<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><emphasis>e</emphasis> <literal>.</literal> <emphasis>attrpath</emphasis> [ <literal>or</literal> <emphasis>def</emphasis> ] </entry> <entry>none</entry> <entry>Select attribute denoted by the attribute path <emphasis>attrpath</emphasis> from set <emphasis>e</emphasis>. (An attribute path is a dot-separated list of attribute names.) If the attribute doesn’t exist, return <emphasis>def</emphasis> if provided, otherwise abort evaluation.</entry> <entry>1</entry> </row> <row> <entry>Application</entry> <entry><emphasis>e1</emphasis> <emphasis>e2</emphasis></entry> <entry>left</entry> <entry>Call function <emphasis>e1</emphasis> with argument <emphasis>e2</emphasis>.</entry> <entry>2</entry> </row> <row> <entry>Arithmetic Negation</entry> <entry><literal>-</literal> <emphasis>e</emphasis></entry> <entry>none</entry> <entry>Arithmetic negation.</entry> <entry>3</entry> </row> <row> <entry>Has Attribute</entry> <entry><emphasis>e</emphasis> <literal>?</literal> <emphasis>attrpath</emphasis></entry> <entry>none</entry> <entry>Test whether set <emphasis>e</emphasis> contains the attribute denoted by <emphasis>attrpath</emphasis>; return <literal>true</literal> or <literal>false</literal>.</entry> <entry>4</entry> </row> <row> <entry>List Concatenation</entry> <entry><emphasis>e1</emphasis> <literal>++</literal> <emphasis>e2</emphasis></entry> <entry>right</entry> <entry>List concatenation.</entry> <entry>5</entry> </row> <row> <entry>Multiplication</entry> <entry> <emphasis>e1</emphasis> <literal>*</literal> <emphasis>e2</emphasis>, </entry> <entry>left</entry> <entry>Arithmetic multiplication.</entry> <entry>6</entry> </row> <row> <entry>Division</entry> <entry> <emphasis>e1</emphasis> <literal>/</literal> <emphasis>e2</emphasis> </entry> <entry>left</entry> <entry>Arithmetic division.</entry> <entry>6</entry> </row> <row> <entry>Addition</entry> <entry> <emphasis>e1</emphasis> <literal>+</literal> <emphasis>e2</emphasis> </entry> <entry>left</entry> <entry>Arithmetic addition.</entry> <entry>7</entry> </row> <row> <entry>Subtraction</entry> <entry> <emphasis>e1</emphasis> <literal>-</literal> <emphasis>e2</emphasis> </entry> <entry>left</entry> <entry>Arithmetic subtraction.</entry> <entry>7</entry> </row> <row> <entry>String Concatenation</entry> <entry> <emphasis>string1</emphasis> <literal>+</literal> <emphasis>string2</emphasis> </entry> <entry>left</entry> <entry>String concatenation.</entry> <entry>7</entry> </row> <row> <entry>Not</entry> <entry><literal>!</literal> <emphasis>e</emphasis></entry> <entry>none</entry> <entry>Boolean negation.</entry> <entry>8</entry> </row> <row> <entry>Update</entry> <entry><emphasis>e1</emphasis> <literal>//</literal> <emphasis>e2</emphasis></entry> <entry>right</entry> <entry>Return a set consisting of the attributes in <emphasis>e1</emphasis> and <emphasis>e2</emphasis> (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> <emphasis>e1</emphasis> <literal><</literal> <emphasis>e2</emphasis>, </entry> <entry>none</entry> <entry>Arithmetic comparison.</entry> <entry>10</entry> </row> <row> <entry>Less Than or Equal To</entry> <entry> <emphasis>e1</emphasis> <literal><=</literal> <emphasis>e2</emphasis> </entry> <entry>none</entry> <entry>Arithmetic comparison.</entry> <entry>10</entry> </row> <row> <entry>Greater Than</entry> <entry> <emphasis>e1</emphasis> <literal>></literal> <emphasis>e2</emphasis> </entry> <entry>none</entry> <entry>Arithmetic comparison.</entry> <entry>10</entry> </row> <row> <entry>Greater Than or Equal To</entry> <entry> <emphasis>e1</emphasis> <literal>>=</literal> <emphasis>e2</emphasis> </entry> <entry>none</entry> <entry>Arithmetic comparison.</entry> <entry>10</entry> </row> <row> <entry>Equality</entry> <entry> <emphasis>e1</emphasis> <literal>==</literal> <emphasis>e2</emphasis> </entry> <entry>none</entry> <entry>Equality.</entry> <entry>11</entry> </row> <row> <entry>Inequality</entry> <entry> <emphasis>e1</emphasis> <literal>!=</literal> <emphasis>e2</emphasis> </entry> <entry>none</entry> <entry>Inequality.</entry> <entry>11</entry> </row> <row> <entry>Logical AND</entry> <entry><emphasis>e1</emphasis> <literal>&&</literal> <emphasis>e2</emphasis></entry> <entry>left</entry> <entry>Logical AND.</entry> <entry>12</entry> </row> <row> <entry>Logical OR</entry> <entry><emphasis>e1</emphasis> <literal>||</literal> <emphasis>e2</emphasis></entry> <entry>left</entry> <entry>Logical OR.</entry> <entry>13</entry> </row> <row> <entry>Logical Implication</entry> <entry><emphasis>e1</emphasis> <literal>-></literal> <emphasis>e2</emphasis></entry> <entry>none</entry> <entry>Logical implication (equivalent to <literal>!<emphasis>e1</emphasis> || <emphasis>e2</emphasis></literal>).</entry> <entry>14</entry> </row> </tbody> </tgroup> </table> </section>