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     1 ===============
       
     2 Version Control
       
     3 ===============
       
     4 
       
     5 Introduction
       
     6 ============
       
     7 
       
     8 The following words are from a blogpost "http://karlagius.com/2009/01/09/version-control-for-the-masses/"
       
     9 
       
    10 "Version control is one of those weird, geeky things that never really gained much ground in non-geek fields, despite the fact that it’s blindingly useful.
       
    11 
       
    12 Version control (or source control) is nothing more arcane than keeping copies of ones work as one make changes to it. On the surface, it’s all straight-forward; make a copy of every file before making any changes to it. That way, if something seriously messes up, one can always fall back to something that worked before, or at least compare the broken copy with one that used to work so one can figure out where it went off kilter. Accidentally deleted half of thesis and closed the word processor? No problem – out comes the backup."
       
    13 
       
    14 Now, in the real world, it’s not so easy. One probably cooks up their own version control system without realizing it had such a geeky name. For instances files with names oldxxxxxx.py and latestxxxxxx.py. Every time to make some change in a file, one save it with different name then the original one. Luckily there are like, loads of version control systems out there to do this heavy lifting.
       
    15 
       
    16 Why Use Version Control
       
    17 =======================
       
    18  
       
    19 One of idea behind Version Control Tools was to build onto very first step which can be creating a empty file, or writing a first buggy program for assignment, rather then simply loose it. So here are some reasons why is automated version control needed:
       
    20 
       
    21     - It will track the history and evolution of a project, so one don't have to do it manually. It allows to track what changes where made, when were they made, by whom and why.
       
    22     - For a team of people working on same project, revision control software makes it easier to collaborate. For example, when people more or less simultaneously make potentially incompatible changes, the software will help them to identify and resolve those conflicts.
       
    23     - It can help to recover from mistakes. If a change made at some moment of time, turns out to be in error in future, one can revert to an earlier version of one or more files. In fact, a really good revision control tool will even help in efficiently figure out exactly when a problem was introduced.
       
    24 
       
    25 Most of these reasons are equally valid for the project having one man show, or hundred people. Besides projects, even it can be used to maintain assignments related to one particular subject/course, it will help manage things in way much better way. These tools can be used for better *resources management*. All codes, documents, presentation, assignments related to one course maintained in such a inventory can help avoiding accidental lose of data(deletion) and Internet hosting for version control will make the work immune to local hard-disk crash, unless hosting crashes itself.
       
    26 
       
    27 Some of Version Control Tools available and used widely are:
       
    28 
       
    29      - cvs (Concurrent Version System)
       
    30      - svn (Subversion)
       
    31      - hg (Mercurial)
       
    32      - bzr (Bazaar)
       
    33      - git 
       
    34 
       
    35 Each of above mentioned tools have sets of feature which it offers in unique way. For this session we are going to concentrate on hg (mercurial). After covering the basics of hg, one can easily try other tools, and use what-ever he/she is most comfortable with.
       
    36 
       
    37 Learning the Lingo
       
    38 ==================
       
    39 
       
    40 Each Version Control uses its own nomenclature for more or less the same features. Here are some of terms which are going to used through out the rest of session:
       
    41 
       
    42 Basic Setup
       
    43 -----------
       
    44 
       
    45      Repository(repo):
       
    46 	The database/folder storing the files.
       
    47      Server:
       
    48 	The computer storing the repo.
       
    49      Client:
       
    50 	The computer connecting to the repo.
       
    51      Working Set/Working Copy:
       
    52      	Your local directory of files, where you make changes. This is what is present on client side.
       
    53      Trunk/Main:
       
    54 	The “primary” location for code in the repo. Think of code as a family tree — the “trunk” is the main line. This is generally what is present on server.
       
    55 
       
    56 Basic Actions
       
    57 -------------
       
    58      
       
    59      Add:
       
    60 	Put a file into the repo for the first time, i.e. begin tracking it with Version Control.
       
    61      Revision:
       
    62 	What version a file is on.
       
    63      Head/Tip:
       
    64 	The latest revision of the repo.
       
    65      Check out:
       
    66      	Initial download of repo onto machine.
       
    67      Commit:
       
    68      	Upload a file to repository(if it has changed). The file gets a new revision number, and people can “check out” the latest one.
       
