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|
||
|
||
<span class="md-ellipsis">
|
||
Aux
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--active md-nav__item--section md-nav__item--nested">
|
||
|
||
|
||
|
||
<input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_4" checked>
|
||
|
||
|
||
|
||
<div class="md-nav__link md-nav__container">
|
||
<a href="../../" class="md-nav__link ">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Lix
|
||
</span>
|
||
|
||
|
||
</a>
|
||
|
||
|
||
<label class="md-nav__link " for="__nav_4" id="__nav_4_label" tabindex="">
|
||
<span class="md-nav__icon md-icon"></span>
|
||
</label>
|
||
|
||
</div>
|
||
|
||
<nav class="md-nav" data-md-level="1" aria-labelledby="__nav_4_label" aria-expanded="true">
|
||
<label class="md-nav__title" for="__nav_4">
|
||
<span class="md-nav__icon md-icon"></span>
|
||
Lix
|
||
</label>
|
||
<ul class="md-nav__list" data-md-scrollfix>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../../glossary/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Glossary
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../../quick-start/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Quick Start
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../Advanced-Topics/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Advanced Topics
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../Command-Reference/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Command Reference
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../Package-Management/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Package Management
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../architecture/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Architecture
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../contributing/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Contributing
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../installation/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Installation
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--active md-nav__item--nested">
|
||
|
||
|
||
|
||
<input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_4_10" checked>
|
||
|
||
|
||
|
||
<div class="md-nav__link md-nav__container">
|
||
<a href="../" class="md-nav__link ">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Language
|
||
</span>
|
||
|
||
|
||
</a>
|
||
|
||
|
||
<label class="md-nav__link " for="__nav_4_10" id="__nav_4_10_label" tabindex="0">
|
||
<span class="md-nav__icon md-icon"></span>
|
||
</label>
|
||
|
||
</div>
|
||
|
||
<nav class="md-nav" data-md-level="2" aria-labelledby="__nav_4_10_label" aria-expanded="true">
|
||
<label class="md-nav__title" for="__nav_4_10">
|
||
<span class="md-nav__icon md-icon"></span>
|
||
Language
|
||
</label>
|
||
<ul class="md-nav__list" data-md-scrollfix>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../advanced-attributes/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Advanced Attributes
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../builtin-constants/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Built-in Constants
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--active">
|
||
|
||
<input class="md-nav__toggle md-toggle" type="checkbox" id="__toc">
|
||
|
||
|
||
|
||
|
||
|
||
<a href="./" class="md-nav__link md-nav__link--active">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Built-in Functions
|
||
</span>
|
||
|
||
|
||
</a>
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../constructs/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Language Constructs
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../derivations/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Derivations
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../operators/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Operators
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../string-interpolation/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
String interpolation
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item">
|
||
<a href="../values/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Data Types
|
||
</span>
|
||
|
||
|
||
</a>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
</ul>
|
||
</nav>
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../protocols/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Protocols
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../release-notes/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Release notes
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
</ul>
|
||
</nav>
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
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|
||
|
||
|
||
|
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|
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|
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|
||
|
||
|
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|
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|
||
|
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|
||
|
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|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../../NixOS/appstream/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
NixOS
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="md-nav__item md-nav__item--pruned md-nav__item--nested">
|
||
|
||
|
||
|
||
|
||
<a href="../../../Nixpkgs/" class="md-nav__link">
|
||
|
||
|
||
<span class="md-ellipsis">
|
||
Nixpkgs
|
||
</span>
|
||
|
||
|
||
|
||
<span class="md-nav__icon md-icon"></span>
|
||
|
||
</a>
|
||
|
||
|
||
|
||
</li>
|
||
|
||
|
||
|
||
</ul>
|
||
</nav>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
|
||
|
||
|
||
<div class="md-sidebar md-sidebar--secondary" data-md-component="sidebar" data-md-type="toc" >
|
||
<div class="md-sidebar__scrollwrap">
|
||
<div class="md-sidebar__inner">
|
||
|
||
|
||
<nav class="md-nav md-nav--secondary" aria-label="Table of contents">
|
||
|
||
|
||
|
||
|
||
|
||
|
||
</nav>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
|
||
|
||
|
||
<div class="md-content" data-md-component="content">
|
||
<article class="md-content__inner md-typeset">
|
||
|
||
|
||
|
||
|
||
<h1 id="built-in-functions">Built-in Functions</h1>
|
||
<p>This section lists the functions built into the Nix language evaluator.
|
||
All built-in functions are available through the global <a href="../builtin-constants/#builtins-builtins"><code>builtins</code></a> constant.</p>
|
||
<p>For convenience, some built-ins can be accessed directly:</p>
|
||
<ul>
|
||
<li><a href="#builtins-derivation"><code>derivation</code></a></li>
|
||
<li><a href="#builtins-import"><code>import</code></a></li>
|
||
<li><a href="#builtins-abort"><code>abort</code></a></li>
|
||
<li><a href="#builtins-throw"><code>throw</code></a></li>
|
||
</ul>
|
||
<dl>
|
||
<dt id="builtins-derivation"><a href="#builtins-derivation"><code>derivation <var>attrs</var></code></a></dt>
|
||
<dd><p><var>derivation</var> is described in
|
||
<a href="derivations.md">its own section</a>.</p></dd>
|
||
|
||
<dt id="builtins-abort">
|
||
<a href="#builtins-abort"><code>abort <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Abort Nix expression evaluation and print the error message *s*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-add">
|
||
<a href="#builtins-add"><code>add <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the sum of the numbers *e1* and *e2*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-addDrvOutputDependencies">
|
||
<a href="#builtins-addDrvOutputDependencies"><code>addDrvOutputDependencies <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Create a copy of the given string where a single constant string context element is turned into a "derivation deep" string context element.
|
||
|
||
The store path that is the constant string context element should point to a valid derivation, and end in `.drv`.
|
||
|
||
The original string context element must not be empty or have multiple elements, and it must not have any other type of element other than a constant or derivation deep element.
|
||
The latter is supported so this function is idempotent.
|
||
|
||
This is the opposite of [`builtins.unsafeDiscardOutputDependency`](#builtins-unsafeDiscardOutputDependency).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-all">
|
||
<a href="#builtins-all"><code>all <var>pred</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if the function *pred* returns `true` for all elements
|
||
of *list*, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-any">
|
||
<a href="#builtins-any"><code>any <var>pred</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if the function *pred* returns `true` for at least one
|
||
element of *list*, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-attrNames">
|
||
<a href="#builtins-attrNames"><code>attrNames <var>set</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the names of the attributes in the set *set* in an
|
||
alphabetically sorted list. For instance, `builtins.attrNames { y
|
||
= 1; x = "foo"; }` evaluates to `[ "x" "y" ]`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-attrValues">
|
||
<a href="#builtins-attrValues"><code>attrValues <var>set</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the values of the attributes in the set *set* in the order
|
||
corresponding to the sorted attribute names.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-baseNameOf">
|
||
<a href="#builtins-baseNameOf"><code>baseNameOf <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the *base name* of the string *s*, that is, everything
|
||
following the final slash in the string. This is similar to the GNU
|
||
`basename` command.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-bitAnd">
|
||
<a href="#builtins-bitAnd"><code>bitAnd <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the bitwise AND of the integers *e1* and *e2*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-bitOr">
|
||
<a href="#builtins-bitOr"><code>bitOr <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the bitwise OR of the integers *e1* and *e2*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-bitXor">
|
||
<a href="#builtins-bitXor"><code>bitXor <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the bitwise XOR of the integers *e1* and *e2*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-break">
|
||
<a href="#builtins-break"><code>break <var>v</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
In debug mode (enabled using `--debugger`), pause Nix expression evaluation and enter the REPL.
|
||
Otherwise, return the argument `v`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-catAttrs">
|
||
<a href="#builtins-catAttrs"><code>catAttrs <var>attr</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Collect each attribute named *attr* from a list of attribute
|
||
sets. Attrsets that don't contain the named attribute are
|
||
ignored. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>catAttrs <span class="s2">"a"</span> <span class="p">[{</span><span class="ss">a</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;}</span> <span class="p">{</span><span class="ss">b</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;}</span> <span class="p">{</span><span class="ss">a</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;}]</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to `[1 2]`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-ceil">
|
||
<a href="#builtins-ceil"><code>ceil <var>double</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Converts an IEEE-754 double-precision floating-point number (*double*) to
|
||
the next higher integer.
