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copied!<h2>Little introduction</h2> <p>Tracking forks (like <code>$()</code>) as they consume lot more ressource than normal (sequential) execution, if you know which variable has to be modified in advance, you'll better to use <code>local</code> definition around your whole script and use function instead of having to make file access between commands:</p> <pre><code>#!/bin/bash # There is the `A` script local VAR function B() { read -a VAR </proc/uptime } B echo $VAR sleep 1 B echo $VAR </code></pre> <p>could output something like:</p> <pre><code>1610291.39 1610292.39 </code></pre> <p>with time to access <code>/bin/sleep</code> could be less than 1/100th of second.</p> <h3>A little demonstration:</h3> <pre><code>local V1 B1() { read -a V1 </proc/uptime } B1 ;echo $V1 ;for i in {0..10000} ;do B1 ;done ;echo $V1 1610843.78 1610844.38 printf "%d 1/100th of sec\n" $((161084438-161084378)) 60 1/100th of sec </code></pre> <p>I could set 10000x my variable in 60/100 seconds, while</p> <pre><code>B2() { local var read -a var </proc/uptime echo $var } V2=$(B2);echo $V2;for i in {0..10000};do V2=$(B2);done;echo $V2 1611121.33 1611168.01 printf "%d 1/100th of sec\n" $((161116801-161112133)) 4668 1/100th of sec </code></pre> <p>May take <strong>more</strong> time!</p> <p>If you really wanna keep all in separated file, as @alok suggested, you could <code>source</code> them, as this will not fork:</p> <pre><code>echo >/dev/shm/B3 'read -a V3 </proc/uptime' . /dev/shm/B3 ;echo $V3 ; for i in {0..10000};do . /dev/shm/B3;done;echo $V3 1612187.89 1612188.79 printf "%d 1/100th of sec\n" $((161218879-161218789)) 90 1/100th of sec </code></pre> <p>This is lot quicker than having to fork for each loop, but accessing to function via filesystem (even RAM pseudo filesystem, without access time) take some time.</p> <h2>My answer</h2> <ol> <li>Yes, it make sense, while <code>$(...)</code> or <code><code>...</code></code> stay usefull for returning result of a binary command or other strong script with a lot of bariables you won't inherit.</li> <li>Depending on your need and who wrote each parts... paralelism... other factors...</li> <li>Other alternatives, for dynamic command, not really, but don't miss to use <em>built-ins</em> like <code>mapfile</code> or <code>read -a</code> when you can.</li> </ol> <h2>Disclaimer</h2> <p>This concern <a href="/questions/tagged/bash" class="post-tag" title="show questions tagged 'bash'" rel="tag">bash</a> only! If you want your script to be <em>portable</em> (even if <code>bash</code> is already ported on most significant os), you have to not use <em>array variables</em> and try your script with <code>zsh</code> or <code>dash</code>.</p>

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