<refentry xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude" version="5.0" xml:id="sec-nix-shell"> <refmeta> <refentrytitle>nix-shell</refentrytitle> <manvolnum>1</manvolnum> <refmiscinfo class="source">Nix</refmiscinfo> <refmiscinfo class="version"><xi:include href="../version.txt" parse="text"/></refmiscinfo> </refmeta> <refnamediv> <refname>nix-shell</refname> <refpurpose>start an interactive shell based on a Nix expression</refpurpose> </refnamediv> <refsynopsisdiv> <cmdsynopsis> <command>nix-shell</command> <arg><option>--arg</option> <replaceable>name</replaceable> <replaceable>value</replaceable></arg> <arg><option>--argstr</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>--command</option> <replaceable>cmd</replaceable></arg> <arg><option>--run</option> <replaceable>cmd</replaceable></arg> <arg><option>--exclude</option> <replaceable>regexp</replaceable></arg> <arg><option>--pure</option></arg> <arg><option>--keep</option> <replaceable>name</replaceable></arg> <group choice='req'> <arg choice='plain'> <group choice='req'> <arg choice='plain'><option>--packages</option></arg> <arg choice='plain'><option>-p</option></arg> </group> <arg choice='plain' rep='repeat'> <group choice='req'> <arg choice="plain"><replaceable>packages</replaceable></arg> <arg choice="plain"><replaceable>expressions</replaceable></arg> </group> </arg> </arg> <arg><replaceable>path</replaceable></arg> </group> </cmdsynopsis> </refsynopsisdiv> <refsection><title>Description</title> <para>The command <command>nix-shell</command> will build the dependencies of the specified derivation, but not the derivation itself. It will then start an interactive shell in which all environment variables defined by the derivation <replaceable>path</replaceable> have been set to their corresponding values, and the script <literal>$stdenv/setup</literal> has been sourced. This is useful for reproducing the environment of a derivation for development.</para> <para>If <replaceable>path</replaceable> is not given, <command>nix-shell</command> defaults to <filename>shell.nix</filename> if it exists, and <filename>default.nix</filename> otherwise.</para> <para>If <replaceable>path</replaceable> starts with <literal>http://</literal> or <literal>https://</literal>, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must include a single top-level directory containing at least a file named <filename>default.nix</filename>.</para> <para>If the derivation defines the variable <varname>shellHook</varname>, it will be evaluated after <literal>$stdenv/setup</literal> has been sourced. Since this hook is not executed by regular Nix builds, it allows you to perform initialisation specific to <command>nix-shell</command>. For example, the derivation attribute <programlisting> shellHook = '' echo "Hello shell" ''; </programlisting> will cause <command>nix-shell</command> to print <literal>Hello shell</literal>.</para> </refsection> <refsection><title>Options</title> <para>All options not listed here are passed to <command>nix-store --realise</command>, except for <option>--arg</option> and <option>--attr</option> / <option>-A</option> which are passed to <command>nix-instantiate</command>. <phrase condition="manual">See also <xref linkend="sec-common-options" />.</phrase></para> <variablelist> <varlistentry><term><option>--command</option> <replaceable>cmd</replaceable></term> <listitem><para>In the environment of the derivation, run the shell command <replaceable>cmd</replaceable>. This command is executed in an interactive shell. (Use <option>--run</option> to use a non-interactive shell instead.) However, a call to <literal>exit</literal> is implicitly added to the command, so the shell will exit after running the command. To prevent this, add <literal>return</literal> at the end; e.g. <literal>--command "echo Hello; return"</literal> will print <literal>Hello</literal> and then drop you into the interactive shell. This can be useful for doing any additional initialisation.</para></listitem> </varlistentry> <varlistentry><term><option>--run</option> <replaceable>cmd</replaceable></term> <listitem><para>Like <option>--command</option>, but executes the command in a non-interactive shell. This means (among other things) that if you hit Ctrl-C while the command is running, the shell exits.