|
||
|
||
If the datatype is neither an integer nor a "float", an evaluation error will be
|
||
thrown.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-compareVersions">
|
||
<a href="#builtins-compareVersions"><code>compareVersions <var>s1</var> <var>s2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Compare two strings representing versions and return `-1` if
|
||
version *s1* is older than version *s2*, `0` if they are the same,
|
||
and `1` if *s1* is newer than *s2*. The version comparison
|
||
algorithm is the same as the one used by [`nix-env
|
||
-u`](../Command-Reference/nix-env/index.md#operation---upgrade).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-concatLists">
|
||
<a href="#builtins-concatLists"><code>concatLists <var>lists</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Concatenate a list of lists into a single list.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-concatMap">
|
||
<a href="#builtins-concatMap"><code>concatMap <var>f</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
This function is equivalent to `builtins.concatLists (map f list)`
|
||
but is more efficient.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-concatStringsSep">
|
||
<a href="#builtins-concatStringsSep"><code>concatStringsSep <var>separator</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Concatenate a list of strings with a separator between each
|
||
element, e.g. `concatStringsSep "/" ["usr" "local" "bin"] ==
|
||
"usr/local/bin"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-deepSeq">
|
||
<a href="#builtins-deepSeq"><code>deepSeq <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
This is like `seq e1 e2`, except that *e1* is evaluated *deeply*:
|
||
if it’s a list or set, its elements or attributes are also
|
||
evaluated recursively.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-dirOf">
|
||
<a href="#builtins-dirOf"><code>dirOf <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the directory part of the string *s*, that is, everything
|
||
before the final slash in the string. This is similar to the GNU
|
||
`dirname` command.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-div">
|
||
<a href="#builtins-div"><code>div <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the quotient of the numbers *e1* and *e2*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-elem">
|
||
<a href="#builtins-elem"><code>elem <var>x</var> <var>xs</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if a value equal to *x* occurs in the list *xs*, and
|
||
`false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-elemAt">
|
||
<a href="#builtins-elemAt"><code>elemAt <var>xs</var> <var>n</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return element *n* from the list *xs*. Elements are counted starting
|
||
from 0. A fatal error occurs if the index is out of bounds.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-fetchClosure">
|
||
<a href="#builtins-fetchClosure"><code>fetchClosure <var>args</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Fetch a store path [closure](../glossary.md#gloss-closure) from a binary cache, and return the store path as a string with context.
|
||
|
||
This function can be invoked in three ways, that we will discuss in order of preference.
|
||
|
||
**Fetch a content-addressed store path**
|
||
|
||
Example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchClosure <span class="p">{</span>
|
||
<span class="ss">fromStore</span> <span class="o">=</span> <span class="s2">"https://cache.nixos.org"</span><span class="p">;</span>
|
||
<span class="ss">fromPath</span> <span class="o">=</span> <span class="l">/nix/store/ldbhlwhh39wha58rm61bkiiwm6j7211j-git-2.33.1</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
This is the simplest invocation, and it does not require the user of the expression to configure [`trusted-public-keys`](../Command-Reference/conf-file.md#conf-trusted-public-keys) to ensure their authenticity.
|
||
|
||
If your store path is [input addressed](../glossary.md#gloss-input-addressed-store-object) instead of content addressed, consider the other two invocations.
|
||
|
||
**Fetch any store path and rewrite it to a fully content-addressed store path**
|
||
|
||
Example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchClosure <span class="p">{</span>
|
||
<span class="ss">fromStore</span> <span class="o">=</span> <span class="s2">"https://cache.nixos.org"</span><span class="p">;</span>
|
||
<span class="ss">fromPath</span> <span class="o">=</span> <span class="l">/nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1</span><span class="p">;</span>
|
||
<span class="ss">toPath</span> <span class="o">=</span> <span class="l">/nix/store/ldbhlwhh39wha58rm61bkiiwm6j7211j-git-2.33.1</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
This example fetches `/nix/store/r2jd...` from the specified binary cache,
|
||
and rewrites it into the content-addressed store path
|
||
`/nix/store/ldbh...`.
|
||
|
||
Like the previous example, no extra configuration or privileges are required.
|
||
|
||
To find out the correct value for `toPath` given a `fromPath`,
|
||
use [`nix store make-content-addressed`](../Command-Reference/New-CLI/nix3-store-make-content-addressed.md):
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="gp">#</span><span class="c1"># nix store make-content-addressed --from https://cache.nixos.org /nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1</span>
|
||
<span class="go">rewrote '/nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1' to '/nix/store/ldbhlwhh39wha58rm61bkiiwm6j7211j-git-2.33.1'</span>
|
||
</code></pre></div>
|
||
|
||
Alternatively, set `toPath = ""` and find the correct `toPath` in the error message.
|
||
|
||
**Fetch an input-addressed store path as is**
|
||
|
||
Example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchClosure <span class="p">{</span>
|
||
<span class="ss">fromStore</span> <span class="o">=</span> <span class="s2">"https://cache.nixos.org"</span><span class="p">;</span>
|
||
<span class="ss">fromPath</span> <span class="o">=</span> <span class="l">/nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1</span><span class="p">;</span>
|
||
<span class="ss">inputAddressed</span> <span class="o">=</span> <span class="no">true</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
It is possible to fetch an [input-addressed store path](../glossary.md#gloss-input-addressed-store-object) and return it as is.
|
||
However, this is the least preferred way of invoking `fetchClosure`, because it requires that the input-addressed paths are trusted by the Lix configuration.
|
||
|
||
**`builtins.storePath`**
|
||
|
||
`fetchClosure` is similar to [`builtins.storePath`](#builtins-storePath) in that it allows you to use a previously built store path in a Nix expression.
|
||
However, `fetchClosure` is more reproducible because it specifies a binary cache from which the path can be fetched.
|
||
Also, using content-addressed store paths does not require users to configure [`trusted-public-keys`](../Command-Reference/conf-file.md#conf-trusted-public-keys) to ensure their authenticity.
|
||
|
||
This function is only available if the [fetch-closure](../contributing/experimental-features.md#xp-feature-fetch-closure) experimental feature is enabled.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-fetchGit">
|
||
<a href="#builtins-fetchGit"><code>fetchGit <var>args</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Fetch a path from git. *args* can be a URL, in which case the HEAD
|
||
of the repo at that URL is fetched. Otherwise, it can be an
|
||
attribute with the following attributes (all except `url` optional):
|
||
|
||
- `url`
|
||
|
||
The URL of the repo.
|
||
|
||
- `name` (default: *basename of the URL*)
|
||
|
||
The name of the directory the repo should be exported to in the store.
|
||
|
||
- `rev` (default: *the tip of `ref`*)
|
||
|
||
The [Git revision] to fetch.
|
||
This is typically a commit hash.
|
||
|
||
[Git revision]: https://git-scm.com/docs/git-rev-parse#_specifying_revisions
|
||
|
||
- `ref` (default: `HEAD`)
|
||
|
||
The [Git reference] under which to look for the requested revision.
|
||
This is often a branch or tag name.
|
||
|
||
[Git reference]: https://git-scm.com/book/en/v2/Git-Internals-Git-References
|
||
|
||
By default, the `ref` value is prefixed with `refs/heads/`.
|
||
As of 2.3.0, Nix will not prefix `refs/heads/` if `ref` starts with `refs/`.
|
||
|
||
- `submodules` (default: `false`)
|
||
|
||
A Boolean parameter that specifies whether submodules should be checked out.
|
||
|
||
- `shallow` (default: `false`)
|
||
|
||
A Boolean parameter that specifies whether fetching from a shallow remote repository is allowed.
|
||
This still performs a full clone of what is available on the remote.
|
||
|
||
- `allRefs`
|
||
|
||
Whether to fetch all references of the repository.
|
||
With this argument being true, it's possible to load a `rev` from *any* `ref`
|
||
(by default only `rev`s from the specified `ref` are supported).
|
||
|
||
Here are some examples of how to use `fetchGit`.
|
||
|
||
- To fetch a private repository over SSH:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchGit <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"git@github.com:my-secret/repository.git"</span><span class="p">;</span>
|
||
<span class="ss">ref</span> <span class="o">=</span> <span class="s2">"master"</span><span class="p">;</span>
|
||
<span class="ss">rev</span> <span class="o">=</span> <span class="s2">"adab8b916a45068c044658c4158d81878f9ed1c3"</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
- To fetch an arbitrary reference:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchGit <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"https://github.com/NixOS/nix.git"</span><span class="p">;</span>
|
||
<span class="ss">ref</span> <span class="o">=</span> <span class="s2">"refs/heads/0.5-release"</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
- If the revision you're looking for is in the default branch of
|
||
the git repository you don't strictly need to specify the branch
|
||
name in the `ref` attribute.
|
||
|
||
However, if the revision you're looking for is in a future
|
||
branch for the non-default branch you will need to specify the
|
||
the `ref` attribute as well.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchGit <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"https://github.com/nixos/nix.git"</span><span class="p">;</span>
|
||
<span class="ss">rev</span> <span class="o">=</span> <span class="s2">"841fcbd04755c7a2865c51c1e2d3b045976b7452"</span><span class="p">;</span>
|
||
<span class="ss">ref</span> <span class="o">=</span> <span class="s2">"1.11-maintenance"</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
!!! note
|
||
> It is nice to always specify the branch which a revision
|
||
> belongs to. Without the branch being specified, the fetcher
|
||
> might fail if the default branch changes. Additionally, it can
|
||
> be confusing to try a commit from a non-default branch and see
|
||
> the fetch fail. If the branch is specified the fault is much
|
||
> more obvious.
|
||
|
||
- If the revision you're looking for is in the default branch of
|
||
the git repository you may omit the `ref` attribute.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchGit <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"https://github.com/nixos/nix.git"</span><span class="p">;</span>
|
||
<span class="ss">rev</span> <span class="o">=</span> <span class="s2">"841fcbd04755c7a2865c51c1e2d3b045976b7452"</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
- To fetch a specific tag:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchGit <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"https://github.com/nixos/nix.git"</span><span class="p">;</span>
|
||
<span class="ss">ref</span> <span class="o">=</span> <span class="s2">"refs/tags/1.9"</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
- To fetch the latest version of a remote branch:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchGit <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"ssh://git@github.com/nixos/nix.git"</span><span class="p">;</span>
|
||
<span class="ss">ref</span> <span class="o">=</span> <span class="s2">"master"</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
Nix will refetch the branch according to the [`tarball-ttl`](../Command-Reference/conf-file.md#conf-tarball-ttl) setting.
