Advanced Bash−Scripting Guide

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Advanced Bash−Scripting Guide #+ declared and set within the function. } original_array=( element1 element2 element3 element4 element5 ) echo echo "original_array = ${original_array[@]}" # List all elements of original array. # This is the trick that permits passing an array to a function. # ********************************** argument=`echo ${original_array[@]}` # ********************************** # Pack a variable #+ with all the space−separated elements of the original array. # # Note that attempting to just pass the array itself will not work. # This is the trick that allows grabbing an array as a "return value". # ***************************************** returned_array=( `Pass_Array "$argument"` ) # ***************************************** # Assign 'echoed' output of function to array variable. echo "returned_array = ${returned_array[@]}" echo "=============================================================" # Now, try it again, #+ attempting to access (list) the array from outside the function. Pass_Array "$argument" # The function itself lists the array, but... #+ accessing the array from outside the function is forbidden. echo "Passed array (within function) = ${passed_array[@]}" # NULL VALUE since this is a variable local to the function. echo exit 0 For a more elaborate example of passing arrays to functions, see Example A−11. • Using the double parentheses construct, it is possible to use C−like syntax for setting and incrementing variables and in for and while loops. See Example 10−12 and Example 10−17. • A useful scripting technique is to repeatedly feed the output of a filter (by piping) back to the same filter, but with a different set of arguments and/or options. Especially suitable for this are tr and grep. # From "wstrings.sh" example. wlist=`strings "$1" | tr A−Z a−z | tr '[:space:]' Z | \ tr −cs '[:alpha:]' Z | tr −s '\173−\377' Z | tr Z ' '` Example 34−13. Fun with anagrams #!/bin/bash Chapter 34. Miscellany 352
# agram.sh: Playing games with anagrams. # Find anagrams of... LETTERSET=etaoinshrdlu Advanced Bash−Scripting Guide anagram "$LETTERSET" | # Find all anagrams of the letterset... grep '.......' | # With at least 7 letters, grep '^is' | # starting with 'is' grep −v 's$' | # no plurals grep −v 'ed$' # no past tense verbs # Uses "anagram" utility #+ that is part of the author's "yawl" word list package. # http://ibiblio.org/pub/Linux/libs/yawl−0.2.tar.gz exit 0 # End of code. bash$ sh agram.sh islander isolate isolead isotheral See also Example 28−2, Example 12−18, and Example A−10. • Use "anonymous here documents" to comment out blocks of code, to save having to individually comment out each line with a #. See Example 17−10. • Running a script on a machine that relies on a command that might not be installed is dangerous. Use whatis to avoid potential problems with this. CMD=command1 PlanB=command2 # First choice. # Fallback option. command_test=$(whatis "$CMD" | grep 'nothing appropriate') # If 'command1' not found on system , 'whatis' will return #+ "command1: nothing appropriate." if [[ −z "$command_test" ]] # Check whether command present. then $CMD option1 option2 # Run command1 with options. else # Otherwise, $PlanB #+ run command2. fi • The run−parts command is handy for running a set of command scripts in sequence, particularly in combination with cron or at. • It would be nice to be able to invoke X−Windows widgets from a shell script. There happen to exist several packages that purport to do so, namely Xscript, Xmenu, and widtools. The first two of these no longer seem to be maintained. Fortunately, it is still possible to obtain widtools here. The widtools (widget tools) package requires the XForms library to be installed. Additionally, the Makefile needs some judicious editing before the package will build on a typical Linux system. Finally, three of the six widgets offered do not work (and, in fact, segfault). For more effective scripting with widgets, try Tk or wish (Tcl derivatives), PerlTk (Perl with Tk extensions), tksh (ksh with Tk extensions), XForms4Perl (Perl with XForms extensions), Gtk−Perl (Perl with Gtk extensions), or PyQt (Python with Qt extensions). Chapter 34. Miscellany 353
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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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[ ${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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Page 389 and 390: let "row = $r" # Count center row o
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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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