats more system resources.
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Graphical Mode
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~~~~~~~~~~~~~~
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This is the default nowadays on most desktop computers. You know you will be connecting to the system using graphical mode when you are first asked for your user name, and then to type your password.
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To log in, make sure the mouse pointer is in the login window, provide your user name and password to the system and click *OK* or press *Enter*.
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It is generally considered a bad idea to connect (graphically) using the root user name, the system adminstrator's account, since the use of graphics includes running a lot of extra programs, in root's case with a lot of extra permissions. To keep all risks as low as possible, use a normal user account to connect graphically. But there are enough risks to keep this in mind as a general advice, for all use of the root account: only log in as root when extra privileges are required.
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After entering your user name/password combination, it can take a little while before the graphical environment is started, depending on the CPU speed of your computer, on the software you use and on your personal settings.
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To continue, you will need to open a *terminal window* or *xterm* for short (X being the name for the underlying software supporting the graphical environment). This program can be found in the *Applications−>Utilities->System Tools* or *Internet menu*, depending on what window manager you are using. There might be icons that you can use as a shortcut to get an *xterm* window as well, and clicking the right mouse button on the desktop background will usually present you with a menu containing a terminal window application.
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While browsing the menus, you will notice that a lot of things can be done without entering commands via the keyboard. For most users, the good old point−n−click method of dealing with the computer will do. But for those who want to enter the "heart" of the system, a tool stronger than a mouse will be required to handle the various tasks. This tool is the shell, and when in graphical mode, we activate our shell by opening a terminal window.
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A terminal window should always show a command prompt when you open one. This terminal shows a standard prompt, which displays the user's login name, and the current working directory, represented by the twiddle (~)
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Another common form for a prompt is this one:
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[user@host dir]
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In the above example, *user* will be your login name, *hosts* the name of the machine you are working on, and *dir* an indication of your current location in the file system. Prompts can display all kinds of information, but they are not part of the commands you are giving to your system. To disconnect from the system in graphical mode, you need to close all terminal windows and other applications. After that, hit the *logout* icon or find *Log Out* in the menu. Closing everything is not really necessary, and the system can do this for you, but session management might put all currently open applications back on your screen when you connect again, which takes longer and is not always the desired effect. However, this behavior is configurable.
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When you see the login screen again, asking to enter user name and password, logout was successful.
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Text Mode
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~~~~~~~~~
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One is in text mode when the whole screen is black, showing (in most cases white) characters. A text mode login screen typically shows some information about the machine you are working on, the name of the machine and a prompt waiting for you to log in.
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The login is different from a graphical login, in that you have to hit the *Enter* key after providing your user name, because there are no buttons on the screen that you can click with the mouse. Then you should type your password, followed by another *Enter*. You will not see any indication that you are entering something, not even an asterisk, and you won't see the cursor move. But this is normal on Linux and is done for security
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reasons.
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When the system has accepted you as a valid user, you may get some more information, called the *message of the day*, which can be anything. Additionally, it is popular on UNIX systems to display a fortune cookie, which contains some general wise or unwise (this is up to you) thoughts. After that, you will be given a shell, indicated with the same prompt that you would get in graphical mode.
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Also in text mode: log in as root only to do setup and configuration that absolutely requires administrator privileges, such as adding users, installing software packages, and performing network and other system configuration. Once you are finished, immediately leave the special account and resume your work as a non−privileged user.
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Logging out is done by entering the *logout* command, followed by Enter. You are successfully disconnected from the system when you see the login screen again.Don't power−off the computer after logging out. It is not meant to be shut off without application of the proper procedures for halting the system. Powering it off without going through the halting process might cause severe damage!
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Basic Commands
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===============
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ls
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---
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When invoked without any arguments, *ls* lists the files in the current working directory. A directory that is not the current working directory can be specified and ls will list the files there. The user also may specify any list of files and directories. In this case, all files and all contents of specified directories will be listed. The name *ls* is derived from *list segments* which was used in earlier systems.
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Files whose names start with "." are not listed, unless the *-a* flag is specified or the files are specified explicitly.
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Without options, *ls* displays files in a bare format. This bare format however makes it difficult to establish the type, permissions, and size of the files. The most common options to reveal this information or change the list of files are:
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    * *-l* long format, displaying Unix file types, permissions, number of hard links, owner, group, size, date, and filename
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    * *-F* appends a character revealing the nature of a file, for example, * for an executable, or / for a directory. Regular files have no suffix.
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    * *-a* lists all files in the given directory, including those whose names start with "." (which are hidden files in Unix). By default, these files are excluded from the list.
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    * *-R* recursively lists subdirectories. The command ls -R / would therefore list all files.
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    * *-d* shows information about a symbolic link or directory, rather than about the link's target or listing the contents of a directory.
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    * *-t* sort the list of files by modification time.
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    * *-h* print sizes in human readable format. (e.g., 1K, 234M, 2G, etc.)
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In some environments, providing the option *--color* (for GNU ls) or *-G* (FreeBSD ls) causes ls to highlight different types of files with different colors, instead of with characters as *-F* would. To determine what color to use for a file, GNU *ls* checks the Unix file type, the file permissions, and the file extension, while FreeBSD *ls* checks only the Unix file type and file permissions.::
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	$ ls
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	jeeves.rst psmith.html blandings.html
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	$ ls -l
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	drwxr--r--   1 plum  editors   4096  jeeves
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	-rw-r--r--   1 plum  editors  30405  psmith
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	-r-xr-xr-x   1 plum  plum      8460  blandings
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Here "$" actually is the beginning of the prompt. This is typical in most Unix-based systems.
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date
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-----
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The Unix date command displays the time and date. The super-user can use it to set the system clock.
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With no options, the date command displays the current date and time, including the abbreviated day name, abbreviated month name, day of the month, the time separated by colons, the timezone name, and the year. For example::
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	$date
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	Tue Sep  8 12:01:45 IST 2009
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On some systems to set the current date and time to September 8, 2004 01:22 you type::
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	$date --set="20040908 01:22"
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In order to view the various options for the *date* command, type::
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	$man date
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This will take you to the "Manual" page comprising of all the details on the *date* command. You can return to the terminal from the "man" page by pressing the *Esc* key in the keyboard and typing ":q" in that order. 
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cd
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---
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This stands for "change directory". When one wants to go up to the parent directory, bypassing the tree of directories one has entered, “ cd ..” can be used.
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One dot '.' represents the current directory while two dots '..' represent the parent directory.
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“ cd -” will return you to the previous directory (a bit like an “undo”).
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You can also use cd absolute path or cd relative path (see below):
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Absolute paths:
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    An “ absolute path” is easily recognised from the leading forward slash, /. The / means that you start at the top level directory and continue down.
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For example to get to /boot/grub you would type::
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	$cd /boot/grub
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This is an absolute path because you start at the top of the hierarchy and go downwards from there (it doesn't matter where in the filesystem you were when you typed the command).
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Relative paths:
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    A “ relative path” doesn't have a preceding slash. Use a relative path when you start from a directory below the top level directory structure. This is dependent on where you are in the filesystem.
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    For example if you are in root's home directory and want to get to /root/music, you type::
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	$ cd music
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Please note that there is no / using the above cd command. Using a / would cause this to be an absolute path, working from the top of the hierarchy downward.
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who
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----
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The standard Unix command *who* displays a list of users who are currently logged into a computer.
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The *who* command is related to the command *w*, which provides the same information but also displays additional data and statistics.::
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	$who
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	beeblebrox tty7         2009-09-08 10:50 (:0)
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	beeblebrox pts/0        2009-09-08 11:25 (:0.0)
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	dumbledore pts/1        2009-09-08 18:11 (potter.xyz.in)
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	beeblebrox pts/2        2009-09-08 18:53 (:0.0)
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The command can be invoked with the arguments *am i* or *am I* (so it is invoked as *who am i* or * who am I*), showing information about the current terminal only (see the *-m* option below, of which this invocation is equivalent).
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In order to find out the various options that can be appended to the *who* command, check the *man* page by typing out the following in the terminal::
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	$man who
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This will take you to the "Manual" page containing details about the *who* command
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mkdir
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-----
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This command is used to make a new directory. Normal usage is as straightforward as follows::
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	$mkdir name_of_directory
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Where *name_of_directory* is the name of the directory one wants to create. When typed as above (ie. normal usage), the new directory would be created within the current directory. On Unix, multiple directories can be specified, and *mkdir* will try to create all of them.
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Options
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~~~~~~~
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On Unix-like operating systems, *mkdir* takes options. Three of the most common options are:
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    * *-p*: will also create all directories leading up to the given directory that do not exist already. If the given directory already exists, ignore the error.
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    * *-v*: display each directory that mkdir creates. Most often used with -p.