|
||
|
||
This behavior is disabled in [pure evaluation mode](../Command-Reference/conf-file.md#conf-pure-eval).
|
||
|
||
- To fetch the content of a checked-out work directory:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fetchGit <span class="l">./work-dir</span>
|
||
</code></pre></div>
|
||
|
||
If the URL points to a local directory, and no `ref` or `rev` is
|
||
given, `fetchGit` will use the current content of the checked-out
|
||
files, even if they are not committed or added to Git's index. It will
|
||
only consider files added to the Git repository, as listed by `git ls-files`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-fetchTarball">
|
||
<a href="#builtins-fetchTarball"><code>fetchTarball <var>args</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Download the specified URL, unpack it and return the path of the
|
||
unpacked tree. The file must be a tape archive (`.tar`) compressed
|
||
with `gzip`, `bzip2` or `xz`. The top-level path component of the
|
||
files in the tarball is removed, so it is best if the tarball
|
||
contains a single directory at top level. The typical use of the
|
||
function is to obtain external Nix expression dependencies, such as
|
||
a particular version of Nixpkgs, e.g.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="k">with</span> <span class="nb">import</span> <span class="p">(</span>fetchTarball <span class="s2">"https://github.com/NixOS/nixpkgs/archive/nixos-14.12.tar.gz"</span><span class="p">)</span> <span class="p">{};</span>
|
||
|
||
stdenv<span class="o">.</span>mkDerivation <span class="p">{</span> <span class="err">…</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
The fetched tarball is cached for a certain amount of time (1
|
||
hour by default) in `~/.cache/nix/tarballs/`. You can change the
|
||
cache timeout either on the command line with `--tarball-ttl`
|
||
*number-of-seconds* or in the Nix configuration file by adding
|
||
the line `tarball-ttl = ` *number-of-seconds*.
|
||
|
||
Note that when obtaining the hash with `nix-prefetch-url` the
|
||
option `--unpack` is required.
|
||
|
||
This function can also verify the contents against a hash. In that
|
||
case, the function takes a set instead of a URL. The set requires
|
||
the attribute `url` and the attribute `sha256`, e.g.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="k">with</span> <span class="nb">import</span> <span class="p">(</span>fetchTarball <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"https://github.com/NixOS/nixpkgs/archive/nixos-14.12.tar.gz"</span><span class="p">;</span>
|
||
<span class="ss">sha256</span> <span class="o">=</span> <span class="s2">"1jppksrfvbk5ypiqdz4cddxdl8z6zyzdb2srq8fcffr327ld5jj2"</span><span class="p">;</span>
|
||
<span class="p">})</span> <span class="p">{};</span>
|
||
|
||
stdenv<span class="o">.</span>mkDerivation <span class="p">{</span> <span class="err">…</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
Not available in [restricted evaluation mode](../Command-Reference/conf-file.md#conf-restrict-eval).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-fetchurl">
|
||
<a href="#builtins-fetchurl"><code>fetchurl <var>url</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Download the specified URL and return the path of the downloaded file.
|
||
|
||
Not available in [restricted evaluation mode](../Command-Reference/conf-file.md#conf-restrict-eval).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-filter">
|
||
<a href="#builtins-filter"><code>filter <var>f</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a list consisting of the elements of *list* for which the
|
||
function *f* returns `true`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-filterSource">
|
||
<a href="#builtins-filterSource"><code>filterSource <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
!!! warning
|
||
>
|
||
> `filterSource` should not be used to filter store paths. Since
|
||
> `filterSource` uses the name of the input directory while naming
|
||
> the output directory, doing so will produce a directory name in
|
||
> the form of `<hash2>-<hash>-<name>`, where `<hash>-<name>` is
|
||
> the name of the input directory. Since `<hash>` depends on the
|
||
> unfiltered directory, the name of the output directory will
|
||
> indirectly depend on files that are filtered out by the
|
||
> function. This will trigger a rebuild even when a filtered out
|
||
> file is changed. Use `builtins.path` instead, which allows
|
||
> specifying the name of the output directory.
|
||
|
||
This function allows you to copy sources into the Nix store while
|
||
filtering certain files. For instance, suppose that you want to use
|
||
the directory `source-dir` as an input to a Nix expression, e.g.
|
||
|
||
<div class="highlight"><pre><span></span><code>stdenv<span class="o">.</span>mkDerivation <span class="p">{</span>
|
||
<span class="o">...</span>
|
||
<span class="ss">src</span> <span class="o">=</span> <span class="l">./source-dir</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
However, if `source-dir` is a Subversion working copy, then all
|
||
those annoying `.svn` subdirectories will also be copied to the
|
||
store. Worse, the contents of those directories may change a lot,
|
||
causing lots of spurious rebuilds. With `filterSource` you can
|
||
filter out the `.svn` directories:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="ss">src</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>filterSource
|
||
<span class="p">(</span>path<span class="p">:</span> type<span class="p">:</span> type <span class="o">!=</span> <span class="s2">"directory"</span> <span class="o">||</span> <span class="nb">baseNameOf</span> path <span class="o">!=</span> <span class="s2">".svn"</span><span class="p">)</span>
|
||
<span class="l">./source-dir</span><span class="p">;</span>
|
||
</code></pre></div>
|
||
|
||
Thus, the first argument *e1* must be a predicate function that is
|
||
called for each regular file, directory or symlink in the source
|
||
tree *e2*. If the function returns `true`, the file is copied to the
|
||
Nix store, otherwise it is omitted. The function is called with two
|
||
arguments. The first is the full path of the file. The second is a
|
||
string that identifies the type of the file, which is either
|
||
`"regular"`, `"directory"`, `"symlink"` or `"unknown"` (for other
|
||
kinds of files such as device nodes or fifos — but note that those
|
||
cannot be copied to the Nix store, so if the predicate returns
|
||
`true` for them, the copy will fail). If you exclude a directory,
|
||
the entire corresponding subtree of *e2* will be excluded.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-findFile">
|
||
<a href="#builtins-findFile"><code>findFile <var>search path</var> <var>lookup path</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Look up the given path with the given search path.
|
||
|
||
A search path is represented list of [attribute sets](./values.md#attribute-set) with two attributes, `prefix`, and `path`.
|
||
`prefix` is a relative path.
|
||
`path` denotes a file system location; the exact syntax depends on the command line interface.
|
||
|
||
Examples of search path attribute sets:
|
||
|
||
- ```
|
||
{
|
||
prefix = "nixos-config";
|
||
path = "/etc/nixos/configuration.nix";
|
||
}
|
||
```
|
||
|
||
- ```
|
||
{
|
||
prefix = "";
|
||
path = "/nix/var/nix/profiles/per-user/root/channels";
|
||
}
|
||
```
|
||
|
||
The lookup algorithm checks each entry until a match is found, returning a [path value](../language/values.md#type-path) of the match.
|
||
|
||
This is the process for each entry:
|
||
If the lookup path matches `prefix`, then the remainder of the lookup path (the "suffix") is searched for within the directory denoted by `patch`.
|
||
Note that the `path` may need to be downloaded at this point to look inside.
|
||
If the suffix is found inside that directory, then the entry is a match;
|
||
the combined absolute path of the directory (now downloaded if need be) and the suffix is returned.
|
||
|
||
The syntax
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="l"><nixpkgs></span>
|
||
</code></pre></div>
|
||
|
||
is equivalent to:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>findFile <span class="nb">builtins</span><span class="o">.</span>nixPath <span class="s2">"nixpkgs"</span>
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-flakeRefToString">
|
||
<a href="#builtins-flakeRefToString"><code>flakeRefToString <var>attrs</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Convert a flake reference from attribute set format to URL format.
|
||
|
||
For example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>flakeRefToString <span class="p">{</span>
|
||
<span class="ss">dir</span> <span class="o">=</span> <span class="s2">"lib"</span><span class="p">;</span> <span class="ss">owner</span> <span class="o">=</span> <span class="s2">"NixOS"</span><span class="p">;</span> <span class="ss">ref</span> <span class="o">=</span> <span class="s2">"23.05"</span><span class="p">;</span> <span class="ss">repo</span> <span class="o">=</span> <span class="s2">"nixpkgs"</span><span class="p">;</span> <span class="ss">type</span> <span class="o">=</span> <span class="s2">"github"</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="s2">"github:NixOS/nixpkgs/23.05?dir=lib"</span>
|
||
</code></pre></div>
|
||
|
||
This function is only available if the [flakes](../contributing/experimental-features.md#xp-feature-flakes) experimental feature is enabled.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-floor">
|
||
<a href="#builtins-floor"><code>floor <var>double</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Converts an IEEE-754 double-precision floating-point number (*double*) to
|
||
the next lower integer.
|
||
|
||
If the datatype is neither an integer nor a "float", an evaluation error will be
|
||
thrown.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-foldl'">
|
||
<a href="#builtins-foldl'"><code>foldl' <var>op</var> <var>nul</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Reduce a list by applying a binary operator, from left to right,
|
||
e.g. `foldl' op nul [x0 x1 x2 ...] = op (op (op nul x0) x1) x2)
|
||
...`. For example, `foldl' (x: y: x + y) 0 [1 2 3]` evaluates to 6.
