Document nix-shell #!-scripts

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Eelco Dolstra 2015-06-01 13:49:11 +02:00
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commit feca5cb67f

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@ -149,6 +149,15 @@ also <xref linkend="sec-common-options" />.</phrase></para>
</varlistentry> </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>
</variablelist> </variablelist>
<para>The following common options are supported:</para> <para>The following common options are supported:</para>
@ -203,6 +212,121 @@ $ nix-shell -p sqlite xorg.libX11
</refsection> </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>#1 /usr/bin/env nix-shell -i ...</literal> because
<command>/usr/bin/env</command> does not support passing options to
the interpreter.</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>Finally, the following Haskell script uses a specific branch of
Nixpkgs/NixOS (the 14.12 stable branch):
<programlisting><![CDATA[
#! /usr/bin/env nix-shell
#! nix-shell -i runghc -p haskellPackages.ghc haskellPackages.HTTP haskellPackages.tagsoup
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.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 &lt;nixpkgs> {};
runCommand "dummy" { buildInputs = [ python pythonPackages.prettytable ]; } ""
</programlisting>
</para>
</refsection>
<refsection condition="manpage"><title>Environment variables</title> <refsection condition="manpage"><title>Environment variables</title>
<variablelist> <variablelist>