When executing a Perl script, it is possible you get an error such as <literal>./myscript.pl: bad interpreter: /usr/bin/perl: no such file or directory</literal>. This happens when the script expects Perl to be installed at <filename>/usr/bin/perl</filename>, which is not the case when using Perl from nixpkgs. You can fix the script by changing the first line to:
<programlisting>
#!/usr/bin/env perl
</programlisting>
<programlisting>
#!/usr/bin/env perl
</programlisting>
to take the Perl installation from the <literal>PATH</literal> environment variable, or invoke Perl directly with:
<screen>
<prompt>$ </prompt>perl ./myscript.pl
</screen>
<screen>
<prompt>$ </prompt>perl ./myscript.pl
</screen>
</para>
<para>
When the script is using a Perl library that is not installed globally, you might get an error such as <literal>Can't locate DB_File.pm in @INC (you may need to install the DB_File module)</literal>. In that case, you can use <command>nix-shell</command> to start an ad-hoc shell with that library installed, for instance:
If you are always using the script in places where <command>nix-shell</command> is available, you can embed the <command>nix-shell</command> invocation in the shebang like this:
<programlisting>
#!/usr/bin/env nix-shell
#! nix-shell -i perl -p perl perlPackages.DBFile
</programlisting>
<programlisting>
#!/usr/bin/env nix-shell
#! nix-shell -i perl -p perl perlPackages.DBFile
</programlisting>
</para>
</section>
@@ -44,30 +44,30 @@
<para>
Perl packages from CPAN are defined in <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/perl-packages.nix"><filename>pkgs/top-level/perl-packages.nix</filename></link>, rather than <filename>pkgs/all-packages.nix</filename>. Most Perl packages are so straight-forward to build that they are defined here directly, rather than having a separate function for each package called from <filename>perl-packages.nix</filename>. However, more complicated packages should be put in a separate file, typically in <filename>pkgs/development/perl-modules</filename>. Here is an example of the former:
Note the use of <literal>mirror://cpan/</literal>, and the <literal>${name}</literal> in the URL definition to ensure that the name attribute is consistent with the source that we’re actually downloading. Perl packages are made available in <filename>all-packages.nix</filename> through the variable <varname>perlPackages</varname>. For instance, if you have a package that needs <varname>ClassC3</varname>, you would typically write
<programlisting>
foo = import ../path/to/foo.nix {
inherit stdenv fetchurl ...;
inherit (perlPackages) ClassC3;
};
</programlisting>
<programlisting>
foo = import ../path/to/foo.nix {
inherit stdenv fetchurl ...;
inherit (perlPackages) ClassC3;
};
</programlisting>
in <filename>all-packages.nix</filename>. You can test building a Perl package as follows:
<screen>
<prompt>$ </prompt>nix-build -A perlPackages.ClassC3
</screen>
<screen>
<prompt>$ </prompt>nix-build -A perlPackages.ClassC3
</screen>
<varname>buildPerlPackage</varname> adds <literal>perl-</literal> to the start of the name attribute, so the package above is actually called <literal>perl-Class-C3-0.21</literal>. So to install it, you can say:
<screen>
<prompt>$ </prompt>nix-env -i perl-Class-C3
</screen>
<screen>
<prompt>$ </prompt>nix-env -i perl-Class-C3
</screen>
(Of course you can also install using the attribute name: <literal>nix-env -i -A perlPackages.ClassC3</literal>.)
</para>
@@ -94,61 +94,61 @@
<para>
<varname>buildPerlPackage</varname> is built on top of <varname>stdenv</varname>, so everything can be customised in the usual way. For instance, the <literal>BerkeleyDB</literal> module has a <varname>preConfigure</varname> hook to generate a configuration file used by <filename>Makefile.PL</filename>:
Dependencies on other Perl packages can be specified in the <varname>buildInputs</varname> and <varname>propagatedBuildInputs</varname> attributes. If something is exclusively a build-time dependency, use <varname>buildInputs</varname>; if it’s (also) a runtime dependency, use <varname>propagatedBuildInputs</varname>. For instance, this builds a Perl module that has runtime dependencies on a bunch of other modules:
On Darwin, if a script has too many <literal>-I<replaceable>dir</replaceable></literal> flags in its first line (its “shebang line”), it will not run. This can be worked around by calling the <literal>shortenPerlShebang</literal> function from the <literal>postInstall</literal> phase:
This will remove the <literal>-I</literal> flags from the shebang line, rewrite them in the <literal>use lib</literal> form, and put them on the next line instead. This function can be given any number of Perl scripts as arguments; it will modify them in-place.
</para>
@@ -159,27 +159,27 @@
Nix expressions for Perl packages can be generated (almost) automatically from CPAN. This is done by the program <command>nix-generate-from-cpan</command>, which can be installed as follows:
This program takes a Perl module name, looks it up on CPAN, fetches and unpacks the corresponding package, and prints a Nix expression on standard output. For example:
For tools written in Ruby - i.e. where the desire is to install a package and then execute e.g. <command>rake</command> at the command line, there is an alternative builder called <literal>bundlerApp</literal>. Set up the <filename>gemset.nix</filename> the same way, and then, for example:
</para>
<screen>
<programlisting>
<![CDATA[{ lib, bundlerApp }:
bundlerApp {
@@ -75,7 +74,7 @@ bundlerApp {
platforms = platforms.unix;
};
}]]>
</screen>
</programlisting>
<para>
The chief advantage of <literal>bundlerApp</literal> over <literal>bundlerEnv</literal> is the executables introduced in the environment are precisely those selected in the <literal>exes</literal> list, as opposed to <literal>bundlerEnv</literal> which adds all the executables made available by gems in the gemset, which can mean e.g. <command>rspec</command> or <command>rake</command> in unpredictable versions available from various packages.
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Jan Tojnar