</para></listitem> </varlistentry> <varlistentry><term><option>--exclude</option> <replaceable>regexp</replaceable></term> <listitem><para>Do not build any dependencies whose store path matches the regular expression <replaceable>regexp</replaceable>. This option may be specified multiple times.</para></listitem> </varlistentry> <varlistentry><term><option>--pure</option></term> <listitem><para>If this flag is specified, the environment is almost entirely cleared before the interactive shell is started, so you get an environment that more closely corresponds to the “real” Nix build. A few variables, in particular <envar>HOME</envar>, <envar>USER</envar> and <envar>DISPLAY</envar>, are retained. Note that <filename>~/.bashrc</filename> and (depending on your Bash installation) <filename>/etc/bashrc</filename> are still sourced, so any variables set there will affect the interactive shell.</para></listitem> </varlistentry> <varlistentry><term><option>--packages</option> / <option>-p</option> <replaceable>packages</replaceable>…</term> <listitem><para>Set up an environment in which the specified packages are present. The command line arguments are interpreted as attribute names inside the Nix Packages collection. Thus, <literal>nix-shell -p libjpeg openjdk</literal> will start a shell in which the packages denoted by the attribute names <varname>libjpeg</varname> and <varname>openjdk</varname> are present.</para></listitem> </varlistentry> <varlistentry><term><option>-i</option> <replaceable>interpreter</replaceable></term> <listitem><para>The chained script interpreter to be invoked by <command>nix-shell</command>. Only applicable in <literal>#!</literal>-scripts (described <link linkend="ssec-nix-shell-shebang">below</link>).</para> </listitem></varlistentry> <varlistentry><term><option>--keep</option> <replaceable>name</replaceable></term> <listitem><para>When a <option>--pure</option> shell is started, keep the listed environment variables.</para></listitem> </varlistentry> </variablelist> <para>The following common options are supported:</para> <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>Environment variables</title> <variablelist> <varlistentry><term><envar>NIX_BUILD_SHELL</envar></term> <listitem><para>Shell used to start the interactive environment. Defaults to the <command>bash</command> found in <envar>PATH</envar>.</para></listitem> </varlistentry> </variablelist> </refsection> <refsection><title>Examples</title> <para>To build the dependencies of the package Pan, and start an interactive shell in which to build it: <screen> $ nix-shell '<nixpkgs>' -A pan [nix-shell]$ unpackPhase [nix-shell]$ cd pan-* [nix-shell]$ configurePhase [nix-shell]$ buildPhase [nix-shell]$ ./pan/gui/pan </screen> To clear the environment first, and do some additional automatic initialisation of the interactive shell: <screen> $ nix-shell '<nixpkgs>' -A pan --pure \ --command 'export NIX_DEBUG=1; export NIX_CORES=8; return' </screen> Nix expressions can also be given on the command line using the <command>-E</command> and <command>-p</command> flags. For instance, the following starts a shell containing the packages <literal>sqlite</literal> and <literal>libX11</literal>: <screen> $ nix-shell -E 'with import <nixpkgs> { }; runCommand "dummy" { buildInputs = [ sqlite xorg.libX11 ]; } ""' </screen> A shorter way to do the same is: <screen> $ nix-shell -p sqlite xorg.libX11 [nix-shell]$ echo $NIX_LDFLAGS … -L/nix/store/j1zg5v…-sqlite-3.8.0.2/lib -L/nix/store/0gmcz9…-libX11-1.6.1/lib … </screen> Note that <command>-p</command> accepts multiple full nix expressions that are valid in the <literal>buildInputs = [ ... ]</literal> shown above, not only package names. So the following is also legal: <screen> $ nix-shell -p sqlite 'git.override { withManual = false; }' </screen> The <command>-p</command> flag looks up Nixpkgs in the Nix search path. You can override it by passing <option>-I</option> or setting <envar>NIX_PATH</envar>. For example, the following gives you a shell containing the Pan package from a specific revision of Nixpkgs: <screen> $ nix-shell -p pan -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2.tar.gz [nix-shell:~]$ pan --version Pan 0.139 </screen> </para> </refsection> <refsection xml:id="ssec-nix-shell-shebang"><title>Use as a <literal>#!