|
||
The return value of each application of `op` is evaluated immediately,
|
||
even for intermediate values.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-fromJSON">
|
||
<a href="#builtins-fromJSON"><code>fromJSON <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Convert a JSON string to a Nix value. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fromJSON <span class="s s-Multiline">''{"x": [1, 2, 3], "y": null}''</span>
|
||
</code></pre></div>
|
||
|
||
returns the value `{ x = [ 1 2 3 ]; y = null; }`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-fromTOML">
|
||
<a href="#builtins-fromTOML"><code>fromTOML <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Convert a TOML string to a Nix value. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>fromTOML <span class="s s-Multiline">''</span>
|
||
<span class="s s-Multiline"> x=1</span>
|
||
<span class="s s-Multiline"> s="a"</span>
|
||
<span class="s s-Multiline"> [table]</span>
|
||
<span class="s s-Multiline"> y=2</span>
|
||
<span class="s s-Multiline">''</span>
|
||
</code></pre></div>
|
||
|
||
returns the value `{ s = "a"; table = { y = 2; }; x = 1; }`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-functionArgs">
|
||
<a href="#builtins-functionArgs"><code>functionArgs <var>f</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a set containing the names of the formal arguments expected
|
||
by the function *f*. The value of each attribute is a Boolean
|
||
denoting whether the corresponding argument has a default value. For
|
||
instance, `functionArgs ({ x, y ? 123}: ...) = { x = false; y =
|
||
true; }`.
|
||
|
||
"Formal argument" here refers to the attributes pattern-matched by
|
||
the function. Plain lambdas are not included, e.g. `functionArgs (x:
|
||
...) = { }`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-genList">
|
||
<a href="#builtins-genList"><code>genList <var>generator</var> <var>length</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Generate list of size *length*, with each element *i* equal to the
|
||
value returned by *generator* `i`. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>genList <span class="p">(</span>x<span class="p">:</span> x <span class="o">*</span> x<span class="p">)</span> <span class="mi">5</span>
|
||
</code></pre></div>
|
||
|
||
returns the list `[ 0 1 4 9 16 ]`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-genericClosure">
|
||
<a href="#builtins-genericClosure"><code>genericClosure <var>attrset</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Take an *attrset* with values named `startSet` and `operator` in order to
|
||
return a *list of attrsets* by starting with the `startSet` and recursively
|
||
applying the `operator` function to each `item`. The *attrsets* in the
|
||
`startSet` and the *attrsets* produced by `operator` must contain a value
|
||
named `key` which is comparable. The result is produced by calling `operator`
|
||
for each `item` with a value for `key` that has not been called yet including
|
||
newly produced `item`s. The function terminates when no new `item`s are
|
||
produced. The resulting *list of attrsets* contains only *attrsets* with a
|
||
unique key. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code>builtins.genericClosure {
|
||
startSet = [ {key = 5;} ];
|
||
operator = item: [{
|
||
key = if (item.key / 2 ) * 2 == item.key
|
||
then item.key / 2
|
||
else 3 * item.key + 1;
|
||
}];
|
||
}
|
||
</code></pre></div>
|
||
evaluates to
|
||
<div class="highlight"><pre><span></span><code>[ { key = 5; } { key = 16; } { key = 8; } { key = 4; } { key = 2; } { key = 1; } ]
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-getAttr">
|
||
<a href="#builtins-getAttr"><code>getAttr <var>s</var> <var>set</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
`getAttr` returns the attribute named *s* from *set*. Evaluation
|
||
aborts if the attribute doesn’t exist. This is a dynamic version of
|
||
the `.` operator, since *s* is an expression rather than an
|
||
identifier.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-getContext">
|
||
<a href="#builtins-getContext"><code>getContext <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the string context of *s*.
|
||
|
||
The string context tracks references to derivations within a string.
|
||
It is represented as an attribute set of [store derivation](../glossary.md#gloss-store-derivation) paths mapping to output names.
|
||
|
||
Using [string interpolation](../language/string-interpolation.md) on a derivation will add that derivation to the string context.
|
||
For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>getContext <span class="s2">"</span><span class="si">${</span><span class="nb">derivation</span> <span class="p">{</span> <span class="ss">name</span> <span class="o">=</span> <span class="s2">"a"</span><span class="p">;</span> <span class="ss">builder</span> <span class="o">=</span> <span class="s2">"b"</span><span class="p">;</span> <span class="ss">system</span> <span class="o">=</span> <span class="s2">"c"</span><span class="p">;</span> <span class="p">}</span><span class="si">}</span><span class="s2">"</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to
|
||
|
||
<div class="highlight"><pre><span></span><code>{ "/nix/store/arhvjaf6zmlyn8vh8fgn55rpwnxq0n7l-a.drv" = { outputs = [ "out" ]; }; }
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-getEnv">
|
||
<a href="#builtins-getEnv"><code>getEnv <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
`getEnv` returns the value of the environment variable *s*, or an
|
||
empty string if the variable doesn’t exist. This function should be
|
||
used with care, as it can introduce all sorts of nasty environment
|
||
dependencies in your Nix expression.
|
||
|
||
`getEnv` is used in Nix Packages to locate the file
|
||
`~/.nixpkgs/config.nix`, which contains user-local settings for Nix
|
||
Packages. (That is, it does a `getEnv "HOME"` to locate the user’s
|
||
home directory.)
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-getFlake">
|
||
<a href="#builtins-getFlake"><code>getFlake <var>args</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Fetch a flake from a flake reference, and return its output attributes and some metadata. For example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">(</span><span class="nb">builtins</span><span class="o">.</span>getFlake <span class="s2">"nix/55bc52401966fbffa525c574c14f67b00bc4fb3a"</span><span class="p">)</span><span class="o">.</span>packages<span class="o">.</span>x86_64-linux<span class="o">.</span>nix
|
||
</code></pre></div>
|
||
|
||
Unless impure evaluation is allowed (`--impure`), the flake reference
|
||
must be "locked", e.g. contain a Git revision or content hash. An
|
||
example of an unlocked usage is:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">(</span><span class="nb">builtins</span><span class="o">.</span>getFlake <span class="s2">"github:edolstra/dwarffs"</span><span class="p">)</span><span class="o">.</span>rev
|
||
</code></pre></div>
|
||
|
||
This function is only available if the [flakes](../contributing/experimental-features.md#xp-feature-flakes) experimental feature is enabled.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-groupBy">
|
||
<a href="#builtins-groupBy"><code>groupBy <var>f</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Groups elements of *list* together by the string returned from the
|
||
function *f* called on each element. It returns an attribute set
|
||
where each attribute value contains the elements of *list* that are
|
||
mapped to the same corresponding attribute name returned by *f*.
|
||
|
||
For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>groupBy <span class="p">(</span><span class="nb">builtins</span><span class="o">.</span>substring <span class="mi">0</span> <span class="mi">1</span><span class="p">)</span> <span class="p">[</span><span class="s2">"foo"</span> <span class="s2">"bar"</span> <span class="s2">"baz"</span><span class="p">]</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">{</span> <span class="ss">b</span> <span class="o">=</span> <span class="p">[</span> <span class="s2">"bar"</span> <span class="s2">"baz"</span> <span class="p">];</span> <span class="ss">f</span> <span class="o">=</span> <span class="p">[</span> <span class="s2">"foo"</span> <span class="p">];</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-hasAttr">
|
||
<a href="#builtins-hasAttr"><code>hasAttr <var>s</var> <var>set</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
`hasAttr` returns `true` if *set* has an attribute named *s*, and
|
||
`false` otherwise. This is a dynamic version of the `?` operator,
|
||
since *s* is an expression rather than an identifier.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-hasContext">
|
||
<a href="#builtins-hasContext"><code>hasContext <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if string *s* has a non-empty context.
|
||
The context can be obtained with
|
||
[`getContext`](#builtins-getContext).
|
||
|
||
> **Example**
|
||
>
|
||
> Many operations require a string context to be empty because they are intended only to work with "regular" strings, and also to help users avoid unintentionally losing track of string context elements.
|
||
> `builtins.hasContext` can help create better domain-specific errors in those case.
|
||
>
|
||
> <div class="highlight"><pre><span></span><code>name<span class="p">:</span> meta<span class="p">:</span>
|
||
|
||
<span class="k">if</span> <span class="nb">builtins</span><span class="o">.</span>hasContext name
|
||
<span class="k">then</span> <span class="nb">throw</span> <span class="s2">"package name cannot contain string context"</span>
|
||
<span class="k">else</span> <span class="p">{</span> <span class="si">${</span>name<span class="si">}</span> <span class="o">=</span> meta<span class="p">;</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-hashFile">
|
||
<a href="#builtins-hashFile"><code>hashFile <var>type</var> <var>p</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a base-16 representation of the cryptographic hash of the
|
||
file at path *p*. The hash algorithm specified by *type* must be one
|
||
of `"md5"`, `"sha1"`, `"sha256"` or `"sha512"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-hashString">
|
||
<a href="#builtins-hashString"><code>hashString <var>type</var> <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a base-16 representation of the cryptographic hash of string
|
||
*s*. The hash algorithm specified by *type* must be one of `"md5"`,
|
||
`"sha1"`, `"sha256"` or `"sha512"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-head">
|
||
<a href="#builtins-head"><code>head <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the first element of a list; abort evaluation if the argument
|
||
isn’t a list or is an empty list. You can test whether a list is
|
||
empty by comparing it with `[]`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-import">
|
||
<a href="#builtins-import"><code>import <var>path</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Load, parse and return the Nix expression in the file *path*.