    69      Checking Message:
       
    70      	A short message describing what was changed.
       
    71      Change log/History:
       
    72 	A list of changes made to a file since it was created.
       
    73      Update/Sync:
       
    74 	Synchronize local files with the latest from the repository on server. This get the latest revisions of all files.
       
    75      Revert:
       
    76 	Throw away the local changes and reload the latest version from the repository.
       
    77 
       
    78 Advanced Actions:
       
    79 -----------------
       
    80 
       
    81      Branch:
       
    82 	Create a separate copy of a file/folder for private use (bug fixing, testing, etc).
       
    83      Diff/Change:
       
    84 	Finding the differences between two files. Useful for seeing what changed between revisions.
       
    85      Merge (or patch):
       
    86      	Apply the changes from one file to another, to bring it up-to-date.
       
    87      Conflict:
       
    88 	When pending changes to a file contradict each other (both changes cannot be applied).
       
    89      Resolve:
       
    90 	Fixing the changes that contradict each other and checking in the correct version.
       
    91      
       
    92 Types of Version Control:
       
    93 -------------------------
       
    94 
       
    95 Based on how source/code management is carried out in a tool there are two categories of Version Control Systems(VCS):
       
    96 
       
    97       - Centralized VCS: 
       
    98       	In this kind of system all the revision control functions are performed on a shared server. If two developers try to change the same file at the same time, without some method of managing access the developers may end up overwriting each other's work. Centralized revision control systems solve this problem in one of two different "source management models": file locking and version merging. Both svn and cvs follows this kind of management.
       
    99    
       
   100       - Distributed VCS:
       
   101       	In a distributed model, every developer has their own repo. Diffs, commits, and reverts are all done locally, one needs Internet only to share the changes with others. It makes work faster, handles branching and merging in better way, with less management. hg, bzr and git uses this work flow.
       
   102 
       
   103 Get Going with Hg:
       
   104 ==================
       
   105 
       
   106 Why hg?
       
   107 -------
       
   108 
       
   109 	- It is easy to learn and use.
       
   110 	- It is lightweight.
       
   111 	- It scales excellently.
       
   112 	- It is based on Python.
       
   113 
       
   114 A small point to notice here, hg cant track binary files for changes, one can add them to repo, but wont be able to track changes made to it. And hg considers, odt, pdf files as binary.
       
   115 
       
   116 Getting Started:
       
   117 ----------------
       
   118 
       
   119 Following command tells the version of hg installed on machine: ::
       
   120    
       
   121    $hg version
       
   122 
       
   123    Mercurial Distributed SCM (version 1.1.2)
       
   124    Copyright (C) 2005-2008 Matt Mackall <mpm@selenic.com> and others
       
   125    This is free software; see the source for copying conditions. There is NO
       
   126    warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       
   127 
       
   128 Built-in help, Mercurial provides a built-in help system. Following command will print a brief list of commands, along with a description of what each does. ::
       
   129 
       
   130    $hg help
       
   131 
       
   132    Mercurial Distributed SCM
       
   133    list of commands:
       
   134    add          add the specified files on the next commit
       
   135    addremove	-----------------------
       
   136 
       
   137 For specific command, just follow the command name after the help. ::
       
   138 
       
   139     $hg help diff
       
   140     hg diff [OPTION]... [-r REV1 [-r REV2]] [FILE]...
       
   141 
       
   142     diff repository (or selected files)
       
   143     Show differences between revisions for the specified files.
       
   144     Differences between files are shown using the unified diff format.
       
   145     NOTE:____________
       
   146 
       
   147 Let there be Repository:
       
   148 ------------------------
       
   149 
       
   150 In Mercurial, everything happens inside a repository. The repository for a project contains all of the files that “belong to” that project, along with a historical record of the project's files. A repository is simply a directory tree in file-system that Mercurial treats as special.
       
   151 
       
   152 There can be two ways to create a repo, either getting local copy for existing repo available on Internet or machine, or creating a new repo. For getting already existing repo hg uses command *"clone"* ::
       
   153 
       
   154       $hg clone http://hg.serpentine.com/tutorial/hello localCopyhello
       
   155 
       
   156       requesting all changes
       
   157       adding changesets
       
   158       adding manifests
       
   159       adding file changes
       
   160       added 5 changesets with 5 changes to 2 files
       
   161       updating working directory
       
   162       2 files updated, 0 files merged, 0 files removed, 0 files unresolved
       
   163 
       
   164 If clone succeeded, there would be a local directory called localCopyhello, with some files: ::
       
   165 
       
   166       $ls localCopyhello/
       
   167       hello.c  Makefile
       
   168 
       
   169 Every Mercurial repository is complete, self-contained, and independent. It contains its own private copy of a project's files and history.
       
   170 
       
   171 To start a new repository use *hg init*: ::
       
   172 
       
   173    $ mkdir Fevicol
       
   174    $ cd Fevicol/
       
   175    $ echo "print 'Yeh Fevicol ka Majboot jod hai'" > feviStick.py
       
   176    $ ls -a
       
   177    .  ..  feviStick.py
       
   178    $ hg init
       
   179    $ ls -a
       
   180    .  ..  feviStick.py  .hg
       
   181 
       
   182 *.hg* directory indicates that this new dir is now a repo.This is where Mercurial keeps all of its metadata for the repository.The contents of the .hg directory and its subdirectories are private to Mercurial. Rest all files are for the user to use them as they pleases.
       
