Advanced Bash−Scripting Guide

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Advanced Bash−Scripting Guide bash$ echo 2222 | gawk −−re−interval '/2{3}/' 2222 Perl and some egrep versions do not require escaping the curly brackets. • Parentheses −− ( ) −− enclose groups of REs. They are useful with the following "|" operator and in substring extraction using expr. • The −− | −− "or" RE operator matches any of a set of alternate characters. bash$ egrep 're(a|e)d' misc.txt People who read seem to be better informed than those who do not. The clarinet produces sound by the vibration of its reed. Some versions of sed, ed, and ex support escaped versions of the extended regular expressions described above. • POSIX Character Classes. [:class:] This is an alternate method of specifying a range of characters to match. • [:alnum:] matches alphabetic or numeric characters. This is equivalent to [A−Za−z0−9]. • [:alpha:] matches alphabetic characters. This is equivalent to [A−Za−z]. • [:blank:] matches a space or a tab. • [:cntrl:] matches control characters. • [:digit:] matches (decimal) digits. This is equivalent to [0−9]. • [:graph:] (graphic printable characters). Matches characters in the range of ASCII 33 − 126. This is the same as [:print:], below, but excluding the space character. • [:lower:] matches lowercase alphabetic characters. This is equivalent to [a−z]. • [:print:] (printable characters). Matches characters in the range of ASCII 32 − 126. This is the same as [:graph:], above, but adding the space character. • [:space:] matches whitespace characters (space and horizontal tab). • [:upper:] matches uppercase alphabetic characters. This is equivalent to [A−Z]. • [:xdigit:] matches hexadecimal digits. This is equivalent to [0−9A−Fa−f]. POSIX character classes generally require quoting or double brackets ([[ ]]). bash$ grep [[:digit:]] test.file abc=723 These character classes may even be used with globbing, to a limited extent. bash$ ls −l ?[[:digit:]][[:digit:]]? −rw−rw−r−− 1 bozo bozo 0 Aug 21 14:47 a33b To see POSIX character classes used in scripts, refer to Example 12−14 and Example 12−15. Sed, awk, and Perl, used as filters in scripts, take REs as arguments when "sifting" or transforming files or I/O streams. See Example A−13 and Example A−18 for illustrations of this. Chapter 19. Regular Expressions 264
"Sed & Awk", by Dougherty and Robbins gives a very complete and lucid treatment of REs (see the Bibliography). 19.2. Globbing Advanced Bash−Scripting Guide Bash itself cannot recognize Regular Expressions. In scripts, commands and utilities, such as sed and awk, interpret RE's. Bash does carry out filename expansion, a process known as "globbing", but this does not use the standard RE set. Instead, globbing recognizes and expands wildcards. Globbing interprets the standard wildcard characters, * and ?, character lists in square brackets, and certain other special characters (such as ^ for negating the sense of a match). There are some important limitations on wildcard characters in globbing, however. Strings containing * will not match filenames that start with a dot, as, for example, .bashrc. [49] Likewise, the ? has a different meaning in globbing than as part of an RE. bash$ ls −l total 2 −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 a.1 −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 b.1 −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 c.1 −rw−rw−r−− 1 bozo bozo 466 Aug 6 17:48 t2.sh −rw−rw−r−− 1 bozo bozo 758 Jul 30 09:02 test1.txt bash$ ls −l t?.sh −rw−rw−r−− 1 bozo bozo 466 Aug 6 17:48 t2.sh bash$ ls −l [ab]* −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 a.1 −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 b.1 bash$ ls −l [a−c]* −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 a.1 −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 b.1 −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 c.1 bash$ ls −l [^ab]* −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 c.1 −rw−rw−r−− 1 bozo bozo 466 Aug 6 17:48 t2.sh −rw−rw−r−− 1 bozo bozo 758 Jul 30 09:02 test1.txt bash$ ls −l {b*,c*,*est*} −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 b.1 −rw−rw−r−− 1 bozo bozo 0 Aug 6 18:42 c.1 −rw−rw−r−− 1 bozo bozo 758 Jul 30 09:02 test1.txt bash$ echo * a.1 b.1 c.1 t2.sh test1.txt bash$ echo t* t2.sh test1.txt Even an echo command performs wildcard expansion on filenames. See also Example 10−4. Chapter 19. Regular Expressions 265
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Chapter 1. Why Shell Programming? A
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Chapter 2. Starting Off With a Sha
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Chapter 3. Special Characters Speci
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# Sometimes, though, you get: # 11
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The "−" can be used to pipe stdou
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change the behavior of the terminal
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Chapter 4. Introduction to Variable
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The shift command reassigns the pos
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Example 5−1. Echoing Weird Variab
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(cd /source/directory && tar cf −
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true # the "true" builtin. echo "ex
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if [[ −e $file ]] then echo "Pass
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7.3. Comparison operators (binary)
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Example 7−5. arithmetic and strin
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Chapter 8. Operations and Related T
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Part 3. Beyond the Basics Table of
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$EDITOR the default editor invoked
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Example 9−2. Timed Input Advanced
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echo 'IFS=":", using "$@"' c=0 for
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echo '${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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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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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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# ListDirectory "FileGlob" "Field
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The md5sum program is documented as
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Note: 'mount −l' does return the
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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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