|
||
|
||
The value *path* can be a path, a string, or an attribute set with an
|
||
`__toString` attribute or a `outPath` attribute (as derivations or flake
|
||
inputs typically have).
|
||
|
||
If *path* is a directory, the file `default.nix` in that directory
|
||
is loaded.
|
||
|
||
Evaluation aborts if the file doesn’t exist or contains
|
||
an incorrect Nix expression. `import` implements Nix’s module
|
||
system: you can put any Nix expression (such as a set or a
|
||
function) in a separate file, and use it from Nix expressions in
|
||
other files.
|
||
|
||
!!! note
|
||
Unlike some languages, `import` is a regular function in Nix.
|
||
Paths using the angle bracket syntax (e.g., `import` *<foo>*)
|
||
are normal [path values](../language/values.md#type-path).
|
||
|
||
A Nix expression loaded by `import` must not contain any *free
|
||
variables* (identifiers that are not defined in the Nix expression
|
||
itself and are not built-in). Therefore, it cannot refer to
|
||
variables that are in scope at the call site. For instance, if you
|
||
have a calling expression
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="k">rec</span> <span class="p">{</span>
|
||
<span class="ss">x</span> <span class="o">=</span> <span class="mi">123</span><span class="p">;</span>
|
||
<span class="ss">y</span> <span class="o">=</span> <span class="nb">import</span> <span class="l">./foo.nix</span><span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
then the following `foo.nix` will give an error:
|
||
|
||
<div class="highlight"><pre><span></span><code>x <span class="o">+</span> <span class="mi">456</span>
|
||
</code></pre></div>
|
||
|
||
since `x` is not in scope in `foo.nix`. If you want `x` to be
|
||
available in `foo.nix`, you should pass it as a function argument:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="k">rec</span> <span class="p">{</span>
|
||
<span class="ss">x</span> <span class="o">=</span> <span class="mi">123</span><span class="p">;</span>
|
||
<span class="ss">y</span> <span class="o">=</span> <span class="nb">import</span> <span class="l">./foo.nix</span> x<span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
and
|
||
|
||
<div class="highlight"><pre><span></span><code>x<span class="p">:</span> x <span class="o">+</span> <span class="mi">456</span>
|
||
</code></pre></div>
|
||
|
||
(The function argument doesn’t have to be called `x` in `foo.nix`;
|
||
any name would work.)
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-intersectAttrs">
|
||
<a href="#builtins-intersectAttrs"><code>intersectAttrs <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a set consisting of the attributes in the set *e2* which have the
|
||
same name as some attribute in *e1*.
|
||
|
||
Performs in O(*n* log *m*) where *n* is the size of the smaller set and *m* the larger set's size.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isAttrs">
|
||
<a href="#builtins-isAttrs"><code>isAttrs <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to a set, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isBool">
|
||
<a href="#builtins-isBool"><code>isBool <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to a bool, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isFloat">
|
||
<a href="#builtins-isFloat"><code>isFloat <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to a float, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isFunction">
|
||
<a href="#builtins-isFunction"><code>isFunction <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to a function, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isInt">
|
||
<a href="#builtins-isInt"><code>isInt <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to an integer, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isList">
|
||
<a href="#builtins-isList"><code>isList <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to a list, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isNull">
|
||
<a href="#builtins-isNull"><code>isNull <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to `null`, and `false` otherwise.
|
||
|
||
This is equivalent to `e == null`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isPath">
|
||
<a href="#builtins-isPath"><code>isPath <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to a path, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-isString">
|
||
<a href="#builtins-isString"><code>isString <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if *e* evaluates to a string, and `false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-length">
|
||
<a href="#builtins-length"><code>length <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the length of the list *e*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-lessThan">
|
||
<a href="#builtins-lessThan"><code>lessThan <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if the number *e1* is less than the number *e2*, and
|
||
`false` otherwise. Evaluation aborts if either *e1* or *e2* does not
|
||
evaluate to a number.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-listToAttrs">
|
||
<a href="#builtins-listToAttrs"><code>listToAttrs <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Construct a set from a list specifying the names and values of each
|
||
attribute. Each element of the list should be a set consisting of a
|
||
string-valued attribute `name` specifying the name of the attribute,
|
||
and an attribute `value` specifying its value.
|
||
|
||
In case of duplicate occurrences of the same name, the first
|
||
takes precedence.
|
||
|
||
Example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>listToAttrs
|
||
<span class="p">[</span> <span class="p">{</span> <span class="ss">name</span> <span class="o">=</span> <span class="s2">"foo"</span><span class="p">;</span> <span class="ss">value</span> <span class="o">=</span> <span class="mi">123</span><span class="p">;</span> <span class="p">}</span>
|
||
<span class="p">{</span> <span class="ss">name</span> <span class="o">=</span> <span class="s2">"bar"</span><span class="p">;</span> <span class="ss">value</span> <span class="o">=</span> <span class="mi">456</span><span class="p">;</span> <span class="p">}</span>
|
||
<span class="p">{</span> <span class="ss">name</span> <span class="o">=</span> <span class="s2">"bar"</span><span class="p">;</span> <span class="ss">value</span> <span class="o">=</span> <span class="mi">420</span><span class="p">;</span> <span class="p">}</span>
|
||
<span class="p">]</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">{</span> <span class="ss">foo</span> <span class="o">=</span> <span class="mi">123</span><span class="p">;</span> <span class="ss">bar</span> <span class="o">=</span> <span class="mi">456</span><span class="p">;</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-map">
|
||
<a href="#builtins-map"><code>map <var>f</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Apply the function *f* to each element in the list *list*. For
|
||
example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">map</span> <span class="p">(</span>x<span class="p">:</span> <span class="s2">"foo"</span> <span class="o">+</span> x<span class="p">)</span> <span class="p">[</span> <span class="s2">"bar"</span> <span class="s2">"bla"</span> <span class="s2">"abc"</span> <span class="p">]</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to `[ "foobar" "foobla" "fooabc" ]`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-mapAttrs">
|
||
<a href="#builtins-mapAttrs"><code>mapAttrs <var>f</var> <var>attrset</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Apply function *f* to every element of *attrset*. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>mapAttrs <span class="p">(</span>name<span class="p">:</span> value<span class="p">:</span> value <span class="o">*</span> <span class="mi">10</span><span class="p">)</span> <span class="p">{</span> <span class="ss">a</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span> <span class="ss">b</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to `{ a = 10; b = 20; }`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-match">
|
||
<a href="#builtins-match"><code>match <var>regex</var> <var>str</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Returns a list if the [extended POSIX regular
|
||
expression](http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04)
|
||
*regex* matches *str* precisely, otherwise returns `null`. Each item
|
||
in the list is a regex group.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>match <span class="s2">"ab"</span> <span class="s2">"abc"</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `null`.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>match <span class="s2">"abc"</span> <span class="s2">"abc"</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `[ ]`.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>match <span class="s2">"a(b)(c)"</span> <span class="s2">"abc"</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `[ "b" "c" ]`.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>match <span class="s2">"[[:space:]]+([[:upper:]]+)[[:space:]]+"</span> <span class="s2">" FOO "</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `[ "FOO" ]`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-mul">
|
||
<a href="#builtins-mul"><code>mul <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the product of the numbers *e1* and *e2*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-outputOf">
|
||
<a href="#builtins-outputOf"><code>outputOf <var>derivation-reference</var> <var>output-name</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the output path of a derivation, literally or using a placeholder if needed.
|
||
|
||
If the derivation has a statically-known output path (i.e. the derivation output is input-addressed, or fixed content-addresed), the output path will just be returned.
|
||
But if the derivation is content-addressed or if the derivation is itself not-statically produced (i.e. is the output of another derivation), a placeholder will be returned instead.
|
||
|
||
*`derivation reference`* must be a string that may contain a regular store path to a derivation, or may be a placeholder reference. If the derivation is produced by a derivation, you must explicitly select `drv.outPath`.
|
||
This primop can be chained arbitrarily deeply.
|
||
For instance,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>outputOf
|
||
<span class="p">(</span><span class="nb">builtins</span><span class="o">.</span>outputOf myDrv <span class="s2">"out)</span>
|
||
<span class="s2"> "</span>out<span class="s2">"</span>
|
||
</code></pre></div>
|
||
|
||
will return a placeholder for the output of the output of `myDrv`.
|
||
|
||
This primop corresponds to the `^` sigil for derivable paths, e.g. as part of installable syntax on the command line.
|
||
|
||
This function is only available if the [dynamic-derivations](../contributing/experimental-features.md#xp-feature-dynamic-derivations) experimental feature is enabled.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-parseDrvName">
|
||
<a href="#builtins-parseDrvName"><code>parseDrvName <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Split the string *s* into a package name and version. The package
|
||
name is everything up to but not including the first dash not followed
|
||
by a letter, and the version is everything following that dash. The
|
||
result is returned in a set `{ name, version }`. Thus,
|
||
`builtins.parseDrvName "nix-0.12pre12876"` returns `{ name =
|
||
"nix"; version = "0.12pre12876"; }`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-parseFlakeRef">
|
||
<a href="#builtins-parseFlakeRef"><code>parseFlakeRef <var>flake-ref</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Parse a flake reference, and return its exploded form.