   183 
       
   184 Creating a branch of existing local repo is very easy via hg using clone command: ::
       
   185 	
       
   186     $ hg clone localCopyhello newCopy
       
   187     updating working directory
       
   188     2 files updated, 0 files merged, 0 files removed, 0 files unresolved
       
   189 
       
   190 newCopy is exact copy of already existing repo. And this command can be used to create branch of locally created repo also: ::
       
   191 
       
   192     $ hg clone Fevicol Fevicol-pull
       
   193     updating working directory
       
   194     0 files updated, 0 files merged, 0 files removed, 0 files unresolved
       
   195 
       
   196 These local branches can prove really handy at times. It allows keep multiple copies of local branch for different purposes, say for debugging, testing, working version.
       
   197 	
       
   198 History or Logs:
       
   199 ----------------
       
   200 
       
   201 For the new repo created, first thing which can be tried is to check the logs/history. What changes were made and when and why, answers to all those questions are stored in logs safely. So for the the cloned repo the history can be viewed using command *"log"* (following commands are wrt localCopyhello repo). ::
       
   202 
       
   203     $hg log
       
   204     changeset:   4:2278160e78d4
       
   205     tag:         tip
       
   206     user:        Bryan O'Sullivan <bos@serpentine.com>
       
   207     date:        Sat Aug 16 22:16:53 2008 +0200
       
   208     summary:     Trim comments.
       
   209 
       
   210     changeset:   3:0272e0d5a517
       
   211     user:        Bryan O'Sullivan <bos@serpentine.com>
       
   212     date:        Sat Aug 16 22:08:02 2008 +0200
       
   213     summary:     Get make to generate the final binary from a .o file.
       
   214 
       
   215     changeset:   2:fef857204a0c
       
   216     user:        Bryan O'Sullivan <bos@serpentine.com>
       
   217     date:        Sat Aug 16 22:05:04 2008 +0200
       
   218     summary:     Introduce a typo into hello.c.
       
   219 
       
   220     changeset:   1:82e55d328c8c
       
   221     user:        mpm@selenic.com
       
   222     date:        Fri Aug 26 01:21:28 2005 -0700
       
   223     summary:     Create a makefile
       
   224 
       
   225     changeset:   0:0a04b987be5a
       
   226     user:        mpm@selenic.com
       
   227     date:        Fri Aug 26 01:20:50 2005 -0700
       
   228     summary:     Create a standard "hello, world" program
       
   229 
       
   230 By default, this command prints a brief paragraph of output for each change to the project that was recorded.The fields in a record of output from hg log are as follows:
       
   231 
       
   232    - changeset: This field has the format of a number, followed by a colon, followed by a hexadecimal (or hex) string. These are identifiers for the changeset. The hex string is a unique identifier: the same hex string will always refer to the same changeset in every copy of this repository. 
       
   233    - user: The identity of the person who created the changeset.
       
   234    - date: The date and time on which the changeset was created, and the timezone in which it was created.
       
   235    - summary: The first line of the text message that the creator of the changeset entered to describe the changeset.
       
   236    - tag: A tag is another way to identify a changeset, by giving it an easy-to-remember name.
       
   237 
       
   238 To narrow the output of hg log down to a single revision, use the -r (or --rev) option. ::
       
   239    
       
   240    $hg log -r 3
       
   241    changeset:   3:0272e0d5a517
       
   242    user:        Bryan O'Sullivan <bos@serpentine.com>
       
   243    date:        Sat Aug 16 22:08:02 2008 +0200
       
   244    summary:     Get make to generate the final binary from a .o file.
       
   245 
       
   246 *range notation* can be used to get history of several revisions without having to list each one. ::
       
   247 
       
   248    $ hg log -r 2:4
       
   249    changeset:   2:fef857204a0c
       
   250    user:        Bryan O'Sullivan <bos@serpentine.com>
       
   251    date:        Sat Aug 16 22:05:04 2008 +0200
       
   252    summary:     Introduce a typo into hello.c.
       
   253 
       
   254    changeset:   3:0272e0d5a517
       
   255    user:        Bryan O'Sullivan <bos@serpentine.com>
       
   256    date:        Sat Aug 16 22:08:02 2008 +0200
       
   257    summary:     Get make to generate the final binary from a .o file.
       
   258 
       
   259    changeset:   4:2278160e78d4
       
   260    tag:         tip
       
   261    user:        Bryan O'Sullivan <bos@serpentine.com>
       
   262    date:        Sat Aug 16 22:16:53 2008 +0200
       
   263    summary:     Trim comments.
       
