<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>Syntax</entry> <entry>Associativity</entry> <entry>Description</entry> </row> </thead> <tbody> <row> <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> </row> <row> <entry><replaceable>e1</replaceable> <replaceable>e2</replaceable></entry> <entry>left</entry> <entry>Call function <replaceable>e1</replaceable> with argument <replaceable>e2</replaceable>.</entry> </row> <row> <entry><literal>-</literal> <replaceable>e</replaceable></entry> <entry>none</entry> <entry>Arithmetic negation.</entry> </row> <row> <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> </row> <row> <entry><replaceable>e1</replaceable> <literal>++</literal> <replaceable>e2</replaceable></entry> <entry>right</entry> <entry>List concatenation.</entry> </row> <row> <entry> <replaceable>e1</replaceable> <literal>*</literal> <replaceable>e2</replaceable>, <replaceable>e1</replaceable> <literal>/</literal> <replaceable>e2</replaceable> </entry> <entry>left</entry> <entry>Arithmetic multiplication and division.</entry> </row> <row> <entry> <replaceable>e1</replaceable> <literal>+</literal> <replaceable>e2</replaceable>, <replaceable>e1</replaceable> <literal>-</literal> <replaceable>e2</replaceable> </entry> <entry>left</entry> <entry>Arithmetic addition and subtraction. String or path concatenation (only by <literal>+</literal>).</entry> </row> <row> <entry><literal>!</literal> <replaceable>e</replaceable></entry> <entry>none</entry> <entry>Boolean negation.</entry> </row> <row> <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> </row> <row> <entry> <replaceable>e1</replaceable> <literal><</literal> <replaceable>e2</replaceable>, <replaceable>e1</replaceable> <literal>></literal> <replaceable>e2</replaceable>, <replaceable>e1</replaceable> <literal><=</literal> <replaceable>e2</replaceable>, <replaceable>e1</replaceable> <literal>>=</literal> <replaceable>e2</replaceable> </entry> <entry>none</entry> <entry>Arithmetic comparison.</entry> </row> <row> <entry> <replaceable>e1</replaceable> <literal>==</literal> <replaceable>e2</replaceable>, <replaceable>e1</replaceable> <literal>!=</literal> <replaceable>e2</replaceable> </entry> <entry>none</entry> <entry>Equality and inequality.</entry> </row> <row> <entry><replaceable>e1</replaceable> <literal>&&</literal> <replaceable>e2</replaceable></entry> <entry>left</entry> <entry>Logical AND.</entry> </row> <row> <entry><replaceable>e1</replaceable> <literal>||</literal> <replaceable>e2</replaceable></entry> <entry>left</entry> <entry>Logical OR.</entry> </row> <row> <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> </row> </tbody> </tgroup> </table> </section>