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    * *-m*: specify the octal permissions of directories created by mkdir.
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*-p* is most often used when using mkdir to build up complex directory hierarchies, in case a necessary directory is missing or already there. -m is commonly used to lock down temporary directories used by shell scripts.
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Examples
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~~~~~~~~
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An example of *-p* in action is::
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	$mkdir -p /tmp/a/b/c
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If */tmp/a* exists but */tmp/a/b* does not, mkdir will create */tmp/a/b* before creating */tmp/a/b/c*.
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And an even more powerful command, creating a full tree at once (this however is a Shell extension, nothing mkdir does itself)::
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	$mkdir -p tmpdir/{trunk/sources/{includes,docs},branches,tags}
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This will create:
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tmpdir 	- branches
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	- tag
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	- trunk	- sources - includes
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			  - docs
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Getting Help
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============
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apropos and whatis
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-------------------
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This is a command to search the manual pages files in Unix and Unix-like operating systems. ::
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	$ apropos grep
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	egrep       egrep (1)       Search a file for a pattern using full regular expressions
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	fgrep       fgrep (1)       Search a file for a fixed-character	string
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	fmlgrep     fmlgrep (1)     Search a file for a pattern
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	grep        grep (1)        Search a file for a pattern
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	gzgrep      gzgrep (1)      Search a possibly compressed file for a regular expression
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	nisgrep     nismatch (1)    Utilities for searching NIS+ tables
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	pgrep       pgrep (1)       Find or signal a process by name or other attribute
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	zgrep       zgrep (1)       Search a possibly compressed file for a regular expression
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	...
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In this example, the user uses *apropos* to search for the string "grep", and apropos returns the indicated *man* pages that include the term "grep".
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A short index of explanations for commands is available using the *whatis* command, like in the examples below::
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	$whatis ls
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	ls (1) 		 - list directory contents
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This displays short information about a command, and the first section in the collection of man pages that contains an appropriate page.
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If you don't know where to get started and which man page to read, *apropos* gives more information. Say that you do not know how to start a browser, then you could enter the following command::
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	$apropos browser
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	gmusicbrowser (1)    - Jukebox for large collections of audio files
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	infobrowser (1)      - read Info documents
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	libsmbclient (7)     - An extension library for browsers and that 		can be used...
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	opera (1)            - a standards-compliant graphical Web browser
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	sensible-browser (1) - sensible editing, paging, and web browsing
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	smbtree (1)          - A text based smb network browser
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	tvtk_doc (1)         - A GUI based TVTK documentation search browser.
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	viewres (1)          - graphical class browser for Xt
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	w3m (1)              - a text based Web browser and pager
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	www-browser (1)      - a text based Web browser and pager
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	...
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man
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----
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Man pages (short for "manual pages") are the extensive documentation that comes preinstalled with almost all substantial Unix and Unix-like operating systems. The Unix command used to display them is *man*. Each page is a self-contained document.
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To read a manual page for a Unix command, one can use::
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	$ man <command_name>
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at a shell prompt; for example, "man ftp". In order to simplify navigation through the output, *man* generally uses the less terminal pager.
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Pages are traditionally referred to using the notation "name(section)"; for example, ftp(1). The same page name may appear in more than one section of the manual, this can occur when the names of system calls, user commands, or macro packages coincide. Two examples are *man(1)* and *man(7)*, or *exit(2)* and *exit(3)*. The syntax for accessing the non-default manual section varies between different man implementations. On Linux and *BSD, for example, the syntax for reading *printf(3)* is::
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	$man 3 printf
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Another example::
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	$man man
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The previous example will take you to the "Manual" page entry about manual pages!
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Layout
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~~~~~~
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All man pages follow a common layout that is optimized for presentation on a simple ASCII text display, possibly without any form of highlighting or font control. Sections present may include:
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NAME
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    The name of the command or function, followed by a one-line description of what it does.
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SYNOPSIS
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    In the case of a command, you get a formal description of how to run it and what command line options it takes. For program functions, a list of the parameters the function takes and which header file contains its definition. For experienced users, this may be all the documentation they need.
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DESCRIPTION
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    A textual description of the functioning of the command or function.
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EXAMPLES
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    Some examples of common usage.
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SEE ALSO
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    A list of related commands or functions.
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Other sections may be present, but these are not well standardized across man pages. Common examples include: OPTIONS, EXIT STATUS, ENVIRONMENT, KNOWN BUGS, FILES, AUTHOR, REPORTING BUGS, HISTORY and COPYRIGHT.
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These days virtually every Unix command line application comes with its man page, and many Unix users perceive a lack of man pages as a sign of low quality; indeed, some projects, such as Debian, go out of their way to write man pages for programs lacking one. Few alternatives to *man* have enjoyed much popularity, with the possible exception of the GNU project's "info" system, an early and simple hypertext system.
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However, the format of a single page for each application, the lack of classification within the sections and the relatively unsophisticated formatting facilities have motivated the development of alternative documentation systems, such as the previously mentioned "info" system.
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Most Unix GUI applications (particularly those built using the GNOME and KDE development environments) now provide end-user documentation in HTML and include embedded HTML viewers such as yelp for reading the help within the application.
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Usually the man pages are written in English. Translations into other languages can be also available on the system.
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The default format of the man pages is troff, with either the macro package man (appearance oriented) or on some systems mdoc (semantic oriented). This makes it possible to typeset a man page to PostScript, PDF and various other formats for viewing or printing.
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info
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-----
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*info* is a software utility which forms a hypertextual, multipage documentation and help viewer working on a command line interface, useful when there is no GUI available.
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The syntax is ::
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   380
	
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	$ info <command_name>
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*info* processes info files, which are Texinfo formatted files, and presents the documentation as a tree, with simple commands to traverse the tree and to follow cross references. For instance
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    - *n* goes to the next page.
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    - *p* goes to the previous page.
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    - *u* goes to the upper page.
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    - *l* goes to the last(visited) node
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    - To follow a cross reference, the cursor can be moved over a link (a word preceded by a `*`) and enter pressed.
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   390
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   391
info was initially written for use with GNU/Linux and then ported to other Unix-like operating systems.
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--help
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   394
-------
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   395
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   396
Most GNU commands support the --help, which gives a short explanation about how to use the command and a list of available options. Below is the output of this option with the *cat* command::
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   397
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	$ userprompt@host: cat --help
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	Usage: cat [OPTION] [FILE]...
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	Concatenate FILE(s), or standard input, to standard output.
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   401
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	  -A, --show-all           equivalent to -vET
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	  -b, --number-nonblank    number nonempty output lines
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	  -e                       equivalent to -vE
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	  -E, --show-ends          display $ at end of each line
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	  -n, --number             number all output lines
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	  -s, --squeeze-blank      suppress repeated empty output lines
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	  -t                       equivalent to -vT
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   409
	  -T, --show-tabs          display TAB characters as ^I
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   410
	  -u                       (ignored)
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	  -v, --show-nonprinting   use ^ and M- notation, except for LFD and 		  TAB
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	  --help     display this help and exit
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      	  --version  output version information and exit
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   414
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	With no FILE, or when FILE is -, read standard input.
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   416
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   417
	Examples:
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	  cat f - g  Output f's contents, then standard input, then g's 	  contents.
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	  cat        Copy standard input to standard output.
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   420
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	Report bugs to <bug-coreutils@gnu.org>.
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   424
Basic file handling
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===================
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cp
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---
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   429
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*cp* is the command entered in a Unix shell to copy a file from one place to another, possibly on a different filesystem. The original file remains unchanged, and the new file may have the same or a different name.