   264 
       
   265 The hg log  command's -v (or --verbose) option gives you this extra detail. ::
       
   266 
       
   267     $ hg log -v -r 3
       
   268     changeset:   3:0272e0d5a517
       
   269     user:        Bryan O'Sullivan <bos@serpentine.com>
       
   270     date:        Sat Aug 16 22:08:02 2008 +0200
       
   271     files:       Makefile
       
   272     description:
       
   273     Get make to generate the final binary from a .o file.
       
   274 
       
   275 Making Changes:
       
   276 ---------------
       
   277 
       
   278 There is feviStick.py file in repo created above with name Fevicol. *status(alias st)* command prints the revision history of the specified files or the entire project::
       
   279 
       
   280     $ cd Fevicol
       
   281     $ hg log
       
   282     $ hg status
       
   283     ? feviStick.py
       
   284 
       
   285 "?" sign in front of file indicates that this file is not yet part of track record. *add* command is used to add new files to repo. ::
       
   286 
       
   287     $ hg add feviStick.py
       
   288     $ hg st
       
   289     A feviStick.py
       
   290 
       
   291 So file is now part of repository(A symbol). Use *commit (alias ci)* command to make changes effective(this command would be explained in more details in later parts). ::
       
   292    
       
   293    $ hg ci -u "Shantanu <shantanu@fossee.in>" -m "First commit."
       
   294    $ hg log
       
   295    changeset:   0:84f5e91f4de1
       
   296    tag:         tip
       
   297    user:        Shantanu <shantanu@fossee.in>
       
   298    date:        Fri Aug 21 23:37:13 2009 +0530
       
   299    summary:     First commit.
       
   300 
       
   301 Similar to add there are other commands available for file management in repo. *copy (alias cp)* command is used to mark files as copied for the next commit. ::
       
   302 
       
   303    $ hg cp feviStick.py pidiLite.py
       
   304    $ hg st
       
   305    A pidiLite.py
       
   306 
       
   307 *rename(alias mv)* rename files; equivalent of copy + remove. *tip* command shows newest revision in the repository. ::
       
   308 
       
   309    $ hg rename pidiLite.py feviCol.py
       
   310    $ hg st
       
   311    A feviCol.py
       
   312    $ hg ci -u "Shantanu <shantanu@fossee.in>" -m "Renamed pidiLite.py."
       
   313    $ hg tip
       
   314    changeset:   1:d948fb4137c5
       
   315    tag:         tip
       
   316    user:        Shantanu <shantanu@fossee.in>
       
   317    date:        Sat Aug 22 00:11:25 2009 +0530
       
   318    summary:     Renamed pidiLite.py.
       
   319 
       
   320 *remove* command is used to remove files from a repo. ::
       
   321 
       
   322    $ hg remove feviCol.py
       
   323    $ hg st
       
   324    R feviCol.py
       
   325 
       
   326 R status of files denotes, file is marked as to be removed by the previous command *remove*. To add the file again to repo, one can use *revert* command, which restore individual files or dirs to an earlier state. ::
       
   327 
       
   328   $ ls
       
   329   feviStick.py
       
   330   $ hg revert feviCol.py
       
   331   $ ls
       
   332   feviCol.py  feviStick.py
       
   333 
       
   334 Sharing Changes:
       
   335 ----------------
       
   336 
       
   337 Pulling from repo:
       
   338 ~~~~~~~~~~~~~~~~~~
       
   339 
       
   340 As mentioned earlier that repositories in Mercurial are self-contained. This means that the changeset just created exists only in Fevicol repository and not in previously cloned Fevicol-pull. There are a few ways that can be used to propagate this change into other repositories. ::
       
   341 
       
   342    $ hg clone Fevicol Fevicol-clone
       
   343    updating working directory
       
   344    2 files updated, 0 files merged, 0 files removed, 0 files unresolved
       
   345 
       
   346 Or traverse into the any dir which is a working hg repo(using hg init) and pull command will download all changeset from main repo. ::
       
   347 
       
   348    $ mkdir Fevicol-pull
       
   349    $ cd Fevicol-pull
       
   350    $ hg init
       
   351    $ hg pull ../Fevicol
       
   352    pulling from ../Fevicol
       
   353    requesting all changes
       
   354    adding changesets
       
   355    adding manifests
       
   356    adding file changes
       
   357    added 2 changesets with 2 changes to 2 files
       
   358    (run 'hg update' to get a working copy)
       
   359 
       
   360 *changeset* means a list of changes made to a file. In words of *hg help*, pull command is: ::
       
   361 
       
   362    pull changes from the specified source
       
   363 
       
   364     Pull changes from a remote repository to a local one.
       
   365 
       
   366     This finds all changes from the repository at the specified path
       
   367     or URL and adds them to the local repository. By default, this
       
   368     does not update the copy of the project in the working directory.
       
