* Documented --attr / -A.
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@ -11,6 +11,13 @@
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<command>nix-build</command>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-common-syn.xml#xpointer(/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-drv-link</option></arg>
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<arg><option>--drv-link </option><replaceable>drvlink</replaceable></arg>
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<arg><option>--no-out-link</option></arg>
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@ -11,6 +11,13 @@
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<command>nix-env</command>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-common-syn.xml#xpointer(/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>
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<group choice='req'>
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<arg choice='plain'><option>--file</option></arg>
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@ -252,7 +259,7 @@ number of possible ways:
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</refsection>
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<refsection><title>Examples</title>
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<refsection xml:id='refsec-nix-env-install-examples'><title>Examples</title>
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<para>To install a specific version of <command>gcc</command> from the
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active Nix expression:
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@ -11,6 +11,13 @@
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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#xpointer(/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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<group choice='opt'>
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@ -224,8 +224,8 @@
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<command>nix-build</command>. When evaluating Nix expressions, the
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expression evaluator will automatically try to call functions that
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it encounters. It can automatically call functions for which every
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argument has a default value (e.g.,
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<literal>{<replaceable>argName</replaceable> ?
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argument has a <link linkend='ss-functions'>default value</link>
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(e.g., <literal>{<replaceable>argName</replaceable> ?
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<replaceable>defaultValue</replaceable>}:
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<replaceable>...</replaceable></literal>). With
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<option>--arg</option>, you can also call functions that have
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@ -257,6 +257,32 @@
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</varlistentry>
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<varlistentry xml:id="opt-attr"><term><option>--attr</option> / <option>-A</option>
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<replaceable>attrPath</replaceable></term>
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<listitem><para>In <command>nix-env</command>,
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<command>nix-instantiate</command> and <command>nix-build</command>,
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<option>--attr</option> allows you to select an attribute from the
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top-level Nix expression being evaluated. The <emphasis>attribute
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path</emphasis> <replaceable>attrPath</replaceable> is a sequence of
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attribute names separated by dots. For instance, given a top-level
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Nix expression <replaceable>e</replaceable>, the attribute path
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<literal>xorg.xorgserver</literal> would cause the expression
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<literal><replaceable>e</replaceable>.xorg.xorgserver</literal> to
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be used. See <link
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linkend='refsec-nix-env-install-examples'><command>nix-env
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--install</command></link> for some concrete examples.</para>
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<para>In addition to attribute names, you can also specify array
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indices. For instance, the attribute path
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<literal>foo.3.bar</literal> selects the <literal>bar</literal>
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attribute of the fourth element of the array in the
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<literal>foo</literal> attribute of the top-level
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expression.</para></listitem>
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</varlistentry>
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</variablelist>
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@ -428,7 +428,14 @@ lrwxrwxrwx ... 2006-09-29 10:43 result -> /nix/store/632d2b22514d...-hello-2.1.1
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$ ./result/bin/hello
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Hello, world!</screen>
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</para>
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The <link linkend='opt-attr'><option>-A</option></link> option selects
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the <literal>hello</literal> attribute from
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<filename>all-packages.nix</filename>. This is faster than using the
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symbolic package name specified by the <literal>name</literal>
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attribute (which also happens to be <literal>hello</literal>) and is
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unambiguous (there can be multiple packages with the symbolic name
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<literal>hello</literal>, but there can be only one attribute in a set
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named <literal>hello</literal>).</para>
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<para><command>nix-build</command> registers the
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<filename>./result</filename> symlink as a garbage collection root, so
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@ -470,8 +477,8 @@ So it is always safe to run multiple instances of Nix in parallel
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<para>If you have a system with multiple CPUs, you may want to have
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Nix build different derivations in parallel (insofar as possible).
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Just pass the option <option linkend='opt-max-jobs'>-j
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<replaceable>N</replaceable></option>, where
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Just pass the option <link linkend='opt-max-jobs'><option>-j
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<replaceable>N</replaceable></option></link>, where
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<replaceable>N</replaceable> is the maximum number of jobs to be run
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in parallel, or set. Typically this should be the number of
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CPUs.</para>
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