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   431
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   432
Usage
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   433
~~~~~
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   434
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   435
To copy a file to another file::
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   436
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   437
	$ cp [ -f ] [ -H ] [ -i ] [ -p ][ -- ] SourceFile TargetFile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   438
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   439
To copy a file to a directory::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   440
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   441
	$ cp [ -f ] [ -H ] [ -i ] [ -p ] [ -r | -R ] [ -- ] SourceFile ... 		TargetDirectory
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   442
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   443
To copy a directory to a directory::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   444
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   445
	$ cp [ -f ] [ -H ] [ -i ] [ -p ] [ -- ] { -r | -R } 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   446
	SourceDirectory ... TargetDirectory
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   447
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   448
Flags
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   449
~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   450
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   451
*-f* (force) – specifies removal of the target file if it cannot be opened for write operations. The removal precedes any copying performed by the cp command.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   452
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   453
*-P* – makes the cp command copy symbolic links. The default is to follow symbolic links, that is, to copy files to which symbolic links point.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   454
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   455
*-i* (interactive) – prompts you with the name of a file to be overwritten. This occurs if the TargetDirectory or TargetFile parameter contains a file with the same name as a file specified in the SourceFile or SourceDirectory parameter. If you enter y or the locale's equivalent of y, the cp command continues. Any other answer prevents the cp command from overwriting the file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   456
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   457
*-p* (preserve) – duplicates the following characteristics of each SourceFile/SourceDirectory in the corresponding TargetFile and/or TargetDirectory:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   458
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   459
    * The time of the last data modification and the time of the last access.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   460
    * The user ID and group ID (only if it has permissions to do this)
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   461
    * The file permission bits and the SUID and SGID bits.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   462
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   463
*-R* (recursive) – copy directories (recursively copying all the contents)
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   464
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   465
Examples
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   466
~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   467
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   468
To make a copy of a file in the current directory, enter::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   469
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   470
    $ cp prog.c prog.bak
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   471
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   472
This copies prog.c to prog.bak. If the prog.bak file does not already exist, the cp command creates it. If it does exist, the cp command replaces it with a copy of the prog.c file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   473
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   474
To copy a file in your current directory into another directory, enter::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   475
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   476
    $ cp zaphod /home/books/hhgg
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   477
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   478
This copies the jones file to /home/books/hhgg/zaphod.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   479
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   480
To copy a file to a new file and preserve the modification date, time, and access control list associated with the source file, enter::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   481
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   482
    $ cp -p martin_luther_king martin_luther_king.jr
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   483
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   484
This copies the *martin_luther_king* file to the *martin_luther_king.jr* file. Instead of creating the file with the current date and time stamp, the system gives the *martin_luther_king.jr* file the same date and time as the *martin_luther_king* file. The *martin_luther_king.jr* file also inherits the *martin_luther_king* file's access control protection.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   485
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   486
To copy all the files in a directory to a new directory, enter::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   487
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   488
    $ cp /home/galactica/clients/* /home/hhgg/customers
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   489
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   490
This copies only the files in the clients directory to the customers directory.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   491
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   492
To copy a directory, including all its files and subdirectories, to another directory, enter:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   493
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   494
    $ cp -R /home/hhgg/clients /home/hhgg/customers
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   495
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   496
This copies the clients directory, including all its files, subdirectories, and the files in those subdirectories, to the customers/clients directory.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   497
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   498
To copy a specific set of files of any extension to another directory, enter::
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   499
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   500
    $ cp zaphod arthur ford /home/hhgg/clients
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   501
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   502
This copies the *zaphod*, *arthur*, and *ford* files in your current working directory to the /home/hhgg/clients directory.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   503
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   504
To use pattern-matching characters to copy files, enter::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   505
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   506
    $ cp programs/*.py .
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   507
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   508
This copies the files in the programs directory that end with *.py* to the current directory, signified by the single "." (dot). You must type a space between the *py* and the final dot.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   509
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   510
mv
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   511
---
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   512
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   513
*mv* (short for move) is a Unix command that moves one or more files or directories from one place to another. The original file is deleted, and the new file may have the same or a different name. If possible (i.e. when the original and new files are on the same file system), *mv* will rename the file instead. Write permission is required on all directories being modified.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   514
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   515
Conflicting existing file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   516
~~~~~~~~~~~~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   517
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   518
In all cases, when a file is moved to have the name of an existing file (in the same directory), the existing file is deleted. If the existing file is not writable but is in a directory that is writable, then the mv command asks for confirmation if possible (i.e. if run from a terminal) before proceeding, unless the -f (force) option is used.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   519
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   520
Differences with copy and delete
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   521
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   522
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   523
Note that, usually, when moving files within the same volume, moving (and/or renaming) is not the same as simply copying and then deleting the original. When moving a file, the link is simply removed from the old parent directory and added to the new parent directory. However, the file itself is untouched (i.e. it has the same inodes and resides at the same place on the disk). For example, you cannot copy a file you cannot read, but you can move (and/or rename) it (provided you have write permission to its old and new parent directories). Also, suppose there is a non-empty directory you do not have write permission to. You cannot delete this directory (since you cannot delete its contents); but you can move (and/or rename) it. Also, since moving between filenames on a single volume does not involve copying, it is faster and does not place strain of lots of reads and writes on the disk. Moving files across different volumes, however, does necessitate copying and deleting.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   524
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   525
Examples
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   526
~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   527
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   528
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   529
	$ mv myfile mynewfilename    renames a file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   530
	$ mv myfile otherfilename    renames a file and deletes the existing 		file "myfile"
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   531
	$ mv myfile /myfile          moves 'myfile' from the current 		directory to the root directory
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   532
	$ mv myfile dir/myfile       moves 'myfile' to 'dir/myfile' relative 		to the current directory
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   533
	$ mv myfile dir              same as the previous command (the 		filename is implied to be the same)
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   534
	$ mv myfile dir/myfile2      moves 'myfile' to dir and renames it to 		'myfile2'
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   535
	$ mv foo bar baz dir         moves multiple files to directory dir
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   536
	$ mv --help                  shows a very concise help about the 		syntax of the command
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   537
	$ man mv                     prints an extensive user manual for 		'mv' in the terminal
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   538
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   539
In all cases, the file or files being moved or renamed can be a directory.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   540
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   541
Note that when the command is called with two arguments (as *mv name1 name2* or *mv name1 /dir/name2*), it can have three different effects, depending on whether *name2* does not exist, is an existing file, or is an existing directory. If the user intends to refer to an existing directory, */.* (or in some Unix versions */* is sufficient) may be appended to the name to force the system to check this. To move a file to a new directory, the directory must be created first.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   542
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   543
rm
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   544
---
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   545
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   546
*rm* (short for "remove") is one of several basic Unix command lines that operates on files. It is used to delete files from a filesystem. The data is not actually destroyed. Only the index listing where the file is stored is destroyed, and the storage is made available for reuse. There are undelete utilities that will attempt to reconstruct the index and can bring the file back if the parts were not reused.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   547
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   548
Here's example to remove a file named "foo" from a directory, here shown with the -i option::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   549
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   550
  	$ rm -i foo
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   551
    	remove foo? y
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   552
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   553
Options
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   554
~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   555
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   556
Common options that rm accepts include:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   557
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   558
    * *-r*, which removes directories, removing the contents recursively beforehand (so as not to leave files without a directory to reside in) ("recursive")
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   559
    * *-i*, which asks for every deletion to be confirmed ("interactive")
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   560
    * *-f*, which ignores non-existent files and overrides any confirmation prompts ("force")
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   561
    * *-v*, which shows what is being removed as it happens ("verbose")
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   562
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   563
*rm* is often aliased to "rm -i" so as to avoid accidental deletion of files. If a user still wishes to delete a large number of files without confirmation, they can manually cancel out the -i argument by adding the -f option (as the option specified later on the expanded command line "rm -i -f" takes precedence).
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   564
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   565
*rm -rf* (variously, rm -rf /, rm -rf `*`, and others) is frequently used in jokes and anecdotes about Unix disasters. The rm -rf variant of the command, if run by a superuser on the root directory, would cause the contents of every writable mounted filesystem on the computer to be deleted.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   566
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   567
*rm* is often used in conjunction with xargs to supply a list of files to delete::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   568
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   569
	xargs rm < filelist
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   570
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   571
When *rm* is used on a symbolic link, it deletes the link, but does not affect the target of the link.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   572
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   573
Permissions
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   574
~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   575
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   576
Usually, on most filesystems, deleting a file requires write permission on the parent directory (and execute permission, in order to enter the directory in the first place). (Note that, confusingly for beginners, permissions on the file itself are irrelevant. However, GNU rm asks for confirmation if a write-protected file is to be deleted, unless the -f option is used.)
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   577
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   578
To delete a directory (with rm -r), one must delete all of its contents recursively. This requires that one must have read and write and execute permission to that directory (if it's not empty) and all non-empty subdirectories recursively (if there are any). The read permissions are needed to list the contents of the directory in order to delete them. This sometimes leads to an odd situation where a non-empty directory cannot be deleted because one doesn't have write permission to it and so cannot delete its contents; but if the same directory were empty, one would be able to delete it.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   579
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   580
If a file resides in a directory with the sticky bit set, then deleting the file requires one to be the owner of the file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   581
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   582
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   583
Command Line Arguments
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   584
=======================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   585
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   586
In computer command line interfaces, a command line argument is an argument sent to a program being called. In general, a program can take any number of command line arguments, which may be necessary for the program to run, or may even be ignored, depending on the function of that program.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   587
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   588
For example, in Unix and Unix-like environments, an example of a command-line argument is::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   589
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   590
	rm file.s
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   591
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   592
"file.s" is a command line argument which tells the program rm to remove the file "file.s".