   369 
       
   370 Some times, even before pulling changesets, one may need to see what changes would be pulled, Mercurial provides *hg incoming* to tell what changes *hg pull* would pull into repo, without actually pulling the changes. This command is really handy in case of avoiding unwanted changesets into the repo.
       
   371 
       
   372 With Mercurial, *hg pull* does not(by default) touch the working directory. Instead there is *hg up (alias update, co, checkout)* command to do this. ::
       
   373 
       
   374     $ cd Fevicol-pull
       
   375     $ ls -a
       
   376     .  ..  .hg
       
   377     $ hg up
       
   378     2 files updated, 0 files merged, 0 files removed, 0 files unresolved
       
   379     $ ls -a
       
   380     .  ..  feviCol.py  feviStick.py  .hg
       
   381     
       
   382 To update to specific version, give a version number to the *hg update* command. ::
       
   383    
       
   384     $ hg update 0
       
   385     0 files updated, 0 files merged, 1 files removed, 0 files unresolved
       
   386     $ hg parent
       
   387     changeset:   0:84f5e91f4de1
       
   388     user:        Shantanu <shantanu@fossee.in>
       
   389     date:        Fri Aug 21 23:37:13 2009 +0530
       
   390     summary:     First commit.
       
   391 
       
   392 If no version number is specified *hg up* will update to the tip version. Version number of hg starts from 0. Compare *hg parent* output to the one before doing update to see the difference.
       
   393 
       
   394 Making Changes:
       
   395 ~~~~~~~~~~~~~~~
       
   396 
       
   397 After getting the desired version of local repo, one can make changes as he/she needs and then make them available(share) for others. For these operations we will be working in Fevicol-clone repo which we created earlier. It's often good practice to keep a “pristine” copy of a remote repository around, which you can then make temporary clones of to create sandboxes for each task you want to work on. ::
       
   398 
       
   399     $ cd Fevicol-clone/
       
   400     $ cat feviStick.py 
       
   401     print 'Yeh Fevicol ka Majboot jod hai'
       
   402 
       
   403 This tagline is correct for feviCol.py but for feviStick.py it should be different. ::
       
   404 
       
   405     $ echo "print 'Ab no more Chip Chip'" > feviStick.py
       
   406     $ cat feviStick.py
       
   407     print 'Ab no more Chip Chip'
       
   408     $ hg st
       
   409     M feviStick.py
       
   410 
       
   411 Mercurial's hg status command will tell us what Mercurial knows about the files in the repository. 'M' sign in front of feviStick.py indicates that Mercurial has noticed change.
       
   412 
       
   413 It's somewhat helpful to know that feviStick.py was modified, but one might prefer to know exactly what changes were made to it. To do this, use the *hg diff* command. ::
       
   414 
       
   415     $ hg diff
       
   416     diff -r a7912d45f47c feviStick.py
       
   417     --- a/feviStick.py	 Sun Aug 23 22:34:35 2009 +0530
       
   418     +++ b/feviStick.py	 Sun Aug 23 22:47:49 2009 +0530
       
   419     @@ -1,1 +1,1 @@
       
   420     -print 'Yeh Fevicol ka Majboot jod hai'
       
   421     +print 'Ab no more Chip Chip'
       
   422 
       
   423 We can modify files, build and test our changes, and use hg status and hg diff to review our changes, until we're satisfied with what we've done and arrive at a natural stopping point where we want to record our work in a new changeset. All the diffs prior to committing the changes would be done wrt earlier marked record.The hg commit command lets us create a new changeset.
       
   424 
       
   425 Mercurial records your name and address with each change that you commit, so that you and others will later be able to tell who made each change. Mercurial tries to automatically figure out a sensible username to commit the change with. When we try to use *hg commit* there are various ways by which one can specify User name, some of those are:
       
   426 	  
       
   427 	  - Specify a -u option to the hg commit command on the command line, followed by a username.
       
   428 	  - set HGUSER environment variable.
       
