Perl: Difference between revisions

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==Adding something from CPAN to nixpkgs==
==Adding something from CPAN to nixpkgs==


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


==Wrappers for installed programs==
==Wrappers for installed programs==


To make perl modules available to a program in your derivation:
To make perl modules available to a program in your derivation:
* add <code>makeWrapper</code> to <code>nativeBuildInputs</code>
# Add <code>makeWrapper</code> to <code>nativeBuildInputs</code>
* add <syntaxhighlight lang="nix">
# Add <syntaxhighlight lang="nix">
postFixup = ''
postFixup = ''
   wrapProgram $out/bin/something \
   wrapProgram $out/bin/something \

Revision as of 17:32, 27 September 2021

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

If you run a perl script and encounter a dependency error like this:

Can't locate DB_File.pm in @INC (you may need to install the DB_File module)

... use nix-shell to create a shell environment which includes the dependency. Here we searched NixOS packages and found an existing perl package which suits, like so.

nix-shell -p perl perl534Packages.DBFile --run ./myscript.pl

There is no /usr/bin/perl

By design, there is no /usr/bin/perl in Nix. So you may encounter messages like:

./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

  1. 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
    
  2. 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!
  3. Build and test.

Wrappers for installed programs

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

  1. Add makeWrapper to nativeBuildInputs
  2. Add
    postFixup = ''
      wrapProgram $out/bin/something \
        --prefix PERL5LIB : "${with perlPackages; makePerlPath [ something ]}"
    '';
    

See also