</literal>-interpreter</title> <para>You can use <command>nix-shell</command> as a script interpreter to allow scripts written in arbitrary languages to obtain their own dependencies via Nix. This is done by starting the script with the following lines: <programlisting> #! /usr/bin/env nix-shell #! nix-shell -i <replaceable>real-interpreter</replaceable> -p <replaceable>packages</replaceable> </programlisting> where <replaceable>real-interpreter</replaceable> is the “real” script interpreter that will be invoked by <command>nix-shell</command> after it has obtained the dependencies and initialised the environment, and <replaceable>packages</replaceable> are the attribute names of the dependencies in Nixpkgs.</para> <para>The lines starting with <literal>#! nix-shell</literal> specify <command>nix-shell</command> options (see above). Note that you cannot write <literal>#! /usr/bin/env nix-shell -i ...</literal> because many operating systems only allow one argument in <literal>#!</literal> lines.</para> <para>For example, here is a Python script that depends on Python and the <literal>prettytable</literal> package: <programlisting> #! /usr/bin/env nix-shell #! nix-shell -i python -p python pythonPackages.prettytable import prettytable # Print a simple table. t = prettytable.PrettyTable(["N", "N^2"]) for n in range(1, 10): t.add_row([n, n * n]) print t </programlisting> </para> <para>Similarly, the following is a Perl script that specifies that it requires Perl and the <literal>HTML::TokeParser::Simple</literal> and <literal>LWP</literal> packages: <programlisting> #! /usr/bin/env nix-shell #! nix-shell -i perl -p perl perlPackages.HTMLTokeParserSimple perlPackages.LWP use HTML::TokeParser::Simple; # Fetch nixos.org and print all hrefs. my $p = HTML::TokeParser::Simple->new(url => 'http://nixos.org/'); while (my $token = $p->get_tag("a")) { my $href = $token->get_attr("href"); print "$href\n" if $href; } </programlisting> </para> <para>Sometimes you need to pass a simple Nix expression to customize a package like Terraform: <programlisting><![CDATA[ #! /usr/bin/env nix-shell #! nix-shell -i bash -p "terraform.withPlugins (plugins: [ plugins.openstack ])" terraform apply ]]></programlisting> <note><para>You must use double quotes (<literal>"</literal>) when passing a simple Nix expression in a nix-shell shebang.</para></note> </para> <para>Finally, using the merging of multiple nix-shell shebangs the following Haskell script uses a specific branch of Nixpkgs/NixOS (the 18.03 stable branch): <programlisting><![CDATA[ #! /usr/bin/env nix-shell #! nix-shell -i runghc -p "haskellPackages.ghcWithPackages (ps: [ps.HTTP ps.tagsoup])" #! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.03.tar.gz import Network.HTTP import Text.HTML.TagSoup -- Fetch nixos.org and print all hrefs. main = do resp <- Network.HTTP.simpleHTTP (getRequest "http://nixos.org/") body <- getResponseBody resp let tags = filter (isTagOpenName "a") $ parseTags body let tags' = map (fromAttrib "href") tags mapM_ putStrLn $ filter (/= "") tags' ]]></programlisting> If you want to be even more precise, you can specify a specific revision of Nixpkgs: <programlisting> #! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/0672315759b3e15e2121365f067c1c8c56bb4722.tar.gz </programlisting> </para> <para>The examples above all used <option>-p</option> to get dependencies from Nixpkgs. You can also use a Nix expression to build your own dependencies. For example, the Python example could have been written as: <programlisting> #! /usr/bin/env nix-shell #! nix-shell deps.nix -i python </programlisting> where the file <filename>deps.nix</filename> in the same directory as the <literal>#!</literal>-script contains: <programlisting> with import <nixpkgs> {}; runCommand "dummy" { buildInputs = [ python pythonPackages.prettytable ]; } "" </programlisting> </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>