   429 	  - Edit hgrc file present in .hg folder to set this property, add following lines to that file and Mercurial will read those parameters from that location. ::
       
   430 	  
       
   431 		[ui]
       
   432 		username = Firstname Lastname <email.address@example.net>
       
   433 
       
   434 For me the hgrc file looks like this: ::
       
   435 
       
   436     [paths]
       
   437     default = /home/baali/Fevicol
       
   438     [ui]
       
   439     username = Shantanu Choudhary <shantanu@fossee.in>
       
   440 
       
   441 Once this parameter is set, *hg commit* command drops us into a text editor, to enter a message that will describe the modifications we've made in this changeset. This is called the commit message. It will be a record for readers of what we did and why, and it will be printed by hg log after we've finished committing. ::
       
   442 
       
   443     Changed tagline for feviStick.py.
       
   444     HG: Enter commit message.  Lines beginning with 'HG:' are removed.
       
   445     HG: --
       
   446     HG: user: Shantanu Choudhary <shantanu@fossee.in>
       
   447     HG: branch 'default'
       
   448     HG: changed feviStick.py 
       
   449 
       
   450 This would be your default system editor(for me it is vim, one can set it also), where you can enter the log message in first line, once you are done with log message quit the editor using *[ESC] key ":wq"*.Once we've finished the commit, we can use the hg tip command to display the changeset we just created. ::
       
   451 
       
   452     $ hg tip
       
   453     changeset:   3:e1ab2aff4ddd
       
   454     tag:         tip
       
   455     user:        Shantanu Choudhary <shantanu@fossee.in>
       
   456     date:        Sun Aug 23 23:32:01 2009 +0530
       
   457     summary:     Changed tagline for feviStick.py. 
       
   458 
       
   459 One can do above mentioned procedure using following one line command: ::
       
   460 
       
   461     $ hg ci -u "Shantanu <shantanu@fossee.in>" -m "Changed tagline for feviStick.py."
       
   462 
       
   463 Sharing Changes:
       
   464 ~~~~~~~~~~~~~~~~
       
   465 
       
   466 The *hg outgoing* command tells us what changes would be pushed into another repository. ::
       
   467 
       
   468     $ hg outgoing ../Fevicol
       
   469     comparing with ../Fevicol
       
   470     searching for changes
       
   471     changeset:   3:e1ab2aff4ddd
       
   472     tag:         tip
       
   473     user:        Shantanu Choudhary <shantanu@fossee.in>
       
   474     date:        Sun Aug 23 23:32:01 2009 +0530
       
   475     summary:     Changed tagline for feviStick.py.
       
   476 
       
   477 And the *hg push* command does the actual push. ::
       
   478 
       
   479     $ hg push ../Fevicol
       
   480     pushing to ../Fevicol
       
   481     searching for changes
       
   482     adding changesets
       
   483     adding manifests
       
   484     adding file changes
       
   485     added 1 changesets with 1 changes to 1 files
       
   486 
       
   487 As with hg pull, the hg push command does not update the working directory in the repository that it's pushing changes into. One has to use hg update to populate the changes in desired repo. ::
       
   488 
       
   489    $ cd ../Fevicol
       
   490    $ hg tip
       
   491    changeset:   3:e1ab2aff4ddd
       
   492    tag:         tip
       
   493    user:        Shantanu Choudhary <shantanu@fossee.in>
       
   494    date:        Sun Aug 23 23:32:01 2009 +0530
       
   495    summary:     Changed tagline for feviStick.py.
       
   496    $ cat feviStick.py
       
   497    print 'Yeh Fevicol ka Majboot jod hai'
       
   498 
       
   499 changesets are imported, but update is yet to be done. ::
       
   500 
       
   501    $ hg up tip
       
   502    1 files updated, 0 files merged, 0 files removed, 0 files unresolved
       
   503    $ $ cat feviStick.py 
       
   504    print 'Ab no more Chip Chip'
       
   505 
       
   506 Merging the Work:
       
   507 ~~~~~~~~~~~~~~~~~
       
   508 
       
   509 This is next aspect of any version control, how to merge work done by various participants of project in a way that no one looses changes being made, and still remains updated. Here is simple case study which can help understanding why merging is required: 
       
   510 
       
   511 Two persons, A and B are contributing on same project. Both starts from cloning the same online repo(lets say present state X), so that both have a working local repo. Now A edits one of file, commits the changes and pushes to the repo, hence changing the state of repo to Y, but B, have not updated his repo, makes a change in one of files and reaches to a different state Z. Now when A pulls repo from B, his repo will have multiple heads. This stage is clearly ambiguous, the repo of A is not consistent, it has multiple heads, and from here, whatever changes he makes can take whatsoever direction if it is not fixed, and hence A will have to merge changes so that everything becomes consistent again.
       
   512 
       
   513 Lets see how this work with working repo, we will use Fevicol and Fevicol-clone repositories created earlier. For now, the status of both repo is: ::
       
   514 
       
   515     $ cd Fevicol-clone
       
   516     $ hg tip
       
   517     changeset:   3:e1ab2aff4ddd
       
   518     tag:         tip
       
   519     user:        Shantanu Choudhary <shantanu@fossee.in>
       
   520     date:        Sun Aug 23 23:32:01 2009 +0530
       
   521     summary:     Changed tagline for feviStick.py.
       
