Advanced Bash−Scripting Guide

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[[ condition1 && condition2 ]] Advanced Bash−Scripting Guide The −o and −a operators work with the test command or occur within single test brackets. if [ "$exp1" −a "$exp2" ] Refer to Example 8−3 and Example 26−10 to see compound comparison operators in action. 7.4. Nested if/then Condition Tests Condition tests using the if/then construct may be nested. The net result is identical to using the && compound comparison operator above. if [ condition1 ] then if [ condition2 ] then do−something # But only if both "condition1" and "condition2" valid. fi fi See Example 35−4 for an example of nested if/then condition tests. 7.5. Testing Your Knowledge of Tests The systemwide xinitrc file can be used to launch the X server. This file contains quite a number of if/then tests, as the following excerpt shows. if [ −f $HOME/.Xclients ]; then exec $HOME/.Xclients elif [ −f /etc/X11/xinit/Xclients ]; then exec /etc/X11/xinit/Xclients else # failsafe settings. Although we should never get here # (we provide fallbacks in Xclients as well) it can't hurt. xclock −geometry 100x100−5+5 & xterm −geometry 80x50−50+150 & if [ −f /usr/bin/netscape −a −f /usr/share/doc/HTML/index.html ]; then netscape /usr/share/doc/HTML/index.html & fi fi Explain the "test" constructs in the above excerpt, then examine the entire file, /etc/X11/xinit/xinitrc, and analyze the if/then test constructs there. You may need to refer ahead to the discussions of grep, sed, and regular expressions. Chapter 7. Tests 54
Chapter 8. Operations and Related Topics 8.1. Operators assignment variable assignment Initializing or changing the value of a variable = All−purpose assignment operator, which works for both arithmetic and string assignments. var=27 category=minerals # No spaces allowed after the "=". Do not confuse the "=" assignment operator with the = test operator. # = as a test operator if [ "$string1" = "$string2" ] # if [ "X$string1" = "X$string2" ] is safer, # to prevent an error message should one of the variables be empty. # (The prepended "X" characters cancel out.) then command fi arithmetic operators + − * / ** plus minus multiplication division exponentiation # Bash, version 2.02, introduced the "**" exponentiation operator. % let "z=5**3" echo "z = $z" # z = 125 modulo, or mod (returns the remainder of an integer division operation) bash$ echo `expr 5 % 3` 2 This operator finds use in, among other things, generating numbers within a specific range (see Example 9−23 and Example 9−25) and formatting program output (see Example 26−9 and Example Chapter 8. Operations and Related Topics 55
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Chapter 1. Why Shell Programming? A
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As is the case with for/in loops, p
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This construct tests for a conditio
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# Accept upper or lowercase input.
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# May need to also press ENTER if a
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cat, tac # Burn the CDR. cdrecord
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Advanced Bash−Scripting Guide 12.
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exit $E_CHANGED_MIND ;; *) echo "De
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The multiplication operator must be
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echo Number of digits at the beginn
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Outputs very verbose timing statist
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This line occurs three times. This
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# List all the users in /etc/passwd
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Advanced Bash−Scripting Guide # r
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Advanced Bash−Scripting Guide gre
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The −d option deletes a range of
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# Delete CR and write to new file.
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mailto Similar to the mail command,
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[ ${NETWORKING} = "no" ] && exit 0
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chroot Advanced Bash−Scripting Gu
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Chapter 15. Arithmetic Expansion Ar
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# Saves stdin. Advanced Bash−Scri
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Chapter 17. Here Documents A here d
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Example 17−11. A self−documenti
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Part 4. Advanced Topics At this poi
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"Sed & Awk", by Dougherty and Robbi
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Chapter 20. Subshells Running a she
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# Range: 0 − 200 # It's crude, bu
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# grep PATTERN /etc/passwd | awk
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Advanced Bash−Scripting Guide # Y
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Chapter 25. List Constructs The "an
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# AND LIST executes on true, OR LIS
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echo ${colors[$index]} let "index =
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# Replace all matching wildcarded s
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fi let "t += $i " Primes[t]=$NON_PR
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# −−−−−−−−− # 1)
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Chapter 28. /dev and /proc A Linux
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Chapter 30. Debugging The Bash shel
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4. Advanced Bash−Scripting Guide
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Chapter 31. Options Options are set
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Chapter 32. Gotchas Turandot: Gli e
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command1 2> − | command2 # Trying
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echo "one two three" | read a b c #
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Chapter 33. Scripting With Style Ge
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#!/bin/bash # color−echo.sh: Echo
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34.7. Assorted Tips Advanced Bash
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# agram.sh: Playing games with anag
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Chapter 35. Bash, version 2 The cur
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1−56592−580−7). This is the s
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Bibliography Edited by Peter Dennin
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Mark Komarinski's Printing−Usage
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let "row = $r" # Count center row o
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next_gen "$Cur" let "generation +=
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[−c localdirectory] [−m filepat
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Advanced Bash−Scripting Guide #:d
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# ListDirectory "FileGlob" "Field
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Advanced Bash−Scripting Guide # I
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The md5sum program is documented as
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Note: 'mount −l' does return the
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Advanced Bash−Scripting Guide dec
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Appendix B. A Sed and Awk Micro−P
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Appendix D. A Detailed Introduction
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Appendix E. Localization Localizati
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Appendix F. History Commands The Ba
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Appendix H. Converting DOS Batch Fi
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Appendix I. Exercises I.1. Analyzin
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Lottery Numbers One type of lottery
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[33] This is actually a script adap
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# Thanks to Stephane Chazelas for p
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