Advanced Bash−Scripting Guide

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Redirecting the output of the command to a file or even to /dev/null also takes care of this problem. suspend This has a similar effect to Control−Z, but it suspends the shell (the shell's parent process should resume it at an appropriate time). logout Exit a login shell, optionally specifying an exit status. times Gives statistics on the system time used in executing commands, in the following form: 0m0.020s 0m0.020s Advanced Bash−Scripting Guide kill This capability is of very limited value, since it is uncommon to profile and benchmark shell scripts. Forcibly terminate a process by sending it an appropriate terminate signal (see Example 13−4). Example 11−23. A script that kills itself #!/bin/bash # self−destruct.sh kill $$ # Script kills its own process here. # Recall that "$$" is the script's PID. echo "This line will not echo." # Instead, the shell sends a "Terminated" message to stdout. exit 0 # After this script terminates prematurely, #+ what exit status does it return? # # sh self−destruct.sh # echo $? # 143 # # 143 = 128 + 15 # TERM signal kill −l lists all the signals. A kill −9 is a "sure kill", which will usually terminate a process that stubbornly refuses to die with a plain kill. Sometimes, a kill −15 works. A "zombie process", that is, a process whose parent has terminated, cannot be killed (you can't kill something that is already dead), but init will usually clean it up sooner or later. command The command COMMAND directive disables aliases and functions for the command "COMMAND". builtin This is one of three shell directives that effect script command processing. The others are builtin and enable. Invoking builtin BUILTIN_COMMAND runs the command "BUILTIN_COMMAND" as a shell Chapter 11. Internal Commands and Builtins 146
Advanced Bash−Scripting Guide enable builtin, temporarily disabling both functions and external system commands with the same name. This either enables or disables a shell builtin command. As an example, enable −n kill disables the shell builtin kill, so that when Bash subsequently encounters kill, it invokes /bin/kill. The −a option to enable lists all the shell builtins, indicating whether or not they are enabled. The −f filename option lets enable load a builtin as a shared library (DLL) module from a properly compiled object file. [26]. autoload This is a port to Bash of the ksh autoloader. With autoload in place, a function with an "autoload" declaration will load from an external file at its first invocation. [27] This saves system resources. Note that autoload is not a part of the core Bash installation. It needs to be loaded in with enable −f (see above). Table 11−1. Job Identifiers Notation Meaning %N Job number [N] %S Invocation (command line) of job begins with string S %?S Invocation (command line) of job contains within it string S %% "current" job (last job stopped in foreground or started in background) %+ "current" job (last job stopped in foreground or started in background) %− Last job $! Last background process Chapter 11. Internal Commands and Builtins 147
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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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Page 155 and 156: cat, tac # Burn the CDR. cdrecord
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Page 159 and 160: exit $E_CHANGED_MIND ;; *) echo "De
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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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Advanced Bash−Scripting Guide # T
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# Saves stdin. Advanced Bash−Scri
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Advanced Bash−Scripting Guide 16.
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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 # 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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#!/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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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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[33] This is actually a script adap
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# Thanks to Stephane Chazelas for p
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