   522 
       
   523 The tagline for feviCol.py is not complete, so we make changes in that file in this repo. ::
       
   524 
       
   525     $ echo "print 'Yeh Fevicol ka Majboot jod hai, tootega nahin'" > feviStick.py
       
   526     $ hg st
       
   527     M feviStick.py
       
   528 
       
   529 And commit the changes made ::
       
   530 
       
   531     $ hg ci -u "Shantanu <shantanu@fossee.in>" -m "Updated tag line for feviCol.py."
       
   532     $ hg st
       
   533     $ hg tip
       
   534     changeset:   4:caf986b15e05
       
   535     tag:         tip
       
   536     user:        Shantanu <shantanu@fossee.in>
       
   537     date:        Tue Aug 25 16:28:24 2009 +0530
       
   538     summary:     Updated tag line for feviCol.py.
       
   539 
       
   540 Now we will make some changes on Fevicol repo. We will add new file here ::
       
   541 
       
   542     $ cd Fevicol
       
   543     $ echo "print 'Jor laga ke hayyiya'" > firstAdd.py
       
   544     $ hg st
       
   545     ? firstAdd.py
       
   546     $ hg add firstAdd.py
       
   547     $ hg st
       
   548     A firstAdd.py
       
   549     $ hg ci -u "Shantanu <shantanu@fossee.in>" -m "Added firsAdd.py."
       
   550     $ hg tip
       
   551     changeset:   4:fadbd6492cc4
       
   552     tag:         tip
       
   553     user:        Shantanu <shantanu@fossee.in>
       
   554     date:        Tue Aug 25 16:46:24 2009 +0530
       
   555     summary:     Added firsAdd.py.
       
   556     
       
   557 So now we have two repo, who have different commit history and tree, now if we try to pull changes from one to another, this is how it goes(we are still in Fevicol repo): ::
       
   558 
       
   559     $ hg pull ../Fevicol-clone 
       
   560     pulling from ../Fevicol-clone
       
   561     searching for changes
       
   562     adding changesets
       
   563     adding manifests
       
   564     adding file changes
       
   565     added 1 changesets with 1 changes to 1 files (+1 heads)
       
   566     (run 'hg heads' to see heads, 'hg merge' to merge)
       
   567 
       
   568 There we go, since both repo were on different track, hg pull command in last line gives some heading from here. *hg heads* command show current repository heads or show branch heads. ::
       
   569 
       
   570     $ hg heads
       
   571     changeset:   5:caf986b15e05
       
   572     tag:         tip
       
   573     parent:      3:e1ab2aff4ddd
       
   574     user:        Shantanu <shantanu@fossee.in>
       
   575     date:        Tue Aug 25 16:28:24 2009 +0530
       
   576     summary:     Updated tag line for feviCol.py.
       
   577 
       
   578     changeset:   4:fadbd6492cc4
       
   579     user:        Shantanu <shantanu@fossee.in>
       
   580     date:        Tue Aug 25 16:46:24 2009 +0530
       
   581     summary:     Added firsAdd.py.
       
   582     
       
   583 To get better understanding of what is going on hg have a tool known as *glog* which shows revision history alongside an ASCII revision graph. ::
       
   584      
       
   585     $ hg glog
       
   586     o  changeset:   5:caf986b15e05
       
   587     |  tag:         tip
       
   588     |  parent:      3:e1ab2aff4ddd
       
   589     |  user:        Shantanu <shantanu@fossee.in>
       
   590     |  date:        Tue Aug 25 16:28:24 2009 +0530
       
   591     |  summary:     Updated tag line for feviCol.py.
       
   592     |
       
   593     | @  changeset:   4:fadbd6492cc4
       
   594     |/   user:        Shantanu <shantanu@fossee.in>
       
   595     |    date:        Tue Aug 25 16:46:24 2009 +0530
       
   596     |    summary:     Added firsAdd.py.
       
   597     |
       
   598     o  changeset:   3:e1ab2aff4ddd
       
   599     |  user:        Shantanu Choudhary <shantanu@fossee.in>
       
   600     |  date:        Sun Aug 23 23:32:01 2009 +0530
       
   601     |  summary:     Changed tagline for feviStick.py.
       
   602     |
       
   603     o  changeset:   2:a7912d45f47c
       
   604     |  user:        Shantanu <shantanu@fossee.in>
       
   605     |  date:        Sun Aug 23 22:34:35 2009 +0530
       
   606     |  summary:     Updated Content.
       
   607     |
       
   608     o  changeset:   1:d948fb4137c5
       
   609     |  user:        Shantanu <shantanu@fossee.in>
       
   610     |  date:        Sat Aug 22 00:11:25 2009 +0530
       
   611     |  summary:     Renamed pidiLite.py.
       