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   593
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   594
Programming languages such as C, C++ and Java allow a program to interpret the command line arguments by handling them as string parameters in the main function.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   595
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   596
A command line option or simply *option* (also known as a command line parameter, flag, or a switch) is an indication by a user that a computer program should change its default output.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   597
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   598
Long options are introduced via "--", and are typically whole words. For example, *ls --long --classify --all*. Arguments to long options are provided with "=", as *ls --block-size=1024*. Some Unix programs use long options with single dashes, for example MPlayer as in *mplayer -nosound*.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   599
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   600
Linux also uses "--" to terminate option lists. For example, an attempt to delete a file called *-file1* by using *rm -file1* may produce an error, since rm may interpret *-file1* as a command line switch. Using *rm -- -file1* removes ambiguity.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   601
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   602
Basic Text Processing
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   603
======================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   604
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   605
head
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   606
-----
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   607
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   608
*head* is a program on Unix and Unix-like systems used to display the first few lines of a text file or piped data. The command syntax is::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   609
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   610
	$ head [options] <file_name>
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   611
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   612
By default, *head* will print the first 10 lines of its input to the standard output. The number of lines printed may be changed with a command line option. The following example shows the first 20 lines of filename::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   613
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   614
	$ head -n 20 filename
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   615
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   616
This displays the first 5 lines of all files starting with *foo*::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   617
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   618
	$ head -n 5 foo*
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   619
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   620
Some versions omit the n and just let you say -5.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   621
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   622
Flags
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   623
~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   624
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   625
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   626
	-c <x number of bytes> Copy first x number of bytes.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   627
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   628
Other options: *sed*
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   629
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   630
Many early versions of Unix did not have this command, and so documentation and books had *sed* do this job::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   631
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   632
	sed 5q foo
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   633
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   634
This says to print every line (implicit), and quit after the fifth.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   635
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   636
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   637
tail
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   638
----
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   639
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   640
*tail* is a program on Unix and Unix-like systems used to display the last few lines of a text file or piped data.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   641
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   642
The command-syntax is::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   643
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   644
	$ tail [options] <file_name>
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   645
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   646
By default, *tail* will print the last 10 lines of its input to the standard output. With command line options the number of lines printed and the printing units (lines, blocks or bytes) may be changed. The following example shows the last 20 lines of filename::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   647
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   648
	$ tail -n 20 filename
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   649
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   650
This example shows the last 15 bytes of all files starting with *foo*::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   651
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   652
	$ tail -c 15 foo*
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   653
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   654
This example shows all lines of filename from the second line onwards::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   655
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   656
	$ tail -n +2 filename
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   657
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   658
Using an older syntax (still used in Sun Solaris as the -n option is not supported), the last 20 lines and the last 50 bytes of filename can be shown with the following command::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   659
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   660
	$ tail -20 filename
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   661
	$ tail -50c filename
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   662
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   663
However this syntax is now obsolete and does not conform with the POSIX 1003.1-2001 standard. Even if still supported in current versions, when used with other options (like -f, see below), these switches could not work at all.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   664
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   665
File monitoring
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   666
~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   667
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   668
*tail* has a special command line option *-f* (follow) that allows a file to be monitored. Instead of displaying the last few lines and exiting, tail displays the lines and then monitors the file. As new lines are added to the file by another process, tail updates the display. This is particularly useful for monitoring log files. The following command will display the last 10 lines of messages and append new lines to the display as new lines are added to messages::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   669
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   670
	$ tail -f /var/adm/messages
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   671
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   672
To interrupt tail while it is monitoring, break-in with *Ctrl+C*. This command can be run "in the background" with &, see job control.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   673
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   674
If you have a command's result to monitor, you can use the *watch* command.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   675
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   676
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   677
cut
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   678
----
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   679
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   680
In computing, *cut* is a Unix command line utility which is used to extract sections from each line of input — usually from a file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   681
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   682
Extraction of line segments can typically be done by *bytes (-b), characters (-c)*, or *fields (-f)* separated by a *delimiter (-d — the tab character by default)*. A range must be provided in each case which consists of one of N, N-M, N- (N to the end of the line), or -M (beginning of the line to M), where N and M are counted from 1 (there is no zeroth value). Since version 6, an error is thrown if you include a zeroth value. Prior to this the value was ignored and assumed to be 1.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   683
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   684
Assuming a file named file containing the lines::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   685
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   686
	foo:bar:baz:qux:quux
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   687
	one:two:three:four:five:six:seven
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   688
	alpha:beta:gamma:delta:epsilon:zeta:eta:teta:iota:kappa:lambda:mu
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   689
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   690
To output the fourth through tenth characters of each line::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   691
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   692
	$ cut -c 4-10 file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   693
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   694
This gives the output::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   695
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   696
	:bar:ba
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   697
	:two:th
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   698
	ha:beta
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   699
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   700
To output the fifth field through the end of the line of each line using the colon character as the field delimiter::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   701
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   702
	$ cut -d : -f 5- file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   703
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   704
This gives the output::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   705
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   706
	quux
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   707
	five:six:seven
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   708
	epsilon:zeta:eta:teta:iota:kappa:lambda:mu
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   709
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   710
paste
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   711
------
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   712
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   713
*paste* is a Unix command line utility which is used to join files horizontally (parallel merging) by outputting lines consisting of the sequentially corresponding lines of each file specified, separated by tabs, to the standard output. It is effectively the horizontal equivalent to the utility *cat* command which operates on the vertical plane of two or more files.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   714
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   715
To paste several columns of data together into the file *www* from files *who*, *where*, and *when*::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   716
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   717
	$ paste who where when > www
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   718
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   719
If the files contain:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   720
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   721
+-----------+------------+------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   722
|   who     |   where    |    when    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   723
+===========+============+============+
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   724
|  Batman   | GothamCity | January 3  |
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   725
+-----------+------------+------------+	
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   726
| Trillian  | Andromeda  | February 4 |
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   727
+-----------+------------+------------+
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   728
|  Jeeves   | London     |  March 19  |
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   729
+-----------+------------+------------+	
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   730
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   731
This creates the file named *www* containing::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   732
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   733
	Batman            GothamCity       January 3
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   734
	Trillian          Andromeda        February 4
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   735
	Jeeves            London           March 19
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   736
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   737
Shell Meta Characters
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   738
======================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   739
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   740
Unix recognizes certain special characters, called "meta characters," as command directives. The shell meta characters are recognized anywhere they appear in the command line, even if they are not surrounded by blank space. For that reason, it is safest to only use the characters A-Z, a-z, 0-9, and the period, dash, and underscore characters when naming files and directories on Unix. If your file or directory has a shell meta character in the name, you will find it difficult to use the name in a shell command.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   741
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   742
The shell meta characters include:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   743
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   744
\ / < > ! $ % ^ & * | { } [ ] " ' ` ~ ; 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   745
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   746
Different shells may differ in the meta characters recognized.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   747
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   748
As an example,
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   749
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   750
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   751
	$ ls file.*
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   752
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   753
run on a directory containing the files file, file.c, file.lst, and myfile would list the files file.c and file.lst. However,::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   754
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   755
	$ ls file.?
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   756
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   757
run on the same directory would only list file.c because the ? only matches one character, no more, no less. This can save you a great deal of typing time. For example, if there is a file called california_cornish_hens_with_wild_rice and no other files whose names begin with 'c', you could view the file without typing the whole name by typing this::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   758
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   759
	$ more c*
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   760
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   761
because the c* matches that long file name.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   762
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   763
Filenames containing metacharacters can pose many problems and should never be intentionally created. If you do find that you've created a file with metacharacters, and you would like to remove it, you have three options. You may use wildcards to match metacharacter, use the \  to directly enter the filename, or put the command in double quotes (except in the case of double quotes within the file name, these must be captured with one of the first two methods). For example, deleting a file named `"``*`|more`"` can be accomplished with::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   764
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   765
	$ rm ??more
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   766
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   767
or::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   768
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   769
	$ rm $\backslash$*$\backslash$|more
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   770
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   771
or::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   772
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   773
	$ rm ''*|more'' 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   774
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   775
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   776
Looking At Files
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   777
================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   778
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   779
cat
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   780
---
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   781
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   782
The *cat* command is a standard Unix program used to concatenate and display files. The name is from "catenate", a synonym of *concatenate*.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   783
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   784
The Single Unix Specification specifies the behavior that the contents of each of the files given in sequence as arguments will be written to the standard output in the same sequence, and mandates one option, -u, where each byte is printed as it is read.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   785
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   786
If the filename is specified as -, then *cat* will read from standard input at that point in the sequence. If no files are specified, *cat* will read from standard input entered.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   787
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   788
Jargon File Definition
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   789
~~~~~~~~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   790
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   791
The Jargon File version 4.4.7 lists this as the definition of *cat*::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   792
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   793
   1. To spew an entire file to the screen or some other output sink without
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   794
 	pause (syn. blast).
