Perl

Running a Perl script

Replacing #! with nix-shell

Perl scripts normally start something like this:

  #!/usr/bin/env perl

In Nix, we often make isolated environments using nix-shell. You can do this in the #! (shabang) section directly in the script too. Here is an example from the manual — a Perl script that specifies that it requires Perl and the HTML::TokeParser::Simple and LWP packages:

#! /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;
}

Invoking nix-shell on command-line

Can't locate DB_File.pm in @INC (you may need to install the DB_File module): run it with nix-shell -p perl -p perlPackages.DBFile --run ./myscript.pl

./myscript.pl: bad interpreter: /usr/bin/perl: no such file or directory: change the first line of the script to #!/usr/bin/env -S perl or start it with perl ./myscript.pl

Adding something from CPAN to nixpkgs

• Use the nix-generate-from-cpan.pl script (see nixpkgs/maintainers/scripts/) to generate something appropriate.
  Example usage: nix-generate-from-cpan.pl Devel::REPL
• After reviewing the result from the previous step and making appropriate modifications, add it to pkgs/top-level/perl-packages.nix. Note that some things use buildPerlPackage while some use buildPerlModule. Also note the mostly-followed naming convention as well as the mostly-followed alphabetical ordering. There are plenty of examples in perl-packages.nix — use the source, Luke!
• Build and test.

Wrappers for installed programs

To make perl modules available to a program in your derivation:

• add makeWrapper to nativeBuildInputs
• add

  postFixup = ''
    wrapProgram $out/bin/something \
      --prefix PERL5LIB : "${with perlPackages; makePerlPath [ something ]}"
  '';
  

See also

• Building a custom Perl package in NixOS