<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-language-operators">
<title>Operators</title>
<para><xref linkend='table-operators' /> lists the operators in the
Nix expression language, in order of precedence (from strongest to
weakest binding).</para>
<table xml:id='table-operators'>
<title>Operators</title>
<tgroup cols='3'>
<thead>
<row>
<entry>Name</entry>
<entry>Syntax</entry>
<entry>Associativity</entry>
<entry>Description</entry>
<entry>Precedence</entry>
</row>
</thead>
<tbody>
<row>
<entry>Select</entry>
<entry><replaceable>e</replaceable> <literal>.</literal>
<replaceable>attrpath</replaceable>
[ <literal>or</literal> <replaceable>def</replaceable> ]
</entry>
<entry>none</entry>
<entry>Select attribute denoted by the attribute path
<replaceable>attrpath</replaceable> from set
<replaceable>e</replaceable>. (An attribute path is a
dot-separated list of attribute names.) If the attribute
doesn’t exist, return <replaceable>def</replaceable> if
provided, otherwise abort evaluation.</entry>
<entry>1</entry>
</row>
<row>
<entry>Application</entry>
<entry><replaceable>e1</replaceable> <replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Call function <replaceable>e1</replaceable> with
argument <replaceable>e2</replaceable>.</entry>
<entry>2</entry>
</row>
<row>
<entry>Arithmetic Negation</entry>
<entry><literal>-</literal> <replaceable>e</replaceable></entry>
<entry>none</entry>
<entry>Arithmetic negation.</entry>
<entry>3</entry>
</row>
<row>
<entry>Has Attribute</entry>
<entry><replaceable>e</replaceable> <literal>?</literal>
<replaceable>attrpath</replaceable></entry>
<entry>none</entry>
<entry>Test whether set <replaceable>e</replaceable> contains
the attribute denoted by <replaceable>attrpath</replaceable>;
return <literal>true</literal> or
<literal>false</literal>.</entry>
<entry>4</entry>
</row>
<row>
<entry>List Concatenation</entry>
<entry><replaceable>e1</replaceable> <literal>++</literal> <replaceable>e2</replaceable></entry>
<entry>right</entry>
<entry>List concatenation.</entry>
<entry>5</entry>
</row>
<row>
<entry>Multiplication</entry>
<entry>
<replaceable>e1</replaceable> <literal>*</literal> <replaceable>e2</replaceable>,
</entry>
<entry>left</entry>
<entry>Arithmetic multiplication.</entry>
<entry>6</entry>
</row>
<row>
<entry>Division</entry>
<entry>
<replaceable>e1</replaceable> <literal>/</literal> <replaceable>e2</replaceable>
</entry>
<entry>left</entry>
<entry>Arithmetic division.</entry>
<entry>6</entry>
</row>
<row>
<entry>Addition</entry>
<entry>
<replaceable>e1</replaceable> <literal>+</literal> <replaceable>e2</replaceable>
</entry>
<entry>left</entry>
<entry>Arithmetic addition.</entry>
<entry>7</entry>
</row>
<row>
<entry>Subtraction</entry>
<entry>
<replaceable>e1</replaceable> <literal>-</literal> <replaceable>e2</replaceable>
</entry>
<entry>left</entry>
<entry>Arithmetic subtraction.</entry>
<entry>7</entry>
</row>
<row>
<entry>String Concatenation</entry>
<entry>
<replaceable>string1</replaceable> <literal>+</literal> <replaceable>string2</replaceable>
</entry>
<entry>left</entry>
<entry>String concatenation.</entry>
<entry>7</entry>
</row>
<row>
<entry>Not</entry>
<entry><literal>!</literal> <replaceable>e</replaceable></entry>
<entry>none</entry>
<entry>Boolean negation.</entry>
<entry>8</entry>
</row>
<row>
<entry>Update</entry>
<entry><replaceable>e1</replaceable> <literal>//</literal>
<replaceable>e2</replaceable></entry>
<entry>right</entry>
<entry>Return a set consisting of the attributes in
<replaceable>e1</replaceable> and
<replaceable>e2</replaceable> (with the latter taking
precedence over the former in case of equally named
attributes).</entry>
<entry>9</entry>
</row>
<row>
<entry>Less Than</entry>
<entry>
<replaceable>e1</replaceable> <literal><</literal> <replaceable>e2</replaceable>,
</entry>
<entry>none</entry>
<entry>Arithmetic comparison.</entry>
<entry>10</entry>
</row>
<row>
<entry>Less Than or Equal To</entry>
<entry>
<replaceable>e1</replaceable> <literal><=</literal> <replaceable>e2</replaceable>
</entry>
<entry>none</entry>
<entry>Arithmetic comparison.</entry>
<entry>10</entry>
</row>
<row>
<entry>Greater Than</entry>
<entry>
<replaceable>e1</replaceable> <literal>></literal> <replaceable>e2</replaceable>
</entry>
<entry>none</entry>
<entry>Arithmetic comparison.</entry>
<entry>10</entry>
</row>
<row>
<entry>Greater Than or Equal To</entry>
<entry>
<replaceable>e1</replaceable> <literal>>=</literal> <replaceable>e2</replaceable>
</entry>
<entry>none</entry>
<entry>Arithmetic comparison.</entry>
<entry>10</entry>
</row>
<row>
<entry>Equality</entry>
<entry>
<replaceable>e1</replaceable> <literal>==</literal> <replaceable>e2</replaceable>
</entry>
<entry>none</entry>
<entry>Equality.</entry>
<entry>11</entry>
</row>
<row>
<entry>Inequality</entry>
<entry>
<replaceable>e1</replaceable> <literal>!=</literal> <replaceable>e2</replaceable>
</entry>
<entry>none</entry>
<entry>Inequality.</entry>
<entry>11</entry>
</row>
<row>
<entry>Logical AND</entry>
<entry><replaceable>e1</replaceable> <literal>&&</literal>
<replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Logical AND.</entry>
<entry>12</entry>
</row>
<row>
<entry>Logical OR</entry>
<entry><replaceable>e1</replaceable> <literal>||</literal>
<replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Logical OR.</entry>
<entry>13</entry>
</row>
<row>
<entry>Logical Implication</entry>
<entry><replaceable>e1</replaceable> <literal>-></literal>
<replaceable>e2</replaceable></entry>
<entry>none</entry>
<entry>Logical implication (equivalent to
<literal>!<replaceable>e1</replaceable> ||
<replaceable>e2</replaceable></literal>).</entry>
<entry>14</entry>
</row>
</tbody>
</tgroup>
</table>
</section>
