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124 lines
4.2 KiB
XML
124 lines
4.2 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xml:id="sec-trivial-builders">
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<title>Trivial builders</title>
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<para>
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Nixpkgs provides a couple of functions that help with building
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derivations. The most important one,
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<function>stdenv.mkDerivation</function>, has already been
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documented above. The following functions wrap
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<function>stdenv.mkDerivation</function>, making it easier to use
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in certain cases.
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</para>
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<variablelist>
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<varlistentry>
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<term>
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<literal>runCommand</literal>
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</term>
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<listitem>
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<para>
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This takes three arguments, <literal>name</literal>,
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<literal>env</literal>, and <literal>buildCommand</literal>.
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<literal>name</literal> is just the name that Nix will append
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to the store path in the same way that
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<literal>stdenv.mkDerivation</literal> uses its
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<literal>name</literal> attribute. <literal>env</literal> is an
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attribute set specifying environment variables that will be set
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for this derivation. These attributes are then passed to the
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wrapped <literal>stdenv.mkDerivation</literal>.
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<literal>buildCommand</literal> specifies the commands that
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will be run to create this derivation. Note that you will need
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to create <literal>$out</literal> for Nix to register the
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command as successful.
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</para>
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<para>
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An example of using <literal>runCommand</literal> is provided
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below.
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</para>
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<programlisting>
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(import <nixpkgs> {}).runCommand "my-example" {} ''
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echo My example command is running
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mkdir $out
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echo I can write data to the Nix store > $out/message
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echo I can also run basic commands like:
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echo ls
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ls
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echo whoami
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whoami
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echo date
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date
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''
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</programlisting>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>runCommandCC</literal>
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</term>
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<listitem>
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<para>
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This works just like <literal>runCommand</literal>. The only
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difference is that it also provides a C compiler for your use.
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To minimize your dependencies, you should only use this if you
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are sure you will need a C compiler as part of running your command.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>writeTextFile</literal>, <literal>writeText</literal>,
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<literal>writeTextDir</literal>, <literal>writeScript</literal>,
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<literal>writeScriptBin</literal>
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</term>
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<listitem>
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<para>
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These functions write <literal>text</literal> to the Nix store.
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This is useful for creating scripts from Nix expressions.
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<literal>writeTextFile</literal> takes an attribute set and
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expects two arguments, <literal>name</literal> and
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<literal>text</literal>. <literal>name</literal> corresponds to
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the name used in the Nix store path. <literal>text</literal>
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will be the contents of the file. You can also set
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<literal>executable</literal> to true to make this file have
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the executable bit set.
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</para>
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<para>
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Many more commands wrap <literal>writeTextFile</literal>
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including <literal>writeText</literal>,
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<literal>writeTextDir</literal>,
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<literal>writeScript</literal>, and
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<literal>writeScriptBin</literal>. These are convenience
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functions over <literal>writeTextFile</literal>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>symlinkJoin</literal>
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</term>
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<listitem>
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<para>
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This can be used to put many derivations into the same directory
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structure. It works by creating a new derivation and adding
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symlinks to each of the paths listed. It expects two arguments,
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<literal>name</literal>, and <literal>paths</literal>.
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<literal>name</literal> is the name used in the Nix store path
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for the created derivation. <literal>paths</literal> is a list of
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paths that will be symlinked. These paths can be to Nix store
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derivations or any other subdirectory contained within.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</section>
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