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   795
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   796
   2. By extension, to dump large amounts of data at an unprepared target or
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   797
 	with no intention of browsing it carefully. Usage: considered silly.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   798
 	Rare outside Unix sites. See also dd, BLT.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   799
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   800
	Among Unix fans, *cat(1)* is considered an excellent example of
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   801
 	user-interface design, because it delivers the file contents without 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   802
	such verbosity as spacing or headers between the files, and because 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   803
	it does not require the files to consist of lines of text, but works 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   804
	with any sort of data.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   805
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   806
	Among Unix critics, *cat(1)* is considered the canonical example of 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   807
	bad user-interface design, because of its woefully unobvious name. 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   808
	It is far more often used to blast a single file to standard output 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   809
	than to concatenate two or more files. The name cat for the former 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   810
	operation is just as unintuitive as, say, LISP's cdr.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   811
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   812
	Of such oppositions are holy wars made...
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   813
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   814
Useless Use of 'cat'
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   815
~~~~~~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   816
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   817
UUOC (from comp.unix.shell on Usenet) stands for “Useless Use of cat”. As it is observed on *comp.unix.shell*, “The purpose of cat is to concatenate (or 'catenate') files. If it's only one file, concatenating it with nothing at all is a waste of time, and costs you a process.”
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   818
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   819
Nevertheless one sees people doing::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   820
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   821
	$ cat file | some_command and its args ...
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   822
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   823
instead of the equivalent and cheaper::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   824
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   825
	<file some_command and its args ...
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   826
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   827
or (equivalently and more classically)::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   828
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   829
	some_command and its args ... <file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   830
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   831
Since 1995, occasional awards for UUOC have been given out. The activity of fixing instances of UUOC is sometimes called 'demoggification'.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   832
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   833
Amongst many, it is still considered safer to use *cat* for such cases given that the < and > keys are next to each other in many popular keyboard mappings. While the risk might be low, the impact of using > instead of < can be high and prohibitive.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   834
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   835
zcat
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   836
~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   837
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   838
*zcat* is a Unix program similar to *cat*, that decompresses individual files and concatenates them to standard output. Traditionally *zcat* operated on files compressed by compress but today it is usually able to operate on *gzip* or even *bzip2* archives. On such systems, it is equivalent to *gunzip -c*
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   839
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   840
more
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   841
-----
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   842
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   843
In computing, *more* is a command to view (but not modify) the contents of a text file one screen at a time (terminal pager). It is available on Unix and Unix-like systems, DOS, OS/2 and Microsoft Windows. Programs of this sort are called pagers.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   844
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   845
Usage
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   846
~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   847
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   848
The command-syntax is::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   849
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   850
	$ more [options] [file_name]
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   851
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   852
If no file name is provided, *more* looks for input from stdin.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   853
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   854
Once *more* has obtained input, it displays as much as can fit on the current screen and waits for user input to advance, with the exception that a form feed (^L) will also cause *more* to wait at that line, regardless of the amount of text on the screen. In the lower-left corner of the screen is displayed the text "--More--" and a percentage, representing the percent of the file that *more* has paged through. (This percentage includes the text displayed on the current screen.) When *more* reaches the end of a file (100%) it exits. The most common methods of navigating through a file are *Enter*, which advances the output by one line, and *Space*, which advances the output by one screen.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   855
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   856
There are also other commands that can be used while navigating through the document; consult *more*'s *man* page for more details.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   857
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   858
*Options* are typically entered before the file name, but can also be entered in the environment variable *$MORE*. Options entered in the actual command line will override those entered in the *$MORE* environment variable. Available options may vary between Unix systems.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   859
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   860
less
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   861
-----
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   862
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   863
*less* is a terminal pager program on Unix, Windows and Unix-like systems used to view (but not change) the contents of a text file one screen at a time. It is similar to *more*, but has the extended capability of allowing both forward and backward navigation through the file. Unlike most Unix text editors/viewers, *less* does not need to read the entire file before starting, resulting in faster load times with large files.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   864
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   865
Usage
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   866
~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   867
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   868
*less* can be invoked with options to change its behaviour, for example, the number of lines to display on the screen. A few options vary depending on the operating system. While *less* is displaying the file, various commands can be used to navigate through the file. These commands are based on those used by both *more* and *vi*. It is also possible to search for character patterns in the file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   869
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   870
By default, *less* displays the contents of the file to the standard output (one screen at a time). If the file name argument is omitted, it displays the contents from standard input (usually the output of another command through a pipe). If the output is redirected to anything other than a terminal, for example a pipe to another command, less behaves like cat.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   871
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   872
The command-syntax is::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   873
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   874
	$ less [options] file_name
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   875
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   876
Frequently Used Options
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   877
~~~~~~~~~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   878
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   879
    * -g: Highlights just the current match of any searched string.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   880
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   881
    * -I: Case-insensitive searches.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   882
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   883
    * -M: Shows more detailed prompt, including file position.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   884
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   885
    * -N: Shows line numbers (useful for source code viewing).
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   886
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
   887
    * -S: Disables line wrap ("chop long lines"). Long lines can be seen by side scrolling.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   888
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   889
    * -?: Shows help.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   890
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   891
Frequently Used Commands
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   892
~~~~~~~~~~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   893
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   894
    * [Arrows]/[Page Up]/[Page Down]/[Home]/[End]: Navigation.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   895
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   896
    * [Space bar]: Next page.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   897
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   898
    * b: Previous page.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   899
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   900
    * ng: Jump to line number n. Default is the start of the file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   901
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   902
    * nG: Jump to line number n. Default is the end of the file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   903
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   904
    * /pattern: Search for pattern. Regular expressions can be used.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   905
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   906
    * '^ or g: Go to start of file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   907
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   908
    * '$ or G: Go to end of file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   909
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   910
    * s: Save current content (got from another program like grep) in a file.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   911
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   912
    * =: File information.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   913
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   914
    * h: Help.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   915
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   916
    * q: Quit.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   917
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   918
Examples 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   919
~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   920
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   921
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   922
	$ less -M readme.txt                     #Read "readme.txt."
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   923
	$ less +F /var/log/mail.log              #Follow mode for log
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   924
	$ file * | less                          #Easier file analysis.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   925
	$ grep -i void *.c | less -I -p void     #Case insensitive search 		                                          for "void" in all .c files
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   926
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   927
Directory Structure
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   928
====================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   929
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   930
In the File Hierarchy Standard (FHS) all files and directories appear under the root directory "/", even if they are stored on different physical devices. Note however that some of these directories may or may not be present on a Unix system depending on whether certain subsystems, such as the X Window System, are installed.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   931
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   932
The majority of these directories exist in all UNIX operating systems and are generally used in much the same way; however, the descriptions here are those used specifically for the FHS, and are not considered authoritative for platforms other than Linux.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   933
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   934
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   935
|   Directory   |             Description                        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   936
+===============+================================================+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   937
| /             | Primary hierarchy root and root directory of   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   938
|               | the entire file system hierarchy.              |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   939
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   940
| /bin/         | Essential command binaries that need to be     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   941
|               | available in single user mode; for all users,  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   942
|               | e.g., *cat*, *ls*, *cp*.                       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   943
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   944
| /boot/        | Boot loader files, e.g., *kernels*, *initrd*;  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   945
|               | often a separate partition.                    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   946
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   947
| /dev/         | Essential devices, e.g., /dev/null             |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   948
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   949
| /etc/         | Host-specific system-wide configuration files  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   950
|               | (the name comes from *et cetera*)              |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   951
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   952
| /home/        | User's home directories, containing saved      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   953
|               | files, personal settings, etc.; often a        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   954
|               | separate partition.                            |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   955
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   956
| /lib/         | Libraries essential for the binaries in        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   957
|               | */bin/* and */sbin/*                           |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   958
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   959
| /media/       | Mount points for removable media such as       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   960
|               | CD-ROMs, external hard disks, USB sticks, etc. |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   961
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   962
| /mnt/         | Temporarily mounted file systems               |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   963
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   964
| /opt/         | Optional application software packages         |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   965
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   966
| /proc/        | Virtual filesystem documenting kernel and      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   967
|               | process status as text files; e.g., uptime,    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   968
|               | network. In Linux, corresponds to a *Procfs*   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   969
|               | mount.                                         |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   970
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   971
| /root/        | Home directory for the root user               |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   972
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   973
| /sbin/        | Essential system binaries; e.g., *init*,       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   974
|               | *route*, *mount*.                              |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   975
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   976
| /srv/         | Site-specific data which is served by the      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   977
|               | system.                                        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   978
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   979
| /tmp/         | Temporary files. Often not preserved between   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   980
|               | system reboots.                                |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   981
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   982
| /usr/         | Secondary hierarchy for read-only user data;   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   983
|               | contains the majority of (multi-)user          |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   984
|               | utilities and applications.                    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   985
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   986
| /var/         | Variable files - files whose content is        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   987
|               | expected to continually change during normal   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   988
|               | operation of the system - such as logs, spool  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   989
|               | files, and temporary e-mail files.             |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   990
|               | Sometimes a separate partition.                |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   991
+---------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   992
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   993
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   994
man hier
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
   995
---------
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   996
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   997
This is the manual page on the UNIX filesystem. The syntax for this is::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   998
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
   999
	$ man hier
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1000
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1001
ls -l
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1002
-----
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1003
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1004
Shows you huge amounts of information (permissions, owners, size, and when last modified) for folders and files. The syntax is ::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1005
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1006
	$ ls -l
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1007
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1008
This can be done after entering the required directory. 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1009
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1010
Permissions and Ownership
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1011
=========================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1012
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1013
chmod
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1014
------
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1015
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1016
The *chmod* command (abbreviated from 'change mode') is a shell command and C language function in Unix and Unix-like environments. When executed, it can change file system modes of files and directories. The modes include permissions and special modes.A chmod command first appeared in AT&T Unix version 1, and is still used today on Unix-like machines.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1017
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1018
Usage
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1019
~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1020
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1021
The *chmod* command options are specified like this:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1022
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1023
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1024
	$ chmod [options] mode[,mode] file1 [file2 ...]
