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https://github.com/NixOS/nix.git
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202 lines
6.2 KiB
XML
202 lines
6.2 KiB
XML
<refentry 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-nix-instantiate">
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<refmeta>
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<refentrytitle>nix-instantiate</refentrytitle>
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<manvolnum>1</manvolnum>
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<refmiscinfo class="source">Nix</refmiscinfo>
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<refmiscinfo class="version"><xi:include href="version.txt" parse="text"/></refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>nix-instantiate</refname>
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<refpurpose>instantiate store derivations from Nix expressions</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>nix-instantiate</command>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-common-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
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<arg><option>--arg</option> <replaceable>name</replaceable> <replaceable>value</replaceable></arg>
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--attr</option></arg>
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<arg choice='plain'><option>-A</option></arg>
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</group>
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<replaceable>attrPath</replaceable>
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</arg>
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<arg><option>--add-root</option> <replaceable>path</replaceable></arg>
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<arg><option>--indirect</option></arg>
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<arg>
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<group choice='req'>
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<arg choice='plain'><option>--parse-only</option></arg>
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<arg choice='plain'>
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<option>--eval-only</option>
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<arg><option>--strict</option></arg>
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</arg>
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</group>
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<arg><option>--xml</option></arg>
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</arg>
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<arg choice='plain' rep='repeat'><replaceable>files</replaceable></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsection><title>Description</title>
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<para>The command <command>nix-instantiate</command> generates <link
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linkend="gloss-derivation">store derivations</link> from (high-level)
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Nix expressions. It loads and evaluates the Nix expressions in each
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of <replaceable>files</replaceable>. Each top-level expression should
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evaluate to a derivation, a list of derivations, or a set of
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derivations. The paths of the resulting store derivations are printed
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on standard output.</para>
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<para>If <replaceable>files</replaceable> is the character
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<literal>-</literal>, then a Nix expression will be read from standard
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input.</para>
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<para>Most users and developers don’t need to use this command
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(<command>nix-env</command> and <command>nix-build</command> perform
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store derivation instantiation from Nix expressions automatically).
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It is most commonly used for implementing new deployment
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policies.</para>
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<para>See also <xref linkend="sec-common-options" /> for a list of
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common options.</para>
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</refsection>
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<refsection><title>Options</title>
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<variablelist>
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<varlistentry>
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<term><option>--add-root</option> <replaceable>path</replaceable></term>
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<term><option>--indirect</option></term>
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<listitem><para>See the <link linkend="opt-add-root">corresponding
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options</link> in <command>nix-store</command>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--parse-only</option></term>
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<listitem><para>Just parse the input files, and print their
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abstract syntax trees on standard output in ATerm
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format.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--eval-only</option></term>
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<listitem><para>Just parse and evaluate the input files, and print
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the resulting values on standard output. No instantiation of
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store derivations takes place.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--xml</option></term>
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<listitem><para>When used with <option>--parse-only</option> and
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<option>--eval-only</option>, print the resulting expression as an
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XML representation of the abstract syntax tree rather than as an
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ATerm. The schema is the same as that used by the <link
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linkend="builtin-toXML"><function>toXML</function>
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built-in</link>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--strict</option></term>
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<listitem><para>When used with <option>--eval-only</option>,
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recursively evaluate list elements and attributes. Normally, such
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sub-expressions are left unevaluated (since the Nix expression
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language is lazy).</para>
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<warning><para>This option can cause non-termination, because lazy
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data structures can be infinitely large.</para></warning>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsection>
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<refsection><title>Examples</title>
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<para>Instantiating store derivations from a Nix expression, and
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building them using <command>nix-store</command>:
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<screen>
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$ nix-instantiate test.nix <lineannotation>(instantiate)</lineannotation>
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/nix/store/cigxbmvy6dzix98dxxh9b6shg7ar5bvs-perl-BerkeleyDB-0.26.drv
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$ nix-store -r $(nix-instantiate test.nix) <lineannotation>(build)</lineannotation>
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<replaceable>...</replaceable>
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/nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26 <lineannotation>(output path)</lineannotation>
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$ ls -l /nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26
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dr-xr-xr-x 2 eelco users 4096 1970-01-01 01:00 lib
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...</screen>
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</para>
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<para>Parsing and evaluating Nix expressions:
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<screen>
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$ echo '"foo" + "bar"' | nix-instantiate --parse-only -
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OpPlus(Str("foo"),Str("bar"))
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$ echo '"foo" + "bar"' | nix-instantiate --eval-only -
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Str("foobar")
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$ echo '"foo" + "bar"' | nix-instantiate --eval-only --xml -
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<![CDATA[<?xml version='1.0' encoding='utf-8'?>
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<expr>
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<string value="foobar" />
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</expr>]]></screen>
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</para>
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<para>The difference between non-strict and strict evaluation:
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<screen>
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$ echo 'rec { x = "foo"; y = x; }' | nix-instantiate --eval-only --xml -
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<replaceable>...</replaceable><![CDATA[
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<attr name="x">
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<string value="foo" />
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</attr>
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<attr name="y">
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<unevaluated />
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</attr>]]>
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<replaceable>...</replaceable></screen>
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Note that <varname>y</varname> is left unevaluated (the XML
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representation doesn’t attempt to show non-normal forms).
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<screen>
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$ echo 'rec { x = "foo"; y = x; }' | nix-instantiate --eval-only --xml --strict -
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<replaceable>...</replaceable><![CDATA[
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<attr name="x">
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<string value="foo" />
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</attr>
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<attr name="y">
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<string value="foo" />
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</attr>]]>
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<replaceable>...</replaceable></screen>
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</para>
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</refsection>
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</refentry>
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