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359 lines
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359 lines
13 KiB
XML
<chapter 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 xml:id="opt-common">
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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> / <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>--quiet</option></term>
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<listitem>
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<para>Decreases the level of verbosity of diagnostic messages
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printed on standard error. This is the inverse option to
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<option>-v</option> / <option>--verbose</option>.
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</para>
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<para>This option may be specified repeatedly. See the previous
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verbosity levels list.</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><option>--no-build-output</option> / <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> / <option>-j</option>
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<replaceable>number</replaceable></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. Specify
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<literal>auto</literal> to use the number of CPUs in the system.
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The default is specified by the <link
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linkend='conf-max-jobs'><literal>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 xml:id="opt-cores"><term><option>--cores</option></term>
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<listitem><para>Sets the value of the <envar>NIX_BUILD_CORES</envar>
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environment variable in the invocation of builders. Builders can
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use this variable at their discretion to control the maximum amount
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of parallelism. For instance, in Nixpkgs, if the derivation
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attribute <varname>enableParallelBuilding</varname> is set to
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<literal>true</literal>, the builder passes the
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<option>-j<replaceable>N</replaceable></option> flag to GNU Make.
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It defaults to the value of the <link
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linkend='conf-cores'><literal>cores</literal></link>
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configuration setting, if set, or <literal>1</literal> otherwise.
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The value <literal>0</literal> means that the builder should use all
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available CPU cores in the system.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="opt-max-silent-time"><term><option>--max-silent-time</option></term>
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<listitem><para>Sets the maximum number of seconds that a builder
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can go without producing any data on standard output or standard
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error. The default is specified by the <link
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linkend='conf-max-silent-time'><literal>max-silent-time</literal></link>
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configuration setting. <literal>0</literal> means no
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time-out.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="opt-timeout"><term><option>--timeout</option></term>
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<listitem><para>Sets the maximum number of seconds that a builder
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can run. The default is specified by the <link
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linkend='conf-timeout'><literal>timeout</literal></link>
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configuration setting. <literal>0</literal> means no
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timeout.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--keep-going</option> / <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> / <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 installation 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>--no-build-hook</option></term>
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<listitem>
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<para>Disables the build hook mechanism. This allows to ignore remote
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builders if they are setup on the machine.</para>
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<para>It's useful in cases where the bandwidth between the client and the
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remote builder is too low. In that case it can take more time to upload the
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sources to the remote builder and fetch back the result than to do the
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computation locally.</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><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 top-level <literal>default.nix</literal> in
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Nixpkgs is 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 ? builtins.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>builtins.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><term><option>--argstr</option> <replaceable>name</replaceable> <replaceable>value</replaceable></term>
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<listitem><para>This option is like <option>--arg</option>, only the
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value is not a Nix expression but a string. So instead of
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<literal>--arg system \"i686-linux\"</literal> (the outer quotes are
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to keep the shell happy) you can say <literal>--argstr system
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i686-linux</literal>.</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>Select an attribute from the top-level Nix
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expression being evaluated. (<command>nix-env</command>,
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<command>nix-instantiate</command>, <command>nix-build</command> and
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<command>nix-shell</command> only.) 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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<varlistentry><term><option>--expr</option> / <option>-E</option></term>
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<listitem><para>Interpret the command line arguments as a list of
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Nix expressions to be parsed and evaluated, rather than as a list
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of file names of Nix expressions.
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(<command>nix-instantiate</command>, <command>nix-build</command>
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and <command>nix-shell</command> only.)</para></listitem>
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</varlistentry>
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<varlistentry xml:id="opt-I"><term><option>-I</option> <replaceable>path</replaceable></term>
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<listitem><para>Add a path to the Nix expression search path. This
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option may be given multiple times. See the <envar
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linkend="env-NIX_PATH">NIX_PATH</envar> environment variable for
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information on the semantics of the Nix search path. Paths added
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through <option>-I</option> take precedence over
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<envar>NIX_PATH</envar>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--option</option> <replaceable>name</replaceable> <replaceable>value</replaceable></term>
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<listitem><para>Set the Nix configuration option
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<replaceable>name</replaceable> to <replaceable>value</replaceable>.
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This overrides settings in the Nix configuration file (see
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<citerefentry><refentrytitle>nix.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--repair</option></term>
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<listitem><para>Fix corrupted or missing store paths by
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redownloading or rebuilding them. Note that this is slow because it
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requires computing a cryptographic hash of the contents of every
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path in the closure of the build. Also note the warning under
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<command>nix-store --repair-path</command>.</para></listitem>
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</varlistentry>
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</variablelist>
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</chapter>
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