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1025
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1026
To view what the permissions currently are, type:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1027
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1028
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1029
	$ ls -l file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1030
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1031
Command line options
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1032
~~~~~~~~~~~~~~~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1033
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1034
The *chmod* command has a number of command line options that affect its behavior. The most common options are:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1035
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1036
    * -R: Changes the modes of directories and files recursively
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1037
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1038
    * -v: Verbose mode; lists all files as they are being processed
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1039
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1040
Symbolic modes
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1041
+++++++++++++++
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1042
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1043
To the *chmod* utility, all permissions and special modes are represented by its mode parameter. One way to adjust the mode of files or directories is to specify a symbolic mode. The symbolic mode is composed of three components, which are combined to form a single string of text:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1044
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1045
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1046
	$ chmod [references][operator][modes] file1 ...
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1047
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1048
The references (or classes) are used to distinguish the users to whom the permissions apply. If no references are specified it defaults to “all” but modifies only the permissions allowed by the umask. The references are represented by one or more of the following letters:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1049
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1050
+--------------+--------+---------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1051
| Reference    | Class  |                Description                  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1052
+==============+========+=============================================+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1053
|      u       | user   | the owner of the file                       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1054
+--------------+--------+---------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1055
|      g       | group  | users who are members of the file's group   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1056
+--------------+--------+---------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1057
|      o       | others | users who are not hte owner of the file or  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1058
|              |        | members of the group                        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1059
+--------------+--------+---------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1060
|      a       | all    | all three of the above; is the same as *ugo*|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1061
+--------------+--------+---------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1062
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1063
The *chmod* program uses an operator to specify how the modes of a file should be adjusted. The following operators are accepted:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1064
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1065
+--------------+------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1066
| Operator     |                      Description                     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1067
+==============+======================================================+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1068
| +            | adds the specified modes to the specified classes    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1069
+--------------+------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1070
| -            | removes the specified modes from the specified       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1071
|              | classes                                              |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1072
+--------------+------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1073
| =            | the modes specified are to be made the exact modes   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1074
|              | for the specified classes                            |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1075
+--------------+------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1076
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1077
The modes indicate which permissions are to be granted or taken away from the specified classes. There are three basic modes which correspond to the basic permissions:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1078
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1079
+-----+--------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1080
|Mode |    Name      |                 Description                    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1081
+=====+==============+================================================+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1082
| r   | read         | read a file or list a directory's contents     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1083
+-----+--------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1084
| w   | write        | write to a file or directory                   |   
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1085
+-----+--------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1086
| x   | execute      | execute a file or recurse a directory tree     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1087
+-----+--------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1088
| X   | special      | which is not a permission in itself but rather |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1089
|     | execute      | can be used instead of 'x'. It applies execute |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1090
|     |              | permissions to directories regardless of their |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1091
|     |              | current permissions and applies execute        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1092
|     |              | permissions to a file which already has at     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1093
|     |              | least 1 execute permission bit already set     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1094
|     |              | (either user, group or other). It is only      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1095
|     |              | really useful when used with '+' and usually   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1096
|     |              | in combination with the *-R* option for giving |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1097
|     |              | group or other access to a big directory tree  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1098
|     |              | without setting execute permission on normal   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1099
|     |              | files (such as text files), which would        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1100
|     |              | normally happen if one just used 'chmod -R     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1101
|     |              | a+rx .', whereas with 'X' one can do 'chmod -R |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1102
|     |              | a+rX .' instead.                               |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1103
+-----+--------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1104
| s   | setuid/gid   | are Unix access rights flags that allow users  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1105
|     |              | to run an executable with the permissions of   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1106
|     |              | the executable's owner or group.They are often |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1107
|     |              | used to allow users on a computer system to run| 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1108
|     |              | programs with temporarily elevated privileges  | 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1109
|     |              | in order to perform a specific task. While the |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1110
|     |              | assumed user id or group id privileges provided|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1111
|     |              | are not always elevated, at a minimum they are | 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1112
|     |              | specific.They are needed for tasks that require|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1113
|     |              | higher privileges than those which a common    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1114
|     |              | user has, such as changing his or her login    |  
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1115
|     |              | password.                                      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1116
+-----+--------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1117
| t   | sticky       | The most common use of the sticky bit today is |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1118
|     |              | on directories, where, when set, items inside  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1119
|     |              | the directory can be renamed or deleted only by|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1120
|     |              | the item's owner, the directory's owner, or the| 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1121
|     |              | superuser; without the sticky bit set, any user|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1122
|     |              | with write and execute permissions for the     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1123
|     |              | directory can rename or delete contained files,| 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1124
|     |              | regardless of owner.                           |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1125
+-----+--------------+------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1126
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1127
The combination of these three components produces a string that is understood by the chmod command. Multiple changes can be specified by separating multiple symbolic modes with commas.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1128
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1129
Symbolic examples
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1130
+++++++++++++++++
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1131
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1132
Add the 'read' and 'write' permissions to the 'user' and 'group' classes of a directory:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1133
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1134
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1135
	$ chmod ug+rw mydir
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1136
	$ ls -ld mydir
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1137
	drw-rw----   2 starwars  yoda  96 Dec 8 12:53 mydir
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1138
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1139
For a file, remove *write* permissions for all classes:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1140
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1141
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1142
	$ chmod a-w myfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1143
	$ ls -l myfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1144
	-r-xr-xr-x   2 starwars  yoda 96 Dec 8 12:53 myfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1145
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1146
Set the permissions for the *u*ser and the *g*roup to read and execute only (no write permission) on *mydir*.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1147
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1148
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1149
	$ chmod ug=rx mydir
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1150
	$ ls -ld mydir
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1151
	dr-xr-x---   2 starwars  yoda 96 Dec 8 12:53 mydir
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1152
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1153
Octal numbers
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1154
+++++++++++++
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1155
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1156
The *chmod* command also accepts three and four-digit octal numbers representing modes. Using a three-digit octal number to set the modes of a file named myfile :
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1157
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1158
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1159
	$ chmod 664 myfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1160
	$ ls -l myfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1161
	-rw-rw-r--  1   57 Jul  3 10:13  myfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1162
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1163
Since the *setuid*, *setgid* and *sticky* bits are not set, this is equivalent to:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1164
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1165
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1166
	$ chmod 0664 myfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1167
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1168
Special modes
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1169
+++++++++++++
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1170
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1171
The *chmod* command is also capable of changing the additional permissions or special modes of a file or directory. The symbolic modes use **s** to represent the *setuid* and *setgid* modes, and **t** to represent the sticky mode. The modes are only applied to the appropriate classes, regardless of whether or not other classes are specified.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1172
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1173
Most operating systems support the specification of special modes using octal modes, but some do not. On these systems, only the symbolic modes can be used.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1174
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1175
Redirection and Piping
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1176
=======================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1177
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1178
In computing, *redirection* is a function common to most command-line interpreters, including the various Unix shells that can redirect standard streams to user-specified locations.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1179
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1180
Programs do redirection with the *dup2(2)* system call, or its less-flexible but higher-level stdio analogues, *freopen(3)* and *popen(3)*.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1181
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1182
Redirecting standard input and standard output
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1183
-----------------------------------------------
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1184
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1185
Redirection is usually implemented by placing certain characters between commands. Typically, the syntax of these characters is as follows::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1186
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1187
	$ command1 > file1
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1188
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1189
executes *command1*, placing the output in file1. Note that this will truncate any existing data in *file1*. To append output to the end of the file, use the >> operator.::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1190
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1191
	$ command1 < file1
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1192
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1193
executes *command1*, using *file1* as the source of input (as opposed to the keyboard).::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1194
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1195
	$ command1 < infile > outfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1196
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1197
combines the two capabilities: *command1* reads from *infile* and writes to *outfile*
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1198
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1199
Piping
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1200
-------
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1201
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1202
Programs can be run together such that one program reads the output from another with no need for an explicit intermediate file:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1203
A pipeline of three programs run on a text terminal::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1204
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1205
	$ command1 | command2
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1206
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1207
executes *command1*, using its output as the input for *command2* (commonly called piping, since the "|" character is known as a "pipe").