|
||
|
||
For example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>parseFlakeRef <span class="s2">"github:NixOS/nixpkgs/23.05?dir=lib"</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">{</span> <span class="ss">dir</span> <span class="o">=</span> <span class="s2">"lib"</span><span class="p">;</span> <span class="ss">owner</span> <span class="o">=</span> <span class="s2">"NixOS"</span><span class="p">;</span> <span class="ss">ref</span> <span class="o">=</span> <span class="s2">"23.05"</span><span class="p">;</span> <span class="ss">repo</span> <span class="o">=</span> <span class="s2">"nixpkgs"</span><span class="p">;</span> <span class="ss">type</span> <span class="o">=</span> <span class="s2">"github"</span><span class="p">;</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
This function is only available if the [flakes](../contributing/experimental-features.md#xp-feature-flakes) experimental feature is enabled.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-partition">
|
||
<a href="#builtins-partition"><code>partition <var>pred</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Given a predicate function *pred*, this function returns an
|
||
attrset containing a list named `right`, containing the elements
|
||
in *list* for which *pred* returned `true`, and a list named
|
||
`wrong`, containing the elements for which it returned
|
||
`false`. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>partition <span class="p">(</span>x<span class="p">:</span> x <span class="o">></span> <span class="mi">10</span><span class="p">)</span> <span class="p">[</span><span class="mi">1</span> <span class="mi">23</span> <span class="mi">9</span> <span class="mi">3</span> <span class="mi">42</span><span class="p">]</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">{</span> <span class="ss">right</span> <span class="o">=</span> <span class="p">[</span> <span class="mi">23</span> <span class="mi">42</span> <span class="p">];</span> <span class="ss">wrong</span> <span class="o">=</span> <span class="p">[</span> <span class="mi">1</span> <span class="mi">9</span> <span class="mi">3</span> <span class="p">];</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-path">
|
||
<a href="#builtins-path"><code>path <var>args</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
An enrichment of the built-in path type, based on the attributes
|
||
present in *args*. All are optional except `path`:
|
||
|
||
- path
|
||
The underlying path.
|
||
|
||
- name
|
||
The name of the path when added to the store. This can used to
|
||
reference paths that have nix-illegal characters in their names,
|
||
like `@`.
|
||
|
||
- filter
|
||
A function of the type expected by `builtins.filterSource`,
|
||
with the same semantics.
|
||
|
||
- recursive
|
||
When `false`, when `path` is added to the store it is with a
|
||
flat hash, rather than a hash of the NAR serialization of the
|
||
file. Thus, `path` must refer to a regular file, not a
|
||
directory. This allows similar behavior to `fetchurl`. Defaults
|
||
to `true`.
|
||
|
||
- sha256
|
||
When provided, this is the expected hash of the file at the
|
||
path. Evaluation will fail if the hash is incorrect, and
|
||
providing a hash allows `builtins.path` to be used even when the
|
||
`pure-eval` nix config option is on.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-pathExists">
|
||
<a href="#builtins-pathExists"><code>pathExists <var>path</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return `true` if the path *path* exists at evaluation time, and
|
||
`false` otherwise.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-placeholder">
|
||
<a href="#builtins-placeholder"><code>placeholder <var>output</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a placeholder string for the specified *output* that will be
|
||
substituted by the corresponding output path at build time. Typical
|
||
outputs would be `"out"`, `"bin"` or `"dev"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-readDir">
|
||
<a href="#builtins-readDir"><code>readDir <var>path</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the contents of the directory *path* as a set mapping
|
||
directory entries to the corresponding file type. For instance, if
|
||
directory `A` contains a regular file `B` and another directory
|
||
`C`, then `builtins.readDir ./A` will return the set
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">{</span> <span class="ss">B</span> <span class="o">=</span> <span class="s2">"regular"</span><span class="p">;</span> <span class="ss">C</span> <span class="o">=</span> <span class="s2">"directory"</span><span class="p">;</span> <span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
The possible values for the file type are `"regular"`,
|
||
`"directory"`, `"symlink"` and `"unknown"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-readFile">
|
||
<a href="#builtins-readFile"><code>readFile <var>path</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the contents of the file *path* as a string.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-readFileType">
|
||
<a href="#builtins-readFileType"><code>readFileType <var>p</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Determine the directory entry type of a filesystem node, being
|
||
one of "directory", "regular", "symlink", or "unknown".
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-removeAttrs">
|
||
<a href="#builtins-removeAttrs"><code>removeAttrs <var>set</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Remove the attributes listed in *list* from *set*. The attributes
|
||
don’t have to exist in *set*. For instance,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">removeAttrs</span> <span class="p">{</span> <span class="ss">x</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span> <span class="ss">y</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span> <span class="ss">z</span> <span class="o">=</span> <span class="mi">3</span><span class="p">;</span> <span class="p">}</span> <span class="p">[</span> <span class="s2">"a"</span> <span class="s2">"x"</span> <span class="s2">"z"</span> <span class="p">]</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to `{ y = 2; }`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-replaceStrings">
|
||
<a href="#builtins-replaceStrings"><code>replaceStrings <var>from</var> <var>to</var> <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Given string *s*, replace every occurrence of the strings in *from*
|
||
with the corresponding string in *to*.
|
||
|
||
The argument *to* is lazy, that is, it is only evaluated when its corresponding pattern in *from* is matched in the string *s*
|
||
|
||
Example:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>replaceStrings <span class="p">[</span><span class="s2">"oo"</span> <span class="s2">"a"</span><span class="p">]</span> <span class="p">[</span><span class="s2">"a"</span> <span class="s2">"i"</span><span class="p">]</span> <span class="s2">"foobar"</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to `"fabir"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-seq">
|
||
<a href="#builtins-seq"><code>seq <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Evaluate *e1*, then evaluate and return *e2*. This ensures that a
|
||
computation is strict in the value of *e1*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-sort">
|
||
<a href="#builtins-sort"><code>sort <var>comparator</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return *list* in sorted order. It repeatedly calls the function
|
||
*comparator* with two elements. The comparator should return `true`
|
||
if the first element is less than the second, and `false` otherwise.
|
||
For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>sort <span class="nb">builtins</span><span class="o">.</span>lessThan <span class="p">[</span> <span class="mi">483</span> <span class="mi">249</span> <span class="mi">526</span> <span class="mi">147</span> <span class="mi">42</span> <span class="mi">77</span> <span class="p">]</span>
|
||
</code></pre></div>
|
||
|
||
produces the list `[ 42 77 147 249 483 526 ]`.
|
||
|
||
This is a stable sort: it preserves the relative order of elements
|
||
deemed equal by the comparator.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-split">
|
||
<a href="#builtins-split"><code>split <var>regex</var> <var>str</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Returns a list composed of non matched strings interleaved with the
|
||
lists of the [extended POSIX regular
|
||
expression](http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04)
|
||
*regex* matches of *str*. Each item in the lists of matched
|
||
sequences is a regex group.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>split <span class="s2">"(a)b"</span> <span class="s2">"abc"</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `[ "" [ "a" ] "c" ]`.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>split <span class="s2">"([ac])"</span> <span class="s2">"abc"</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `[ "" [ "a" ] "b" [ "c" ] "" ]`.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>split <span class="s2">"(a)|(c)"</span> <span class="s2">"abc"</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `[ "" [ "a" null ] "b" [ null "c" ] "" ]`.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>split <span class="s2">"([[:upper:]]+)"</span> <span class="s2">" FOO "</span>
|
||
</code></pre></div>
|
||
|
||
Evaluates to `[ " " [ "FOO" ] " " ]`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-splitVersion">
|
||
<a href="#builtins-splitVersion"><code>splitVersion <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Split a string representing a version into its components, by the
|
||
same version splitting logic underlying the version comparison in
|
||
[`nix-env -u`](../Command-Reference/nix-env/index.md#operation---upgrade).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-storePath">
|
||
<a href="#builtins-storePath"><code>storePath <var>path</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
This function allows you to define a dependency on an already
|
||
existing store path. For example, the derivation attribute `src
|
||
= builtins.storePath /nix/store/f1d18v1y…-source` causes the
|
||
derivation to depend on the specified path, which must exist or
|
||
be substitutable. Note that this differs from a plain path
|
||
(e.g. `src = /nix/store/f1d18v1y…-source`) in that the latter
|
||
causes the path to be *copied* again to the Nix store, resulting
|
||
in a new path (e.g. `/nix/store/ld01dnzc…-source-source`).
|
||
|
||
Not available in [pure evaluation mode](../Command-Reference/conf-file.md#conf-pure-eval).
|
||
|
||
See also [`builtins.fetchClosure`](#builtins-fetchClosure).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-stringLength">
|
||
<a href="#builtins-stringLength"><code>stringLength <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the length of the string *e*. If *e* is not a string,
|
||
evaluation is aborted.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-sub">
|
||
<a href="#builtins-sub"><code>sub <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the difference between the numbers *e1* and *e2*.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-substring">
|
||
<a href="#builtins-substring"><code>substring <var>start</var> <var>len</var> <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the substring of *s* from character position *start*
|
||
(zero-based) up to but not including *start + len*. If *start* is
|
||
greater than the length of the string, an empty string is returned,
|
||
and if *start + len* lies beyond the end of the string, only the
|
||
substring up to the end of the string is returned. *start* must be
|
||
non-negative. For example,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>substring <span class="mi">0</span> <span class="mi">3</span> <span class="s2">"nixos"</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to `"nix"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-tail">
|
||
<a href="#builtins-tail"><code>tail <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return the second to last elements of a list; abort evaluation if
|
||
the argument isn’t a list or is an empty list.
