Bash-Beginners-Guide

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Bash Guide for Beginners do count=$(( $count + 1 )) done # # Now we calculate whose turn it is. # week=`date '+%W'` # The week of the year (0..53). week=${week#0} # Remove possible leading zero. let "index = $week % $count" email=${wholist[index]} # week modulo count = the lucky person # Get the lucky person's e-mail address. echo $email # Output the person's e-mail address. This script is then used in other scripts, such as this one, which uses a here document: email=`get-tester-address.sh` hostname=`hostname` # Find who to e-mail. # This machine's name. # # Send e-mail to the right person. # mail $email -s '[Demo Testing]'
10.3.3. Transformations of variables Bash Guide for Beginners 10.3.3.1. Substitution ${VAR:-WORD} If VAR is not defined or null, the expansion of WORD is substituted; otherwise the value of VAR is substituted: [bob in ~] echo ${TEST:-test} test [bob in ~] echo $TEST [bob in ~] export TEST=a_string [bob in ~] echo ${TEST:-test} a_string [bob in ~] echo ${TEST2:-$TEST} a_string This form is often used in conditional tests, for instance in this one: [ -z "${COLUMNS:-}" ] && COLUMNS=80 It is a shorter notation for if [ -z "${COLUMNS:-}" ]; then COLUMNS=80 fi See Section 7.1.2.3 for more information about this type of condition testing. If the hyphen (-) is replaced with the equal sign (=), the value is assigned to the parameter if it does not exist: [bob in ~] echo $TEST2 [bob in ~] echo ${TEST2:=$TEST} a_string [bob in ~] echo $TEST2 a_string The following syntax tests the existence of a variable. If it is not set, the expansion of WORD is printed to standard out and non-interactive shells quit. A demonstration: [bob in ~] cat vartest.sh #!/bin/bash # This script tests whether a variable is set. If not, # it exits printing a message. echo ${TESTVAR:?"There's so much I still wanted to do..."} echo "TESTVAR is set, we can proceed." [bob in testdir] ./vartest.sh ./vartest.sh: line 6: TESTVAR: There's so much I still wanted to do... Chapter 10. More on variables 127
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Bash Guide for Beginners Machtelt G
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Bash Guide for Beginners Table of C
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Bash Guide for Beginners Table of C
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Table of Contents Glossary C.......
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Introduction 1. Why this guide? The
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Revision 1.6 2005-03-01 Revised by:
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Bash Guide for Beginners See Chapte
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Bash Guide for Beginners mia:~> cat
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Bash Guide for Beginners When invok
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More information about the file des
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Built-in commands are necessary to
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• Brace expansion • Tilde expan
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A number of methods can be used; on
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Bash Guide for Beginners stop in ea
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Chapter 2. Writing and debugging sc
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the documentation of your favorite
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Bash Guide for Beginners Comments a
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Bash Guide for Beginners + set +x I
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Chapter 3. The Bash environment In
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Bash Guide for Beginners local pid
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MOZILLA_FIVE_HOME=/usr/lib/mozilla
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Bash Guide for Beginners franky ~>
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the GNU Awk programming language is
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Bash Guide for Beginners 3.2.4. Res
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LINES MACHTYPE MAILCHECK OLDPWD OPT
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two is the second positional parame
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Bash Guide for Beginners 3.3.1. Why
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A correctly-formed brace expansion
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Bash Guide for Beginners If the sub
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of the whitespace characters "space
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Bash Guide for Beginners /dev/hda5
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Bash Guide for Beginners 3.7. Summa
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Two regular expressions may be conc
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LABEL=/ / ext3 defaults 1 1 If this
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cathy ~> ls -ld [[:digit:]]* drwxrw
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Bash Guide for Beginners p Print te
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sandy ~> sed -n '/a text/,/This/p'
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Bash Guide for Beginners # This is
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Chapter 6. The GNU awk programming
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Bash Guide for Beginners 121script.
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Bash Guide for Beginners amd.conf a
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Page 123 and 124: ;; 2) $FORTUNE startrek ;; 3) $FORT
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Page 159 and 160: Send and receive mail. man Read man
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Page 165 and 166: Index A aliases Section 3.5.1 ANSI-
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Page 171 and 172: eadonly Section 10.1.3 regular expr
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