mirror of https://github.com/tLDP/LDP
65 lines
1.8 KiB
Bash
65 lines
1.8 KiB
Bash
#! /bin/bash
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# array-assign.bash
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# Array operations are Bash specific,
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#+ hence the ".bash" in the script name.
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# Copyright (c) Michael S. Zick, 2003, All rights reserved.
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# License: Unrestricted reuse in any form, for any purpose.
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# Version: $ID$
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# Based on an example provided by Stephane Chazelas
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#+ which appeared in the book: Advanced Bash Scripting Guide.
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# Output format of the 'times' command:
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# User CPU <space> System CPU
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# User CPU of dead children <space> System CPU of dead children
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# Bash has two versions of assigning all elements of an array
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#+ to a new array variable.
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# Both drop 'null reference' elements
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#+ in Bash versions 2.04, 2.05a and 2.05b.
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# An additional array assignment that maintains the relationship of
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#+ [subscript]=value for arrays may be added to newer versions.
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# Constructs a large array using an internal command,
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#+ but anything creating an array of several thousand elements
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#+ will do just fine.
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declare -a bigOne=( /dev/* )
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echo
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echo 'Conditions: Unquoted, default IFS, All-Elements-Of'
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echo "Number of elements in array is ${#bigOne[@]}"
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# set -vx
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echo
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echo '- - testing: =( ${array[@]} ) - -'
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times
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declare -a bigTwo=( ${bigOne[@]} )
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# ^ ^
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times
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echo
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echo '- - testing: =${array[@]} - -'
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times
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declare -a bigThree=${bigOne[@]}
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# No parentheses this time.
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times
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# Comparing the numbers shows that the second form, pointed out
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#+ by Stephane Chazelas, is from three to four times faster.
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# I will continue to use the first form in my example descriptions
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#+ because I think it is a better illustration of what is happening.
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# The reusable portions of my examples will actual contain
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#+ the second form where appropriate because of the speedup.
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# MSZ: Sorry about that earlier oversight folks.
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exit 0
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