|
||
|
||
!!! warning
|
||
>
|
||
> This function should generally be avoided since it's inefficient:
|
||
> unlike Haskell's `tail`, it takes O(n) time, so recursing over a
|
||
> list by repeatedly calling `tail` takes O(n^2) time.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-throw">
|
||
<a href="#builtins-throw"><code>throw <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Throw an error message *s*. This usually aborts Nix expression
|
||
evaluation, but in `nix-env -qa` and other commands that try to
|
||
evaluate a set of derivations to get information about those
|
||
derivations, a derivation that throws an error is silently skipped
|
||
(which is not the case for `abort`).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-toFile">
|
||
<a href="#builtins-toFile"><code>toFile <var>name</var> <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Store the string *s* in a file in the Nix store and return its
|
||
path. The file has suffix *name*. This file can be used as an
|
||
input to derivations. One application is to write builders
|
||
“inline”. For instance, the following Nix expression combines the
|
||
Nix expression for GNU Hello and its build script into one file:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">{</span> stdenv<span class="p">,</span> fetchurl<span class="p">,</span> perl <span class="p">}:</span>
|
||
|
||
stdenv<span class="o">.</span>mkDerivation <span class="p">{</span>
|
||
<span class="ss">name</span> <span class="o">=</span> <span class="s2">"hello-2.1.1"</span><span class="p">;</span>
|
||
|
||
<span class="ss">builder</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>toFile <span class="s2">"builder.sh"</span> <span class="s2">"</span>
|
||
<span class="s2"> source $stdenv/setup</span>
|
||
|
||
<span class="s2"> PATH=$perl/bin:$PATH</span>
|
||
|
||
<span class="s2"> tar xvfz $src</span>
|
||
<span class="s2"> cd hello-*</span>
|
||
<span class="s2"> ./configure --prefix=$out</span>
|
||
<span class="s2"> make</span>
|
||
<span class="s2"> make install</span>
|
||
<span class="s2"> "</span><span class="p">;</span>
|
||
|
||
<span class="ss">src</span> <span class="o">=</span> fetchurl <span class="p">{</span>
|
||
<span class="ss">url</span> <span class="o">=</span> <span class="s2">"http://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz"</span><span class="p">;</span>
|
||
<span class="ss">sha256</span> <span class="o">=</span> <span class="s2">"1md7jsfd8pa45z73bz1kszpp01yw6x5ljkjk2hx7wl800any6465"</span><span class="p">;</span>
|
||
<span class="p">};</span>
|
||
<span class="k">inherit</span> perl<span class="p">;</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
|
||
It is even possible for one file to refer to another, e.g.,
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="ss">builder</span> <span class="o">=</span> <span class="k">let</span>
|
||
<span class="ss">configFile</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>toFile <span class="s2">"foo.conf"</span> <span class="s2">"</span>
|
||
<span class="s2"> ## This is some dummy configuration file.</span>
|
||
<span class="s2"> ...</span>
|
||
<span class="s2"> "</span><span class="p">;</span>
|
||
<span class="k">in</span> <span class="nb">builtins</span><span class="o">.</span>toFile <span class="s2">"builder.sh"</span> <span class="s2">"</span>
|
||
<span class="s2"> source $stdenv/setup</span>
|
||
<span class="s2"> ...</span>
|
||
<span class="s2"> cp </span><span class="si">${</span>configFile<span class="si">}</span><span class="s2"> $out/etc/foo.conf</span>
|
||
<span class="s2">"</span><span class="p">;</span>
|
||
</code></pre></div>
|
||
|
||
Note that `${configFile}` is a
|
||
[string interpolation](../language/values.md#type-string), so the result of the
|
||
expression `configFile`
|
||
(i.e., a path like `/nix/store/m7p7jfny445k...-foo.conf`) will be
|
||
spliced into the resulting string.
|
||
|
||
It is however *not* allowed to have files mutually referring to each
|
||
other, like so:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="k">let</span>
|
||
<span class="ss">foo</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>toFile <span class="s2">"foo"</span> <span class="s2">"...</span><span class="si">${</span>bar<span class="si">}</span><span class="s2">..."</span><span class="p">;</span>
|
||
<span class="ss">bar</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>toFile <span class="s2">"bar"</span> <span class="s2">"...</span><span class="si">${</span>foo<span class="si">}</span><span class="s2">..."</span><span class="p">;</span>
|
||
<span class="k">in</span> foo
|
||
</code></pre></div>
|
||
|
||
This is not allowed because it would cause a cyclic dependency in
|
||
the computation of the cryptographic hashes for `foo` and `bar`.
|
||
|
||
It is also not possible to reference the result of a derivation. If
|
||
you are using Nixpkgs, the `writeTextFile` function is able to do
|
||
that.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-toJSON">
|
||
<a href="#builtins-toJSON"><code>toJSON <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a string containing a JSON representation of *e*. Strings,
|
||
integers, floats, booleans, nulls and lists are mapped to their JSON
|
||
equivalents. Sets (except derivations) are represented as objects.
|
||
Derivations are translated to a JSON string containing the
|
||
derivation’s output path. Paths are copied to the store and
|
||
represented as a JSON string of the resulting store path.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-toPath">
|
||
<a href="#builtins-toPath"><code>toPath <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
**DEPRECATED.** Use `/. + "/path"` to convert a string into an absolute
|
||
path. For relative paths, use `./. + "/path"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-toString">
|
||
<a href="#builtins-toString"><code>toString <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Convert the expression *e* to a string. *e* can be:
|
||
|
||
- A string (in which case the string is returned unmodified).
|
||
|
||
- A path (e.g., `toString /foo/bar` yields `"/foo/bar"`.
|
||
|
||
- A set containing `{ __toString = self: ...; }` or `{ outPath = ...; }`.
|
||
|
||
- An integer.
|
||
|
||
- A list, in which case the string representations of its elements
|
||
are joined with spaces.
|
||
|
||
- A Boolean (`false` yields `""`, `true` yields `"1"`).
|
||
|
||
- `null`, which yields the empty string.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-toXML">
|
||
<a href="#builtins-toXML"><code>toXML <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a string containing an XML representation of *e*. The main
|
||
application for `toXML` is to communicate information with the
|
||
builder in a more structured format than plain environment
|
||
variables.
|
||
|
||
Here is an example where this is the case:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="p">{</span> stdenv<span class="p">,</span> fetchurl<span class="p">,</span> libxslt<span class="p">,</span> jira<span class="p">,</span> uberwiki <span class="p">}:</span>
|
||
|
||
stdenv<span class="o">.</span>mkDerivation <span class="p">(</span><span class="k">rec</span> <span class="p">{</span>
|
||
<span class="ss">name</span> <span class="o">=</span> <span class="s2">"web-server"</span><span class="p">;</span>
|
||
|
||
<span class="ss">buildInputs</span> <span class="o">=</span> <span class="p">[</span> libxslt <span class="p">];</span>
|
||
|
||
<span class="ss">builder</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>toFile <span class="s2">"builder.sh"</span> <span class="s2">"</span>
|
||
<span class="s2"> source $stdenv/setup</span>
|
||
<span class="s2"> mkdir $out</span>
|
||
<span class="s2"> echo "</span><span class="err">$</span>servlets<span class="s2">" | xsltproc </span><span class="si">${</span>stylesheet<span class="si">}</span><span class="s2"> - > $out/server-conf.xml ①</span>
|
||
<span class="s2"> "</span><span class="p">;</span>
|
||
|
||
<span class="ss">stylesheet</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>toFile <span class="s2">"stylesheet.xsl"</span> <span class="err">②</span>
|
||
<span class="s2">"<?xml version='1.0' encoding='UTF-8'?></span>
|
||
<span class="s2"> <xsl:stylesheet xmlns:xsl='http://www.w3.org/1999/XSL/Transform' version='1.0'></span>
|
||
<span class="s2"> <xsl:template match='/'></span>
|
||
<span class="s2"> <Configure></span>
|
||
<span class="s2"> <xsl:for-each select='/expr/list/attrs'></span>
|
||
<span class="s2"> <Call name='addWebApplication'></span>
|
||
<span class="s2"> <Arg><xsl:value-of select="</span>attr<span class="p">[@</span><span class="ss">name</span> <span class="o">=</span> <span class="err">'</span>path'<span class="p">]</span><span class="l">/string</span><span class="o">/</span><span class="p">@</span>value<span class="s2">" /></Arg></span>
|
||
<span class="s2"> <Arg><xsl:value-of select="</span>attr<span class="p">[@</span><span class="ss">name</span> <span class="o">=</span> <span class="err">'</span>war'<span class="p">]</span><span class="l">/path</span><span class="o">/</span><span class="p">@</span>value<span class="s2">" /></Arg></span>
|
||
<span class="s2"> </Call></span>
|
||
<span class="s2"> </xsl:for-each></span>
|
||
<span class="s2"> </Configure></span>
|
||
<span class="s2"> </xsl:template></span>
|
||
<span class="s2"> </xsl:stylesheet></span>
|
||
<span class="s2"> "</span><span class="p">;</span>
|
||
|
||
<span class="ss">servlets</span> <span class="o">=</span> <span class="nb">builtins</span><span class="o">.</span>toXML <span class="p">[</span> <span class="err">③</span>
