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    <p>Upon executing a command as <code>$(command)</code> allows the <a href="http://www.gnu.org/software/bash/manual/bashref.html#Command-Substitution">output of the command to replace itself</a>.</p> <p>When you say:</p> <pre><code>a=$(false) # false fails; the output of false is stored in the variable a </code></pre> <p>the output produced by the command <code>false</code> is stored in the variable <code>a</code>. Moreover, the exit code is the same as produced by the command. <code>help false</code> would tell:</p> <pre><code>false: false Return an unsuccessful result. Exit Status: Always fails. </code></pre> <p>On the other hand, saying:</p> <pre><code>$ false # Exit code: 1 $ a="" # Exit code: 0 $ echo $? # Prints 0 </code></pre> <p>causes the exit code for the assignment to <code>a</code> to be returned which is <code>0</code>.</p> <hr> <p>EDIT: </p> <p>Quoting from the <a href="http://www.gnu.org/software/bash/manual/bashref.html#Simple-Command-Expansion">manual</a>:</p> <blockquote> <p>If one of the expansions contained a command substitution, the exit status of the command is the exit status of the last command substitution performed.</p> </blockquote> <p>Quoting from <a href="http://mywiki.wooledge.org/BashFAQ/002">BASHFAQ/002</a>:</p> <blockquote> <p><strong>How can I store the return value and/or output of a command in a variable?</strong></p> <p>...</p> <p><code>output=$(command)</code></p> <p><code>status=$?</code></p> <p>The assignment to <code>output</code> has no effect on <code>command</code>'s exit status, which is still in <code>$?</code>.</p> </blockquote>
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    1. POExit code of variable assignment to command substitution in Bash
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    1. COVery good answer :)! Can you please help me find out the reference of `the exit code is the same as produced by the command`, I spend a lot of time but did not get the result :(
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    2. CO@Reorx Added a couple of references in the edit above.
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    3. COThanks, that's clear enough :D
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