Advanced Bash−Scripting Guide

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(( 5 − 5 )) # 0 echo "Exit status of \"(( 5 − 5 ))\" is $?." # 1 (( 5 / 4 )) # Division o.k. echo "Exit status of \"(( 5 / 4 ))\" is $?." # 0 (( 1 / 2 )) # Division result < 1. echo "Exit status of \"(( 1 / 2 ))\" is $?." # Rounded off to 0. # 1 (( 1 / 0 )) 2>/dev/null # Illegal division by 0. echo "Exit status of \"(( 1 / 0 ))\" is $?." # 1 # What effect does the "2>/dev/null" have? # What would happen if it were removed? # Try removing it, then rerunning the script. exit 0 7.2. File test operators Returns true if... Advanced Bash−Scripting Guide −e −f −s −d −b −c −p −h −L −S −t −r −w −x file exists file is a regular file (not a directory or device file) file is not zero size file is a directory file is a block device (floppy, cdrom, etc.) file is a character device (keyboard, modem, sound card, etc.) file is a pipe file is a symbolic link file is a symbolic link file is a socket file (descriptor) is associated with a terminal device This test option may be used to check whether the stdin ([ −t 0 ]) or stdout ([ −t 1 ]) in a given script is a terminal. file has read permission (for the user running the test) file has write permission (for the user running the test) Chapter 7. Tests 46
Advanced Bash−Scripting Guide −g −u file has execute permission (for the user running the test) set−group−id (sgid) flag set on file or directory If a directory has the sgid flag set, then a file created within that directory belongs to the group that owns the directory, not necessarily to the group of the user who created the file. This may be useful for a directory shared by a workgroup. set−user−id (suid) flag set on file A binary owned by root with set−user−id flag set runs with root privileges, even when an ordinary user invokes it. [16] This is useful for executables (such as pppd and cdrecord) that need to access system hardware. Lacking the suid flag, these binaries could not be invoked by a non−root user. −rwsr−xr−t 1 root 178236 Oct 2 2000 /usr/sbin/pppd −k A file with the suid flag set shows an s in its permissions. sticky bit set Commonly known as the "sticky bit", the save−text−mode flag is a special type of file permission. If a file has this flag set, that file will be kept in cache memory, for quicker access. [17] If set on a directory, it restricts write permission. Setting the sticky bit adds a t to the permissions on the file or directory listing. drwxrwxrwt 7 root 1024 May 19 21:26 tmp/ If a user does not own a directory that has the sticky bit set, but has write permission in that directory, he can only delete files in it that he owns. This keeps users from inadvertently overwriting or deleting each other's files in a publicly accessible directory, such as /tmp. −O you are owner of file −G group−id of file same as yours −N file modified since it was last read f1 −nt f2 file f1 is newer than f2 f1 −ot f2 file f1 is older than f2 f1 −ef f2 files f1 and f2 are hard links to the same file ! "not" −− reverses the sense of the tests above (returns true if condition absent). Example 7−4. Testing for broken links Chapter 7. Tests 47
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Page 37 and 38: The shift command reassigns the pos
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Chapter 10. Loops and Branches Oper
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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 #!/
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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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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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Advanced Bash−Scripting Guide ' c
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Advanced Bash−Scripting Guide Not
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Chapter 15. Arithmetic Expansion Ar
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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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Advanced Bash−Scripting Guide alt
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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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Advanced Bash−Scripting Guide whi
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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 See
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Advanced Bash−Scripting Guide tpu
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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 /GU
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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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Advanced Bash−Scripting Guide } X
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Advanced Bash−Scripting Guide *)
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Appendix H. Converting DOS Batch Fi
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Advanced Bash−Scripting Guide XCO
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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 Usi
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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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