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1208
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1209
This is equivalent to using two redirects and a temporary file::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1210
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1211
	$ command1 > tempfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1212
	$ command2 < tempfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1213
	$ rm tempfile
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1214
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1215
A good example for command piping is combining *echo* with another command to achieve something interactive in a non-interactive shell, e.g.::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1216
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1217
	$ echo -e "user\npass" | ftp localhost
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1218
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1219
This runs the ftp client with input user, press return, then pass.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1220
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1221
Redirecting to and from the standard file handles
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1222
--------------------------------------------------
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1223
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1224
In Unix shells derived from the original Bourne shell, the first two actions can be further modified by placing a number (the file descriptor) immediately before the character; this will affect which stream is used for the redirection. The Unix standard I/O streams are:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1225
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1226
+------------+-------------+------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1227
|   Handle   |    Name     |      Description       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1228
+============+=============+========================+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1229
| 0          |   stdin     |    Standard input      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1230
+------------+-------------+------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1231
| 1          |   stdout    |    Standard output     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1232
+------------+-------------+------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1233
| 2          |   stderr    |    Standard error      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1234
+------------+-------------+------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1235
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1236
For example:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1237
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1238
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1239
	$ command1 2> file1
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1240
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1241
executes *command1*, directing the standard error stream to *file1*.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1242
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1243
In shells derived from *csh* (the C shell), the syntax instead appends the & character to the redirect characters, thus achieving a similar result.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1244
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1245
Another useful capability is to redirect one standard file handle to another. The most popular variation is to merge standard error into standard output so error messages can be processed together with (or alternately to) the usual output. Example:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1246
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1247
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1248
	$ find / -name .profile > results 2>&1
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1249
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1250
will try to find all files named *.profile*. Executed without redirection, it will output hits to *stdout* and errors (e.g. for lack of privilege to traverse protected directories) to *stderr*. If standard output is directed to file results, error messages appear on the console. To see both hits and error messages in file results, merge *stderr* (handle 2) into *stdout* (handle 1) using 2>&1 .
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1251
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1252
It's possible use 2>&1 before ">" but it doesn't work. In fact, when the interpreter reads 2>&1, it doesn't know yet where standard output is redirected and then standard error isn't merged.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1253
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1254
If the merged output is to be piped into another program, the file merge sequence 2>&1 must precede the pipe symbol, thus:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1255
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1256
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1257
	$ find / -name .profile 2>&1 | less
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1258
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1259
A simplified form of the command:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1260
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1261
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1262
	$ command > file 2>&1
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1263
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1264
is:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1265
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1266
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1267
	$ command &>file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1268
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1269
or:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1270
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1271
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1272
	$command >&file
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1273
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1274
Chained pipelines
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1275
------------------
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1276
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1277
The redirection and piping tokens can be chained together to create complex commands. For example:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1278
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1279
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1280
	$ ls | grep '\.sh' | sort > shlist
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1281
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1282
lists the contents of the current directory, where this output is filtered to only contain lines which contain *.sh*, sort this resultant output lexicographically, and place the final output in *shlist*. This type of construction is used very commonly in shell scripts and batch files.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1283
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1284
Redirect to multiple outputs
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1285
-----------------------------
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1286
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1287
The standard command *tee* can redirect output from a command to several destinations.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1288
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1289
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1290
	$ ls -lrt | tee xyz
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1291
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1292
This directs the file list output to both standard output as well as to the file *xyz*.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1293
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1294
More Text Processing
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1295
====================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1296
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1297
grep
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1298
-----
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1299
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1300
*grep* is a command line text search utility originally written for Unix. The name is taken from the first letters in *global / regular expression / print*, a series of instructions for the *ed* text editor. The *grep* command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1301
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1302
Usage
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1303
~~~~~~
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1304
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1305
This is an example of a common *grep* usage:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1306
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1307
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1308
	$ grep apple fruitlist.txt
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1309
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1310
In this case, *grep* prints all lines containing 'apple' from the file *fruitlist.txt*, regardless of word boundaries; therefore lines containing 'pineapple' or 'apples' are also printed. The *grep* command is case sensitive by default, so this example's output does not include lines containing 'Apple' (with a capital A) unless they also contain 'apple'.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1311
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1312
Like most Unix commands, *grep* accepts command line arguments to change this and many other behaviors. For example:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1313
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1314
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1315
	$ grep -i apple fruitlist.txt
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1316
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1317
This prints all lines containing 'apple' regardless of capitalization. The '-i' argument tells *grep* to be case insensitive, or to ignore case.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1318
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1319
To print all lines containing 'apple' as a word ('pineapple' and 'apples' will not match):
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1320
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1321
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1322
	$ grep -w apple fruitlist.txt
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1323
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1324
Regular expressions can be used to match more complicated queries.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1325
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1326
Variations
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1327
+++++++++++
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1328
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1329
There are countless implementations and derivatives of *grep* available for many operating systems. Early variants of *grep* included *egrep* and *fgrep*. The former applies an extended regular expression syntax that was added to Unix after Ken Thompson's original regular expression implementation. The latter searches for any of a list of 'fixed' strings using the Aho-Corasick algorithm. These variants are embodied in most modern *grep* implementations as command-line switches (and standardized as -E and -F in POSIX). In such combined implementations, *grep* may also behave differently depending on the name by which it is invoked, allowing *fgrep*, *egrep*, and *grep* to be links to the same program.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1330
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1331
*pcregrep* is an implementation of *grep* that uses Perl regular expression syntax.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1332
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1333
Other commands contain the word 'grep' to indicate that they search (usually for regular expression matches). The *pgrep* utility, for instance, displays the processes whose names match a given regular expression.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1334
74
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1335
tr
7dbeae0fac70 Removed numbering for sections
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 73
diff changeset
  1336
--
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1337
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1338
*tr* (abbreviated from *translate* or *transliterate*) is a command in Unix-like operating systems.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1339
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1340
When executed, the program reads from the standard input and writes to the standard output. It takes as parameters two sets of characters, and replaces occurrences of the characters in the first set with the corresponding elements from the other set. For example,
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1341
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1342
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1343
	$ tr 'abcd' 'jkmn' 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1344
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1345
maps 'a' to 'j', 'b' to 'k', 'c' to 'm', and 'd' to 'n'.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1346
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1347
Sets of characters may be abbreviated by using character ranges. The previous example could be written:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1348
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1349
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1350
	$ tr 'a-d' 'jkmn'
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1351
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1352
In POSIX compliant versions of *tr* the set represented by a character range depends on the locale's collating order, so it is safer to avoid character ranges in scripts that might be executed in a locale different from that in which they were written. Ranges can often be replaced with POSIX character sets such as [:alpha:].
