Perl
Nixpkgs provides a function buildPerlPackage, a generic
package builder function for any Perl package that has a standard
Makefile.PL. It’s implemented in
pkgs/development/perl-modules/generic.
Perl packages from CPAN are defined in
pkgs/top-level/perl-packages.nix,
rather than pkgs/all-packages.nix. 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
perl-packages.nix. However, more complicated packages
should be put in a separate file, typically in
pkgs/development/perl-modules. Here is an example of the
former:
ClassC3 = buildPerlPackage rec {
name = "Class-C3-0.21";
src = fetchurl {
url = "mirror://cpan/authors/id/F/FL/FLORA/${name}.tar.gz";
sha256 = "1bl8z095y4js66pwxnm7s853pi9czala4sqc743fdlnk27kq94gz";
};
};
Note the use of mirror://cpan/, and the
${name} 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 all-packages.nix
through the variable perlPackages. For instance, if you
have a package that needs ClassC3, you would typically
write
foo = import ../path/to/foo.nix {
inherit stdenv fetchurl ...;
inherit (perlPackages) ClassC3;
};
in all-packages.nix. You can test building a Perl
package as follows:
$ nix-build -A perlPackages.ClassC3
buildPerlPackage adds perl- to the
start of the name attribute, so the package above is actually called
perl-Class-C3-0.21. So to install it, you can say:
$ nix-env -i perl-Class-C3
(Of course you can also install using the attribute name: nix-env -i
-A perlPackages.ClassC3.)
So what does buildPerlPackage do? It does the following:
In the configure phase, it calls perl Makefile.PL to
generate a Makefile. You can set the variable
makeMakerFlags to pass flags to
Makefile.PL
It adds the contents of the PERL5LIB environment variable
to #! .../bin/perl line of Perl scripts as
-Idir flags. This ensures
that a script can find its dependencies. (This can cause this shebang line
to become too long for Darwin to handle; see the note below.)
In the fixup phase, it writes the propagated build inputs
(propagatedBuildInputs) to the file
$out/nix-support/propagated-user-env-packages.
nix-env recursively installs all packages listed in
this file when you install a package that has it. This ensures that a Perl
package can find its dependencies.
buildPerlPackage is built on top of
stdenv, so everything can be customised in the usual way.
For instance, the BerkeleyDB module has a
preConfigure hook to generate a configuration file used by
Makefile.PL:
{ buildPerlPackage, fetchurl, db }:
buildPerlPackage rec {
name = "BerkeleyDB-0.36";
src = fetchurl {
url = "mirror://cpan/authors/id/P/PM/PMQS/${name}.tar.gz";
sha256 = "07xf50riarb60l1h6m2dqmql8q5dij619712fsgw7ach04d8g3z1";
};
preConfigure = ''
echo "LIB = ${db.out}/lib" > config.in
echo "INCLUDE = ${db.dev}/include" >> config.in
'';
}
Dependencies on other Perl packages can be specified in the
buildInputs and propagatedBuildInputs
attributes. If something is exclusively a build-time dependency, use
buildInputs; if it’s (also) a runtime dependency, use
propagatedBuildInputs. For instance, this builds a Perl
module that has runtime dependencies on a bunch of other modules:
ClassC3Componentised = buildPerlPackage rec {
name = "Class-C3-Componentised-1.0004";
src = fetchurl {
url = "mirror://cpan/authors/id/A/AS/ASH/${name}.tar.gz";
sha256 = "0xql73jkcdbq4q9m0b0rnca6nrlvf5hyzy8is0crdk65bynvs8q1";
};
propagatedBuildInputs = [
ClassC3 ClassInspector TestException MROCompat
];
};
On Darwin, if a script has too many
-Idir flags in its first line
(its “shebang line”), it will not run. This can be worked around by calling
the shortenPerlShebang function from the
postInstall phase:
{ stdenv, buildPerlPackage, fetchurl, shortenPerlShebang }:
ImageExifTool = buildPerlPackage {
pname = "Image-ExifTool";
version = "11.50";
src = fetchurl {
url = "https://www.sno.phy.queensu.ca/~phil/exiftool/Image-ExifTool-11.50.tar.gz";
sha256 = "0d8v48y94z8maxkmw1rv7v9m0jg2dc8xbp581njb6yhr7abwqdv3";
};
buildInputs = stdenv.lib.optional stdenv.isDarwin shortenPerlShebang;
postInstall = stdenv.lib.optional stdenv.isDarwin ''
shortenPerlShebang $out/bin/exiftool
'';
};
This will remove the -I flags from the shebang line,
rewrite them in the use lib 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.
Generation from CPAN
Nix expressions for Perl packages can be generated (almost) automatically
from CPAN. This is done by the program
nix-generate-from-cpan, which can be installed as
follows:
$ nix-env -i nix-generate-from-cpan
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:
$ nix-generate-from-cpan XML::Simple
XMLSimple = buildPerlPackage rec {
name = "XML-Simple-2.22";
src = fetchurl {
url = "mirror://cpan/authors/id/G/GR/GRANTM/${name}.tar.gz";
sha256 = "b9450ef22ea9644ae5d6ada086dc4300fa105be050a2030ebd4efd28c198eb49";
};
propagatedBuildInputs = [ XMLNamespaceSupport XMLSAX XMLSAXExpat ];
meta = {
description = "An API for simple XML files";
license = with stdenv.lib.licenses; [ artistic1 gpl1Plus ];
};
};
The output can be pasted into
pkgs/top-level/perl-packages.nix or wherever else you
need it.
Cross-compiling modules
Nixpkgs has experimental support for cross-compiling Perl modules. In many
cases, it will just work out of the box, even for modules with native
extensions. Sometimes, however, the Makefile.PL for a module may
(indirectly) import a native module. In that case, you will need to make a
stub for that module that will satisfy the Makefile.PL and install it into
lib/perl5/site_perl/cross_perl/${perl.version}. See the
postInstall for DBI for an example.