   612     |
       
   613     o  changeset:   0:84f5e91f4de1
       
   614        user:        Shantanu <shantanu@fossee.in>
       
   615        date:        Fri Aug 21 23:37:13 2009 +0530
       
   616        summary:     First commit.
       
   617 
       
   618 To bring repo on single track/branch once again we will have to merge these two branches. Without merging them even hg update wont work for obvious reason of confusing track record. ::
       
   619 
       
   620     $ hg up
       
   621     abort: crosses branches (use 'hg merge' or 'hg update -C')
       
   622 
       
   623 *hg merge* command merge working directory with another revision. ::
       
   624 
       
   625     $ hg merge
       
   626     1 files updated, 0 files merged, 0 files removed, 0 files unresolved
       
   627     (branch merge, don't forget to commit) 
       
   628     $ hg tip 
       
   629     changeset:   5:caf986b15e05
       
   630     tag:         tip
       
   631     parent:      3:e1ab2aff4ddd
       
   632     user:        Shantanu <shantanu@fossee.in>
       
   633     date:        Tue Aug 25 16:28:24 2009 +0530
       
   634     summary:     Updated tag line for feviCol.py.
       
   635 
       
   636 After merging two branches, until we commit the results of merge it will keep on showing two heads. ::
       
   637 
       
   638     $ hg ci -u "Shantanu <shantanu@fossee.in>" -m "Merged branches of add and tag line."
       
   639     $ hg heads 
       
   640     changeset:   6:edbe97209954
       
   641     tag:         tip
       
   642     parent:      4:fadbd6492cc4
       
   643     parent:      5:caf986b15e05
       
   644     user:        Shantanu <shantanu@fossee.in>
       
   645     date:        Tue Aug 25 17:06:03 2009 +0530
       
   646     summary:     Merged branches of add and tag line.
       
   647 
       
   648 Here is brief and meaningful output of glog ::
       
   649 
       
   650     $ hg glog 
       
   651     @    changeset:   6:edbe97209954
       
   652     |\   tag:         tip
       
   653     | |  parent:      4:fadbd6492cc4
       
   654     | |  parent:      5:caf986b15e05
       
   655     | |  user:        Shantanu <shantanu@fossee.in>
       
   656     | |  date:        Tue Aug 25 17:06:03 2009 +0530
       
   657     | |  summary:     Merged branches of add and tag line.
       
   658     | |
       
   659     | o  changeset:   5:caf986b15e05
       
   660     | |  parent:      3:e1ab2aff4ddd
       
   661     | |  user:        Shantanu <shantanu@fossee.in>
       
   662     | |  date:        Tue Aug 25 16:28:24 2009 +0530
       
   663     | |  summary:     Updated tag line for feviCol.py.
       
   664     | |
       
   665     o |  changeset:   4:fadbd6492cc4
       
   666     |/   user:        Shantanu <shantanu@fossee.in>
       
   667     |    date:        Tue Aug 25 16:46:24 2009 +0530
       
   668     |    summary:     Added firsAdd.py.
       
   669 
       
   670 And we are back on track.
       
   671 
       
   672 Workflow:
       
   673 =========
       
   674 
       
   675 This is chain of steps which can be followed for working against a project that has a centralized copy, you may want to make sure you're up to date first. This means pulling its changes and then updating. 
       
   676 
       
   677 For example: ::
       
   678     
       
   679     $ hg pull
       
   680     $ hg update
       
   681 
       
   682 This will grab the remote changes from the location you first cloned from. Then it will apply the changes. You can do this in one go with: ::
       
   683 
       
   684     $ hg pull -u
       
   685 
       
   686 Now let's say you make some changes. You edit a file and you want to commit your change. You can do this with: ::
       
   687 
       
   688     $ hg commit
       
   689 
       
   690 An editor will pop-up asking you to write a message describing your change. When you're done for the day, and you have required changesets sitting in your repository. Before pushing to upstream make sure to pull and update and merge branches if required, once everything looks okay and you have single track, push the changes, ::
       
   691 
       
   692     $ hg push
       
   693 
       
   694 Suggested Reading:
       
   695 ==================
       
   696 
       
   697 	* http://karlagius.com/2009/01/09/version-control-for-the-masses/
       
   698 	* http://betterexplained.com/articles/a-visual-guide-to-version-control/
       
   699 	* http://en.wikipedia.org/wiki/Revision_control
       
   700 	* http://hgbook.red-bean.com/
       
   701 	* http://betterexplained.com/articles/intro-to-distributed-version-control-illustrated/
       
   702 	* http://wiki.alliedmods.net/Mercurial_Tutorial