|
||
<span class="p">{</span> <span class="ss">path</span> <span class="o">=</span> <span class="s2">"/bugtracker"</span><span class="p">;</span> <span class="ss">war</span> <span class="o">=</span> jira <span class="o">+</span> <span class="s2">"/lib/atlassian-jira.war"</span><span class="p">;</span> <span class="p">}</span>
|
||
<span class="p">{</span> <span class="ss">path</span> <span class="o">=</span> <span class="s2">"/wiki"</span><span class="p">;</span> <span class="ss">war</span> <span class="o">=</span> uberwiki <span class="o">+</span> <span class="s2">"/uberwiki.war"</span><span class="p">;</span> <span class="p">}</span>
|
||
<span class="p">];</span>
|
||
<span class="p">})</span>
|
||
</code></pre></div>
|
||
|
||
The builder is supposed to generate the configuration file for a
|
||
[Jetty servlet container](http://jetty.mortbay.org/). A servlet
|
||
container contains a number of servlets (`*.war` files) each
|
||
exported under a specific URI prefix. So the servlet configuration
|
||
is a list of sets containing the `path` and `war` of the servlet
|
||
(①). This kind of information is difficult to communicate with the
|
||
normal method of passing information through an environment
|
||
variable, which just concatenates everything together into a
|
||
string (which might just work in this case, but wouldn’t work if
|
||
fields are optional or contain lists themselves). Instead the Nix
|
||
expression is converted to an XML representation with `toXML`,
|
||
which is unambiguous and can easily be processed with the
|
||
appropriate tools. For instance, in the example an XSLT stylesheet
|
||
(at point ②) is applied to it (at point ①) to generate the XML
|
||
configuration file for the Jetty server. The XML representation
|
||
produced at point ③ by `toXML` is as follows:
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="cp"><?xml version='1.0' encoding='utf-8'?></span>
|
||
<span class="nt"><expr></span>
|
||
<span class="w"> </span><span class="nt"><list></span>
|
||
<span class="w"> </span><span class="nt"><attrs></span>
|
||
<span class="w"> </span><span class="nt"><attr</span><span class="w"> </span><span class="na">name=</span><span class="s">"path"</span><span class="nt">></span>
|
||
<span class="w"> </span><span class="nt"><string</span><span class="w"> </span><span class="na">value=</span><span class="s">"/bugtracker"</span><span class="w"> </span><span class="nt">/></span>
|
||
<span class="w"> </span><span class="nt"></attr></span>
|
||
<span class="w"> </span><span class="nt"><attr</span><span class="w"> </span><span class="na">name=</span><span class="s">"war"</span><span class="nt">></span>
|
||
<span class="w"> </span><span class="nt"><path</span><span class="w"> </span><span class="na">value=</span><span class="s">"/nix/store/d1jh9pasa7k2...-jira/lib/atlassian-jira.war"</span><span class="w"> </span><span class="nt">/></span>
|
||
<span class="w"> </span><span class="nt"></attr></span>
|
||
<span class="w"> </span><span class="nt"></attrs></span>
|
||
<span class="w"> </span><span class="nt"><attrs></span>
|
||
<span class="w"> </span><span class="nt"><attr</span><span class="w"> </span><span class="na">name=</span><span class="s">"path"</span><span class="nt">></span>
|
||
<span class="w"> </span><span class="nt"><string</span><span class="w"> </span><span class="na">value=</span><span class="s">"/wiki"</span><span class="w"> </span><span class="nt">/></span>
|
||
<span class="w"> </span><span class="nt"></attr></span>
|
||
<span class="w"> </span><span class="nt"><attr</span><span class="w"> </span><span class="na">name=</span><span class="s">"war"</span><span class="nt">></span>
|
||
<span class="w"> </span><span class="nt"><path</span><span class="w"> </span><span class="na">value=</span><span class="s">"/nix/store/y6423b1yi4sx...-uberwiki/uberwiki.war"</span><span class="w"> </span><span class="nt">/></span>
|
||
<span class="w"> </span><span class="nt"></attr></span>
|
||
<span class="w"> </span><span class="nt"></attrs></span>
|
||
<span class="w"> </span><span class="nt"></list></span>
|
||
<span class="nt"></expr></span>
|
||
</code></pre></div>
|
||
|
||
Note that we used the `toFile` built-in to write the builder and
|
||
the stylesheet “inline” in the Nix expression. The path of the
|
||
stylesheet is spliced into the builder using the syntax `xsltproc
|
||
${stylesheet}`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-trace">
|
||
<a href="#builtins-trace"><code>trace <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Evaluate *e1* and print its abstract syntax representation on
|
||
standard error. Then return *e2*. This function is useful for
|
||
debugging.
|
||
|
||
If the
|
||
[`debugger-on-trace`](../Command-Reference/conf-file.md#conf-debugger-on-trace)
|
||
option is set to `true` and the `--debugger` flag is given, the
|
||
interactive debugger will be started when `trace` is called (like
|
||
[`break`](../language/builtins.md#builtins-break)).
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-traceVerbose">
|
||
<a href="#builtins-traceVerbose"><code>traceVerbose <var>e1</var> <var>e2</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Evaluate *e1* and print its abstract syntax representation on standard
|
||
error if `--trace-verbose` is enabled. Then return *e2*. This function
|
||
is useful for debugging.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-tryEval">
|
||
<a href="#builtins-tryEval"><code>tryEval <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Try to shallowly evaluate *e*. Return a set containing the
|
||
attributes `success` (`true` if *e* evaluated successfully,
|
||
`false` if an error was thrown) and `value`, equalling *e* if
|
||
successful and `false` otherwise. `tryEval` will only prevent
|
||
errors created by `throw` or `assert` from being thrown.
|
||
Errors `tryEval` will not catch are for example those created
|
||
by `abort` and type errors generated by builtins. Also note that
|
||
this doesn't evaluate *e* deeply, so `let e = { x = throw ""; };
|
||
in (builtins.tryEval e).success` will be `true`. Using
|
||
`builtins.deepSeq` one can get the expected result:
|
||
`let e = { x = throw ""; }; in
|
||
(builtins.tryEval (builtins.deepSeq e e)).success` will be
|
||
`false`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-typeOf">
|
||
<a href="#builtins-typeOf"><code>typeOf <var>e</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Return a string representing the type of the value *e*, namely
|
||
`"int"`, `"bool"`, `"string"`, `"path"`, `"null"`, `"set"`,
|
||
`"list"`, `"lambda"` or `"float"`.
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-unsafeDiscardOutputDependency">
|
||
<a href="#builtins-unsafeDiscardOutputDependency"><code>unsafeDiscardOutputDependency <var>s</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Create a copy of the given string where every "derivation deep" string context element is turned into a constant string context element.
|
||
|
||
This is the opposite of [`builtins.addDrvOutputDependencies`](#builtins-addDrvOutputDependencies).
|
||
|
||
This is unsafe because it allows us to "forget" store objects we would have otherwise refered to with the string context,
|
||
whereas Nix normally tracks all dependencies consistently.
|
||
Safe operations "grow" but never "shrink" string contexts.
|
||
[`builtins.addDrvOutputDependencies`] in contrast is safe because "derivation deep" string context element always refers to the underlying derivation (among many more things).
|
||
Replacing a constant string context element with a "derivation deep" element is a safe operation that just enlargens the string context without forgetting anything.
|
||
|
||
[`builtins.addDrvOutputDependencies`]: #builtins-addDrvOutputDependencies
|
||
|
||
</dd>
|
||
|
||
<dt id="builtins-zipAttrsWith">
|
||
<a href="#builtins-zipAttrsWith"><code>zipAttrsWith <var>f</var> <var>list</var></code></a>
|
||
</dt>
|
||
<dd>
|
||
|
||
Transpose a list of attribute sets into an attribute set of lists,
|
||
then apply `mapAttrs`.
|
||
|
||
`f` receives two arguments: the attribute name and a non-empty
|
||
list of all values encountered for that attribute name.
|
||
|
||
The result is an attribute set where the attribute names are the
|
||
union of the attribute names in each element of `list`. The attribute
|
||
values are the return values of `f`.
|
||
|
||
<div class="highlight"><pre><span></span><code><span class="nb">builtins</span><span class="o">.</span>zipAttrsWith
|
||
<span class="p">(</span>name<span class="p">:</span> values<span class="p">:</span> <span class="p">{</span> <span class="k">inherit</span> name values<span class="p">;</span> <span class="p">})</span>
|
||
<span class="p">[</span> <span class="p">{</span> <span class="ss">a</span> <span class="o">=</span> <span class="s2">"x"</span><span class="p">;</span> <span class="p">}</span> <span class="p">{</span> <span class="ss">a</span> <span class="o">=</span> <span class="s2">"y"</span><span class="p">;</span> <span class="ss">b</span> <span class="o">=</span> <span class="s2">"z"</span><span class="p">;</span> <span class="p">}</span> <span class="p">]</span>
|
||
</code></pre></div>
|
||
|
||
evaluates to
|
||
|
||
<div class="highlight"><pre><span></span><code>{
|
||
a = { name = "a"; values = [ "x" "y" ]; };
|
||
b = { name = "b"; values = [ "z" ]; };
|
||
}
|
||
</code></pre></div>
|
||
|
||
</dd>
|
||
|
||
|
||
</dl>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
</article>
|
||
</div>
|
||
|
||
|
||
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