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1353
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1354
The *-c* flag complements the first set of characters.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1355
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1356
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1357
	$ tr -cd '[:alnum:]' 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1358
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1359
therefore removes all non-alphanumeric characters.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1360
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1361
The *-s* flag causes tr to compress sequences of identical adjacent characters in its output to a single token. For example,
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1362
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1363
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1364
	$ tr -s '\n' '\n'
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1365
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1366
replaces sequences of one or more newline characters with a single newline.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1367
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1368
The *-d* flag causes tr to delete all tokens of the specified set of characters from its input. In this case, only a single character set argument is used. The following command removes carriage return characters, thereby converting a file in DOS/Windows format to one in Unix format.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1369
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1370
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1371
	$ tr -d '\r'
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1372
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1373
Most versions of *tr*, including GNU *tr* and classic Unix *tr*, operate on single byte characters and are not Unicode compliant. An exception is the Heirloom Toolchest implementation, which provides basic Unicode support.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1374
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1375
Ruby and Perl also have an internal *tr* operator, which operates analogously. Tcl's *string map* command is more general in that it maps strings to strings while *tr* maps characters to characters.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1376
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1377
Elementary Regex
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1378
=================
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1379
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1380
In computing, regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters. A regular expression (often shortened to regex or regexp) is written in a formal language that can be interpreted by a regular expression processor, a program that either serves as a parser generator or examines text and identifies parts that match the provided specification.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1381
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1382
Regular expressions are used by many text editors, utilities, and programming languages to search and manipulate text based on patterns. For example, Perl, Ruby and Tcl have a powerful regular expression engine built directly into their syntax. Several utilities provided by Unix distributions—including the editor *ed* and the filter *grep* — were the first to popularize the concept of regular expressions.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1383
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
  1384
Traditional Unix regular expression syntax followed common conventions but often differed from tool to tool. The IEEE POSIX *Basic Regular Expressions* (BRE) standard (released alongside an alternative flavor called Extended Regular Expressions or ERE) was designed mostly for backward compatibility with the traditional (Simple Regular Expression) syntax but provided a common standard which has since been adopted as the default syntax of many Unix regular expression tools, though there is often some variation or additional features. Many such tools also provide support for ERE syntax with command line arguments.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1385
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1386
In the BRE syntax, most characters are treated as literals — they match only themselves (i.e., a matches "a"). The exceptions, listed below, are called metacharacters or metasequences.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1387
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1388
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1389
|Metacharacter|                            Description                     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1390
+=============+============================================================+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1391
| .           | Matches any single character (many applications exclude    | 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1392
|             | newlines, and exactly which characters are considered      | 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1393
|             | newlines is flavor, character encoding, and platform       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1394
|             | specific, but it is safe to assume that the line feed      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1395
|             | character is included). Within POSIX bracket expressions,  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1396
|             | the dot character matches a literal dot. For example, a.c  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1397
|             | matches abc, etc., but [a.c] matches only a, ., or         |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1398
|             | c.                                                         |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1399
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1400
| [ ]         | A bracket expression. Matches a single character that is   | 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1401
|             | contained within the brackets. For example, [abc] matches  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1402
|             | a, b, or c. [a-z] specifies a range which matches any      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1403
|             | lowercase letter from a to z. These forms can be mixed:    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1404
|             | [abcx-z] matches a, b, c, x, y, or z, as does              |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1405
|             | [a-cx-z]. The - character is treated as a literal character|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1406
|             | if it is the last or the first character within the        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1407
|             | brackets, or if it is escaped with a backslash: [abc-],    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1408
|             | [-abc], or [a\-bc].                                        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1409
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1410
| [^ ]        | Matches a single character that is not contained within the|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1411
|             | brackets. For example, [^abc] matches any character other  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1412
|             | than a, b, or c. [^a-z] matches any single character       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1413
|             | that is not a lowercase letter from a to z. As above,      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1414
|             | literal characters and ranges can be mixed.                |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1415
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1416
| ^           | Matches the starting position within the string. In        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1417
|             | line-based tools, it matches the starting position of any  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1418
|             | line.                                                      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1419
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1420
| $           | Matches the ending position of the string or the position  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1421
|             | just before a string-ending newline. In line-based tools,  |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1422
|             | it matches the ending position of any line.                |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1423
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1424
| `*`         | Matches the preceding element zero or more times. For      |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1425
|             | example, ab*c matches "ac", "abc", "abbbc", etc. [xyz]*    |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1426
|             | matches "", "x", "y", "z", "zx", "zyx", "xyzzy", and so on.|
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1427
|             | \(ab\)* matches "", "ab", "abab", "ababab", and so on.     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1428
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1429
| ?           | Matches the preceding element zero or one time. For        |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1430
|             | example, ba? matches "b" or "ba".                          |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1431
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1432
| `+`         | Matches the preceding element one or more times. For       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1433
|             | example, ba+ matches "ba", "baa", "baaa", and so on.       |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1434
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1435
| `|`         | The choice (aka alternation or set union) operator matches |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1436
|             | either the expression before or the expression after the   |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1437
|             | operator. For example, abc|def matches "abc" or "def".     |
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1438
+-------------+------------------------------------------------------------+
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1439
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1440
Lazy quantification
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1441
--------------------
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1442
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1443
The standard quantifiers in regular expressions are greedy, meaning they match as much as they can, only giving back as necessary to match the remainder of the regex. For example, someone new to regexes wishing to find the first instance of an item between < and > symbols in this example:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1444
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1445
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1446
	Another whale explosion occurred on <January 26>, <2004>.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1447
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1448
...would likely come up with the pattern <.*>, or similar. However, this pattern will actually return "<January 26>, <2004>" instead of the "<January 26>" which might be expected, because the `*` quantifier is greedy — it will consume as many characters as possible from the input, and "January 26>, <2004" has more characters than "January 26".
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1449
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
  1450
Though this problem can be avoided in a number of ways (e.g., by specifying the text that is not to be matched: <[^>]*>), modern regular expression tools allow a quantifier to be specified as *lazy* (also known as non-greedy, reluctant, minimal, or ungreedy) by putting a question mark after the quantifier (e.g., <.*?>), or by using a modifier which reverses the greediness of quantifiers (though changing the meaning of the standard quantifiers can be confusing). By using a lazy quantifier, the expression tries the minimal match first. Though in the previous example lazy matching is used to select one of many matching results, in some cases it can also be used to improve performance when greedy matching would require more backtracking.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1451
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1452
One Liners
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1453
===========
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1454
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1455
A *one-liner* is textual input to the command-line of an operating system shell that performs some function in just one line of input.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1456
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1457
The one liner can be
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1458
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1459
   1. An expression written in the language of the shell.
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
  1460
   2. The invocation of an interpreter together with program source for the interpreter to run.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1461
   3. The invocation of a compiler together with source to compile and 	  
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1462
      instructions for executing the compiled program.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1463
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1464
Certain dynamic scripting languages such as AWK, sed, and perl have traditionally been adept at expressing one-liners. Specialist shell interpreters such as these Unix shells or the Windows PowerShell, allow for the construction of powerful one-liners.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1465
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1466
The use of the phrase one-liner has been widened to also include program-source for any language that does something useful in one line.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1467
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1468
The word *One-liner* has two references in the index of the book *The AWK Programming Language* (the book is often referred to by the abbreviation TAPL). It explains the programming language AWK, which is part of the Unix operating system. The authors explain the birth of the One-liner paradigm with their daily work on early Unix machines:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1469
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1470
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1471
    “The 1977 version had only a few built-in variables and predefined functions. It was designed for writing short programs [...] Our model was that an invocation would be one or two lines long, typed in and used immediately. Defaults were chosen to match this style [...] We, being the authors, knew how the language was supposed to be used, and so we only wrote one-liners.”
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1472
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1473
Notice that this original definition of a One-liner implies immediate execution of the program without any compilation. So, in a strict sense, only source code for interpreted languages qualifies as a One-liner. But this strict understanding of a One-liner was broadened in 1985 when the IOCCC introduced the category of Best One Liner for C, which is a compiled language.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1474
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1475
The TAPL book contains 20 examples of One-liners (A Handful of Useful awk One-Liners) at the end of the book's first chapter.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1476
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
  1477
Here are the first few of them:
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1478
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1479
   1. Print the total number of input lines:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1480
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1481
      END { print NR }
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1482
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1483
   2. Print the tenth input line:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1484
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1485
      NR == 10
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1486
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1487
   3. Print the last field of every input line:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1488
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1489
      { print $NF }
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1490
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1491
One-liners are also used to show off the differential expressive power of programming languages. Frequently, one-liners are used to demonstrate programming ability. Contests are often held to see who can create the most exceptional one-liner.
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1492
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1493
The following example is a C program (a winning entry in the "Best one-liner" category of the IOCCC, here split to two lines for presentation).::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1494
	
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1495
	main(int c,char**v){return!m(v[1],v[2]);}m(char*s,char*t){return
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1496
	*t-42?*s?63==*t|*s==*t&&m(s+1,t+1):!*t:m(s,t+1)||*s&&m(s+1,t);}
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1497
73
d32a19958ad9 Completed first review and cuts of ULT
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 55
diff changeset
  1498
This one-liner program is a *glob pattern matcher*. It understands the glob characters '*' meaning 'zero or more characters' and '?' meaning exactly one character, just like most Unix shells.
55
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1499
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1500
Run it with two args, the string and the glob pattern. The exit status is 0 (shell true) when the pattern matches, 1 otherwise. The glob pattern must match the whole string, so you may want to use * at the beginning and end of the pattern if you are looking for something in the middle. Examples::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1501
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1502
	$ prog foo 'f??'; echo $?
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1503
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1504
	$ prog 'best short program' '??st*o**p?*'; echo $?
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1505
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1506
Here is a one line shell script to show directories:
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1507
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1508
::
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1509
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1510
	$ ls -R | grep ":$" | sed -e 's/:$//' -e 's/[^-][^\/]*\//--/g' -e 's/^/   /' -e 's/-/|/' 
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1511
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1512
6aa9568b5874 Completed rough draft of first three sessions in module one.
Kadambari Devarajan <kadambari.devarajan@gmail.com>
parents: 44
diff changeset
  1513