Advanced Bash−Scripting Guide

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Revision 1.7 05 January 2003 Revised by: mc 'COCONUT' release: a couple of bugfixes, more material, one more script. Revision 1.8 10 May 2003 Revised by: mc 'BREADFRUIT' release: a number of bugfixes, more scripts and material. This tutorial assumes no previous knowledge of scripting or programming, but progresses rapidly toward an intermediate/advanced level of instruction . . . all the while sneaking in little snippets of UNIX wisdom and lore. It serves as a textbook, a manual for self−study, and a reference and source of knowledge on shell scripting techniques. The exercises and heavily−commented examples invite active reader participation, under the premise that the only way to really learn scripting is to write scripts. The latest update of this document, as an archived, bzip2−ed "tarball" including both the SGML source and rendered HTML, may be downloaded from the author's home site. See the change log for a revision history. Dedication For Anita, the source of all the magic
Advanced Bash−Scripting Guide Table of Contents Chapter 1. Why Shell Programming?...............................................................................................................1 Chapter 2. Starting Off With a Sha−Bang.......................................................................................................3 2.1. Invoking the script............................................................................................................................5 2.2. Preliminary Exercises.......................................................................................................................5 Part 2. Basics.......................................................................................................................................................6 Chapter 3. Special Characters...........................................................................................................................7 Chapter 4. Introduction to Variables and Parameters..................................................................................23 4.1. Variable Substitution......................................................................................................................23 4.2. Variable Assignment.......................................................................................................................25 4.3. Bash Variables Are Untyped..........................................................................................................26 4.4. Special Variable Types...................................................................................................................28 Chapter 5. Quoting...........................................................................................................................................32 Chapter 6. Exit and Exit Status.......................................................................................................................38 Chapter 7. Tests................................................................................................................................................40 7.1. Test Constructs...............................................................................................................................40 7.2. File test operators............................................................................................................................46 7.3. Comparison operators (binary).......................................................................................................49 7.4. Nested if/then Condition Tests.......................................................................................................54 7.5. Testing Your Knowledge of Tests..................................................................................................54 Chapter 8. Operations and Related Topics....................................................................................................55 8.1. Operators.........................................................................................................................................55 8.2. Numerical Constants.......................................................................................................................61 Part 3. Beyond the Basics.................................................................................................................................63 Chapter 9. Variables Revisited........................................................................................................................64 9.1. Internal Variables............................................................................................................................64 9.2. Manipulating Strings.......................................................................................................................79 9.2.1. Manipulating strings using awk............................................................................................83 9.2.2. Further Discussion.................................................................................................................84 9.3. Parameter Substitution....................................................................................................................84 9.4. Typing variables: declare or typeset...............................................................................................92 9.5. Indirect References to Variables.....................................................................................................94 9.6. $RANDOM: generate random integer............................................................................................96 9.7. The Double Parentheses Construct...............................................................................................101 Chapter 10. Loops and Branches..................................................................................................................103 10.1. Loops..........................................................................................................................................103 10.2. Nested Loops..............................................................................................................................113 10.3. Loop Control...............................................................................................................................114 i
Page 1: Advanced Bash−Scripting Guide An
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Page 7 and 8: Chapter 1. Why Shell Programming? A
Page 9 and 10: Chapter 2. Starting Off With a Sha
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Page 13 and 14: Chapter 3. Special Characters Speci
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Page 23 and 24: # Sometimes, though, you get: # 11
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Page 29 and 30: Chapter 4. Introduction to Variable
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Page 37 and 38: The shift command reassigns the pos
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Page 45 and 46: true # the "true" builtin. echo "ex
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Advanced Bash−Scripting Guide −
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7.3. Comparison operators (binary)
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Example 7−5. arithmetic and strin
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Chapter 8. Operations and Related T
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Advanced Bash−Scripting Guide let
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Part 3. Beyond the Basics Table of
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$EDITOR the default editor invoked
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Advanced Bash−Scripting Guide (Th
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Advanced Bash−Scripting Guide #!/
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Example 9−2. Timed Input Advanced
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Advanced Bash−Scripting Guide fi
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echo 'IFS=":", using "$@"' c=0 for
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Advanced Bash−Scripting Guide #+
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Advanced Bash−Scripting Guide use
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echo '${var1#$pattern1} =' "${var1#
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t=${path_name%/*.*} # Same effect a
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Chapter 10. Loops and Branches Oper
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Advanced Bash−Scripting Guide if
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Advanced Bash−Scripting Guide OUT
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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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Advanced Bash−Scripting Guide ###
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# Accept upper or lowercase input.
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Advanced Bash−Scripting Guide a=`
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# May need to also press ENTER if a
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Advanced Bash−Scripting Guide ret
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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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Advanced Bash−Scripting Guide Cop
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fi let "t += $i " Primes[t]=$NON_PR
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Advanced Bash−Scripting Guide # =
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# −−−−−−−−− # 1)
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Chapter 28. /dev and /proc A Linux
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Advanced Bash−Scripting Guide net
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Advanced Bash−Scripting Guide # A
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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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Advanced Bash−Scripting Guide # i
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#!/bin/bash # color−echo.sh: Echo
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34.7. Assorted Tips Advanced Bash
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Advanced Bash−Scripting Guide the
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Advanced Bash−Scripting Guide •
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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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Advanced Bash−Scripting Guide # R
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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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Advanced Bash−Scripting Guide * A
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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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Advanced Bash−Scripting Guide Tha
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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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Advanced Bash−Scripting Guide and
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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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