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290 lines
9.9 KiB
XML
290 lines
9.9 KiB
XML
<section xmlns="http://docbook.org/ns/docbook" xml:id="sec-common-options">
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<title>Common options</title>
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<para>Most Nix commands accept the following command-line options:</para>
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<variablelist>
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<varlistentry><term><option>--help</option></term>
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<listitem><para>Prints out a summary of the command syntax and
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exits.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--version</option></term>
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<listitem><para>Prints out the Nix version number on standard output
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and exits.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--verbose</option></term>
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<term><option>-v</option></term>
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<listitem>
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<para>Increases the level of verbosity of diagnostic messages
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printed on standard error. For each Nix operation, the information
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printed on standard output is well-defined; any diagnostic
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information is printed on standard error, never on standard
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output.</para>
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<para>This option may be specified repeatedly. Currently, the
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following verbosity levels exist:</para>
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<variablelist>
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<varlistentry><term>0</term>
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<listitem><para>“Errors only”: only print messages
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explaining why the Nix invocation failed.</para></listitem>
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</varlistentry>
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<varlistentry><term>1</term>
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<listitem><para>“Informational”: print
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<emphasis>useful</emphasis> messages about what Nix is doing.
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This is the default.</para></listitem>
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</varlistentry>
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<varlistentry><term>2</term>
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<listitem><para>“Talkative”: print more informational
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messages.</para></listitem>
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</varlistentry>
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<varlistentry><term>3</term>
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<listitem><para>“Chatty”: print even more
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informational messages.</para></listitem>
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</varlistentry>
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<varlistentry><term>4</term>
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<listitem><para>“Debug”: print debug
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information.</para></listitem>
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</varlistentry>
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<varlistentry><term>5</term>
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<listitem><para>“Vomit”: print vast amounts of debug
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information.</para></listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry><term><option>--no-build-output</option></term>
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<term><option>-Q</option></term>
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<listitem><para>By default, output written by builders to standard
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output and standard error is echoed to the Nix command's standard
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error. This option suppresses this behaviour. Note that the
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builder's standard output and error are always written to a log file
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in
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<filename><replaceable>prefix</replaceable>/nix/var/log/nix</filename>.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="opt-max-jobs"><term><option>--max-jobs</option></term>
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<term><option>-j</option></term>
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<listitem><para>Sets the maximum number of build jobs that Nix will
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perform in parallel to the specified number. The default is
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specified by the <link
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linkend='conf-build-max-jobs'><literal>build-max-jobs</literal></link>
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configuration setting, which itself defaults to
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<literal>1</literal>. A higher value is useful on SMP systems or to
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exploit I/O latency. </para></listitem>
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</varlistentry>
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<varlistentry><term><option>--keep-going</option></term>
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<term><option>-k</option></term>
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<listitem><para>Keep going in case of failed builds, to the
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greatest extent possible. That is, if building an input of some
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derivation fails, Nix will still build the other inputs, but not the
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derivation itself. Without this option, Nix stops if any build
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fails (except for builds of substitutes), possibly killing builds in
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progress (in case of parallel or distributed builds).</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--keep-failed</option></term>
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<term><option>-K</option></term>
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<listitem><para>Specifies that in case of a build failure, the
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temporary directory (usually in <filename>/tmp</filename>) in which
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the build takes place should not be deleted. The path of the build
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directory is printed as an informational message.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><option>--fallback</option></term>
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<listitem>
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<para>Whenever Nix attempts to build a derivation for which
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substitutes are known for each output path, but realising the output
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paths through the substitutes fails, fall back on building the
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derivation.</para>
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<para>The most common scenario in which this is useful is when we
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have registered substitutes in order to perform binary distribution
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from, say, a network repository. If the repository is down, the
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realisation of the derivation will fail. When this option is
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specified, Nix will build the derivation instead. Thus,
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installation from binaries falls back on nstallation from source.
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This option is not the default since it is generally not desirable
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for a transient failure in obtaining the substitutes to lead to a
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full build from source (with the related consumption of
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resources).</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><option>--readonly-mode</option></term>
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<listitem><para>When this option is used, no attempt is made to open
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the Nix database. Most Nix operations do need database access, so
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those operations will fail.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="opt-log-type"><term><option>--log-type</option>
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<replaceable>type</replaceable></term>
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<listitem>
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<para>This option determines how the output written to standard
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error is formatted. Nix’s diagnostic messages are typically
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<emphasis>nested</emphasis>. For instance, when tracing Nix
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expression evaluation (<command>nix-env -vvvvv</command>, messages
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from subexpressions are nested inside their parent expressions. Nix
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builder output is also often nested. For instance, the Nix Packages
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generic builder nests the various build tasks (unpack, configure,
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compile, etc.), and the GNU Make in <literal>stdenv-linux</literal>
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has been patched to provide nesting for recursive Make
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invocations.</para>
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<para><replaceable>type</replaceable> can be one of the
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following:
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<variablelist>
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<varlistentry><term><literal>pretty</literal></term>
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<listitem><para>Pretty-print the output, indicating different
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nesting levels using spaces. This is the
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default.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>escapes</literal></term>
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<listitem><para>Indicate nesting using escape codes that can be
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interpreted by the <command>nix-log2xml</command> tool in the
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Nix source distribution. The resulting XML file can be fed into
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the <command>log2html.xsl</command> stylesheet to create an HTML
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file that can be browsed interactively, using Javascript to
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expand and collapse parts of the output.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>flat</literal></term>
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<listitem><para>Remove all nesting.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><option>--arg</option> <replaceable>name</replaceable> <replaceable>value</replaceable></term>
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<listitem><para>This option is accepted by
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<command>nix-env</command>, <command>nix-instantiate</command> and
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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 <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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arguments without a default value (or override a default value).
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That is, if the evaluator encounters a function with an argument
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named <replaceable>name</replaceable>, it will call it with value
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<replaceable>value</replaceable>.</para>
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<para>For instance, the file
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<literal>pkgs/top-level/all-packages.nix</literal> in Nixpkgs is
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actually a function:
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<programlisting>
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{ # The system (e.g., `i686-linux') for which to build the packages.
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system ? __currentSystem
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<replaceable>...</replaceable>
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}: <replaceable>...</replaceable></programlisting>
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So if you call this Nix expression (e.g., when you do
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<literal>nix-env -i <replaceable>pkgname</replaceable></literal>),
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the function will be called automatically using the value <link
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linkend='builtin-currentSystem'><literal>__currentSystem</literal></link>
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for the <literal>system</literal> argument. You can override this
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using <option>--arg</option>, e.g., <literal>nix-env -i
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<replaceable>pkgname</replaceable> --arg system
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\"i686-freebsd\"</literal>. (Note that since the argument is a Nix
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string literal, you have to escape the quotes.)</para></listitem>
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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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</section>
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