about summary refs log tree commit diff
path: root/doc/manual/nix-instantiate.xml
blob: 618b61f159dcad14620d6bad20c1d09ca3aa86fc (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
<refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          xml:id="sec-nix-instantiate">
  
<refmeta>
  <refentrytitle>nix-instantiate</refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo class="source">Nix</refmiscinfo>
  <refmiscinfo class="version"><xi:include href="version.txt" parse="text"/></refmiscinfo>
</refmeta>

<refnamediv>
  <refname>nix-instantiate</refname>
  <refpurpose>instantiate store derivations from Nix expressions</refpurpose>
</refnamediv>

<refsynopsisdiv>
  <cmdsynopsis>
    <command>nix-instantiate</command>
    <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/*)" />
    <arg><option>--arg</option> <replaceable>name</replaceable> <replaceable>value</replaceable></arg>
    <arg>
      <group choice='req'>
        <arg choice='plain'><option>--attr</option></arg>
        <arg choice='plain'><option>-A</option></arg>
      </group>
      <replaceable>attrPath</replaceable>
    </arg>
    <arg><option>--add-root</option> <replaceable>path</replaceable></arg>
    <arg><option>--indirect</option></arg>
    <arg>
      <group choice='req'>
        <arg choice='plain'><option>--parse-only</option></arg>
        <arg choice='plain'>
          <option>--eval-only</option>
          <arg><option>--strict</option></arg>
        </arg>
        <arg choice='plain'><option>--find-file</option></arg>
      </group>
      <arg><option>--xml</option></arg>
    </arg>
    <arg choice='plain' rep='repeat'><replaceable>files</replaceable></arg>
  </cmdsynopsis>
</refsynopsisdiv>


<refsection><title>Description</title>

<para>The command <command>nix-instantiate</command> generates <link
linkend="gloss-derivation">store derivations</link> from (high-level)
Nix expressions.  It loads and evaluates the Nix expressions in each
of <replaceable>files</replaceable> (which defaults to
<replaceable>./default.nix</replaceable>).  Each top-level expression
should evaluate to a derivation, a list of derivations, or a set of
derivations.  The paths of the resulting store derivations are printed
on standard output.</para>

<para>If <replaceable>files</replaceable> is the character
<literal>-</literal>, then a Nix expression will be read from standard
input.</para>

<para>Most users and developers don’t need to use this command
(<command>nix-env</command> and <command>nix-build</command> perform
store derivation instantiation from Nix expressions automatically).
It is most commonly used for implementing new deployment
policies.</para>

<para condition="manual">See also <xref linkend="sec-common-options"
/> for a list of common options.</para>

</refsection>


<refsection><title>Options</title>

<variablelist>

  <varlistentry>
    <term><option>--add-root</option> <replaceable>path</replaceable></term>
    <term><option>--indirect</option></term>

    <listitem><para>See the <link linkend="opt-add-root">corresponding
    options</link> in <command>nix-store</command>.</para></listitem>

  </varlistentry>

    
  <varlistentry><term><option>--parse-only</option></term>
  
    <listitem><para>Just parse the input files, and print their
    abstract syntax trees on standard output in ATerm
    format.</para></listitem>
    
  </varlistentry>
      
  <varlistentry><term><option>--eval-only</option></term>
  
    <listitem><para>Just parse and evaluate the input files, and print
    the resulting values on standard output.  No instantiation of
    store derivations takes place.</para></listitem>
    
  </varlistentry>

  <varlistentry><term><option>--find-file</option></term>
  
    <listitem><para>Look up the given files in Nix’s search path (as
    specified by the <envar>NIX_PATH</envar> environment variable).
    If found, print the corresponding absolute paths on standard
    output.  For instance, if <envar>NIX_PATH</envar> is
    <literal>nixpkgs=/home/alice/nixpkgs</literal>, then
    <literal>nix-instantiate --find-file nixpkgs/default.nix</literal>
    will print
    <literal>/home/alice/nixpkgs/default.nix</literal>.</para></listitem>
    
  </varlistentry>
      
  <varlistentry><term><option>--xml</option></term>

    <listitem><para>When used with <option>--parse-only</option> and
    <option>--eval-only</option>, print the resulting expression as an
    XML representation of the abstract syntax tree rather than as an
    ATerm.  The schema is the same as that used by the <link
    linkend="builtin-toXML"><function>toXML</function>
    built-in</link>.</para></listitem>

  </varlistentry>

  <varlistentry><term><option>--strict</option></term>

    <listitem><para>When used with <option>--eval-only</option>,
    recursively evaluate list elements and attributes.  Normally, such
    sub-expressions are left unevaluated (since the Nix expression
    language is lazy).</para>

    <warning><para>This option can cause non-termination, because lazy
    data structures can be infinitely large.</para></warning>

    </listitem>

  </varlistentry>

</variablelist>

<variablelist condition="manpage">
  <xi:include href="opt-common.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(//db:variablelist[@xml:id='opt-common']/*)" />
</variablelist>

</refsection>


<refsection><title>Examples</title>

<para>Instantiating store derivations from a Nix expression, and
building them using <command>nix-store</command>:

<screen>
$ nix-instantiate test.nix <lineannotation>(instantiate)</lineannotation>
/nix/store/cigxbmvy6dzix98dxxh9b6shg7ar5bvs-perl-BerkeleyDB-0.26.drv

$ nix-store -r $(nix-instantiate test.nix) <lineannotation>(build)</lineannotation>
<replaceable>...</replaceable>
/nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26 <lineannotation>(output path)</lineannotation>

$ ls -l /nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26
dr-xr-xr-x    2 eelco    users        4096 1970-01-01 01:00 lib
...</screen>

</para>

<para>Parsing and evaluating Nix expressions:

<screen>
$ echo '"foo" + "bar"' | nix-instantiate --parse-only -
OpPlus(Str("foo"),Str("bar"))

$ echo '"foo" + "bar"' | nix-instantiate --eval-only -
Str("foobar")

$ echo '"foo" + "bar"' | nix-instantiate --eval-only --xml -
<![CDATA[<?xml version='1.0' encoding='utf-8'?>
<expr>
  <string value="foobar" />
</expr>]]></screen>

</para>

<para>The difference between non-strict and strict evaluation:

<screen>
$ echo 'rec { x = "foo"; y = x; }' | nix-instantiate --eval-only --xml -
<replaceable>...</replaceable><![CDATA[
    <attr name="x">
      <string value="foo" />
    </attr>
    <attr name="y">
      <unevaluated />
    </attr>]]>
<replaceable>...</replaceable></screen>

Note that <varname>y</varname> is left unevaluated (the XML
representation doesn’t attempt to show non-normal forms).

<screen>
$ echo 'rec { x = "foo"; y = x; }' | nix-instantiate --eval-only --xml --strict -
<replaceable>...</replaceable><![CDATA[
    <attr name="x">
      <string value="foo" />
    </attr>
    <attr name="y">
      <string value="foo" />
    </attr>]]>
<replaceable>...</replaceable></screen>

</para>

</refsection>


<refsection condition="manpage"><title>Environment variables</title>

<variablelist>
  <xi:include href="env-common.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(//db:variablelist[@xml:id='env-common']/*)" />
</variablelist>

</refsection>
  

</refentry>