| changeset 60 | 8a36825e21c5 |
| parent 59 | 8c15077f028d |
| child 63 | dc13f22e9489 |
| 59:8c15077f028d | 60:8a36825e21c5 |
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9 * What are Shell Scripts U |
9 * What are Shell Scripts U |
10 - Able to use file comparison commands like Ap |
10 - Able to use file comparison commands like Ap |
11 diff, cmp, comm |
11 diff, cmp, comm |
12 - Create and extract archives(.tar files) and zipped files(.gz) Ap |
12 - Create and extract archives(.tar files) and zipped files(.gz) Ap |
13 - Set/Modify environment as per need Ap |
13 - Set/Modify environment as per need Ap |
14 - Create shell scripts to autmoate tasks. Ap |
14 - Create shell scripts to automate tasks. Ap |
15 |
15 |
16 tar: |
16 tar: |
17 ==== |
17 ==== |
18 |
18 |
19 Introduction: |
19 Introduction: |
429 These spaces in between operator and operands is important, without them shell interpreter will raise the syntax error. :: |
429 These spaces in between operator and operands is important, without them shell interpreter will raise the syntax error. :: |
430 |
430 |
431 $ expr 2*3 |
431 $ expr 2*3 |
432 expr: syntax error |
432 expr: syntax error |
433 |
433 |
434 One can use backquotes(`) also to get value of expr. :: |
434 One can use back-quotes(`) also to get value of expr. :: |
435 |
435 |
436 $ echo `expr 6 + 3` |
436 $ echo `expr 6 + 3` |
437 9 |
437 9 |
438 $ result=`expr 6 + 3` |
438 $ result=`expr 6 + 3` |
439 $ echo $result |
439 $ echo $result |
440 9 |
440 9 |
441 |
441 |
442 Shell uses three kinds of quotes. Double quotes("), anything enclosed among them except from variable trailing after $, and characters after \ would be printed as it is. Single quotes('), anything enclsed within them is just same, no formulation/interpretaion. Back quotes(`), anything inclosed is considered as command, or is executed. :: |
442 Shell uses three kinds of quotes. Double quotes("), anything enclosed among them except from variable trailing after $, and characters after \ would be printed as it is. Single quotes('), anything enclosed within them is just same, no formulation/interpretation. Back quotes(`), anything inclosed is considered as command, or is executed. :: |
443 |
443 |
444 $ echo "Today is date" |
444 $ echo "Today is date" |
445 Today is date |
445 Today is date |
446 $ echo "Today is `date`" |
446 $ echo "Today is `date`" |
447 Today is Wed Sep 16 17:32:22 IST 2009 |
447 Today is Wed Sep 16 17:32:22 IST 2009 |
451 Today is \n Wed Sep 16 17:40:13 IST 2009 |
451 Today is \n Wed Sep 16 17:40:13 IST 2009 |
452 $ echo -e "Today is \n `date`" |
452 $ echo -e "Today is \n `date`" |
453 Today is |
453 Today is |
454 Wed Sep 16 17:41:13 IST 2009 |
454 Wed Sep 16 17:41:13 IST 2009 |
455 |
455 |
456 if construct: |
456 if else construct: |
457 ------------- |
457 ------------------ |
458 |
458 |
459 One can have simple *if else if* constructs in shell scripts to check conditions. Lets take simple example of writing a script which returns back whether the argument passed is positive or not: :: |
459 One can have simple *if else if* constructs in shell scripts to check conditions. Lets take simple example of writing a script which returns back whether the argument passed is positive or not: :: |
460 |
460 |
461 #!/bin/sh |
461 #!/bin/sh |
462 if test $1 -gt 0 |
462 if test $1 -gt 0 |
592 read variable |
592 read variable |
593 echo "Input - $variable" |
593 echo "Input - $variable" |
594 done |
594 done |
595 exit 0 |
595 exit 0 |
596 |
596 |
597 Now lets try and use these above mentioned options provided by shell to write a utility. Until now, when we try find or locate it looks through directories and files for result. But they wont search through tar archives and zipped files. Lets create a shell script for especially looking through these files: :: |
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598 |
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599 #!/bin/sh |
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600 |
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601 #To check number of arguments being passed. |
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602 if [ $# -eq 0 ] ; then |
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603 echo "Correct usage: $0 tar-archive filename \nOr $0 filename" |
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604 exit 1 |
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605 else |
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606 if [ $# -eq 1 ] ; then |
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607 tar_archive=`find $PWD -name "*.tar*"` |
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608 else |
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609 tar_archive=`find $PWD -name $1` |
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610 fi |
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611 fi |
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612 |
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613 #Search of particular file inside archives. |
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614 for archive in $tar_archive |
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615 do |
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616 echo $archive |
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617 variable=`tar -tf $archive` |
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618 for word in $variable |
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619 do |
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620 if [ $# -eq 1 ] ; then |
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621 echo "$word" | grep -q ".*$1" |
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622 else |
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623 echo "$word" | grep -q ".*$2" |
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624 fi |
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625 if [ $? -eq 0 ] ; then |
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626 echo "File present in $archive!" |
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627 fi |
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628 done |
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629 done |
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630 |
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597 ``until`` |
631 ``until`` |
598 ~~~~~~~~~ |
632 ~~~~~~~~~ |
599 |
633 |
600 The ``until`` loop is similar to the ``while`` loop, except that it executes until the conditional command does not execute properly. |
634 The ``until`` loop is similar to the ``while`` loop, except that it executes until the conditional command does not execute properly. |
601 |
635 |
659 |
693 |
660 |
694 |
661 Further Reading: |
695 Further Reading: |
662 ---------------- |
696 ---------------- |
663 * http://www.freeos.com/guides/lsst/ |
697 * http://www.freeos.com/guides/lsst/ |
664 * http://www.freeos.com/guides/lsst/ch02sec01.html |
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665 * http://bash.cyberciti.biz/guide/Main_Page |
698 * http://bash.cyberciti.biz/guide/Main_Page |
699 * http://tldp.org/LDP/abs/html/ |
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700 * http://tldp.org/LDP/Bash-Beginners-Guide/html/Bash-Beginners-Guide.html |
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666 |
701 |
702 |
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703 .. LocalWords: allfiles txt cvf vf tf regex mkdir cp cd xvf gzip gz stdout |