expr

<h2 id="overview">Overview</h2>
<p><i>expr</i> evaluates <a href="/facts/Integer/PUwwrawx">integer</a> or <a href="/facts/String_(computer_science)/4ChJu5WS">string</a> expressions, including pattern matching <a href="/facts/Regular_expression/KFL3veHX">regular expressions</a>. Each symbol (operator, value, etc.) in the <i>expression</i> must be given as a separate parameter. Most of the challenge posed in writing expressions is preventing the invoking <a href="/facts/Unix_shell/2G4T2Fb9">command line shell</a> from acting on characters intended for <i>expr</i> to process.
</p>
<h2 id="syntax">Syntax</h2>
<p>Syntax: expr <i>expression</i>
</p><p>The operators available
</p>
<ul><li>for integers:  addition, subtraction, multiplication, division and modulus</li>
<li>for strings:  match a regular expression; in some versions: find a set of characters in a string ("index"), find substring ("substr"), length of string ("length")</li>
<li>for either:  comparison (equal, not equal, less than, etc.)</li></ul>
<h2 id="example">Example</h2>
<p>The following is a (non-<a href="/facts/POSIX/mQkSt234">POSIX</a>-compliant) example involving <a href="/facts/Boolean_expression/qWS7Ef6n">Boolean expressions</a>:
</p>
expr length  "abcdef"  "<"  5  "|"  15  -  4  ">"  8

<p>This example outputs "1".  This is because length "abcdef"  is 6, which is not less than 5 (so the left side of the | returns zero).  But 15 minus 4 is 11 and is greater than 8, so the right side is true, which makes the <i>or</i> true, so 1 is the result. The program <a href="/facts/Exit_status/V3uTvuNo">exit status</a> is zero for this example.
</p><p>For pure arithmetic, it is often more convenient to use <a href="/facts/Bc_programming_language/8nUNyNeD">bc</a>.  For example:
</p>
echo "3 * 4 + 14 / 2" | bc

<p>since it accepts the expression as a single argument.
</p><p>For <a href="/facts/Software_portability/tWKVGCBb">portable</a> shell programming, use of the "index", "length", "match" and "substr" commands must be avoided; string matching remains possible but it must use the "string : regexp" syntax.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/List_of_Unix_commands/EEuIsUx9">List of Unix commands</a></li></ul>

<h2 id="external-links">External links</h2>

The Wikibook <i>Guide to Unix</i> has a page on the topic of: <i>Commands</i>

<ul><li><a href="https://pubs.opengroup.org/onlinepubs/9799919799/utilities/expr.html">expr</a>: evaluate arguments as an expression – Shell and Utilities Reference, <a href="/facts/Single_Unix_Specification/w1ba5bDt">The Single UNIX Specification</a>, Version 4 from <a href="/facts/The_Open_Group/uRoDdEae">The Open Group</a></li>
<li><a href="https://www.gnu.org/software/coreutils/manual/html_node/expr-invocation.html#expr-invocation">expr invocation in GNU coreutils manual</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Port of the most important GNU utilities to Windows <a href="https://sourceforge.net/projects/unxutils/" target="_blank">https://sourceforge.net/projects/unxutils/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Native Win32 ports of some GNU utilities". unxutils.sourceforge.net. <a href="http://unxutils.sourceforge.net/" target="_blank">http://unxutils.sourceforge.net/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Retrieved 2020-09-05. <a href="/wiki/IBM" target="_blank">/wiki/IBM</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

expr open-in-new

expr