Change:
<del> <section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-language-perl"> <title>Perl</title> <section xml:id="ssec-perl-running"> <title>Running perl programs on the shell</title> <para> 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> to take the Perl installation from the <literal>PATH</literal> environment variable, or invoke Perl directly with: <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: <screen> <prompt>$ </prompt>nix-shell -p perl perlPackages.DBFile --run ./myscript.pl </screen> </para> <para> 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> </para> </section> <section xml:id="ssec-perl-packaging"> <title>Packaging Perl programs</title> <para> Nixpkgs provides a function <varname>buildPerlPackage</varname>, a generic package builder function for any Perl package that has a standard <varname>Makefile.PL</varname>. It’s implemented in <link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/perl-modules/generic"><filename>pkgs/development/perl-modules/generic</filename></link>. </para> <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: <programlisting> ClassC3 = buildPerlPackage rec { name = "Class-C3-0.21"; src = fetchurl { url = "mirror://cpan/authors/id/F/FL/FLORA/${name}.tar.gz"; sha256 = "1bl8z095y4js66pwxnm7s853pi9czala4sqc743fdlnk27kq94gz"; }; }; </programlisting> Note the use of <literal>mirror://cpan/</literal>, and the <literal>${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> in <filename>all-packages.nix</filename>. You can test building a Perl package as follows: <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> (Of course you can also install using the attribute name: <literal>nix-env -i -A perlPackages.ClassC3</literal>.) </para> <para> So what does <varname>buildPerlPackage</varname> do? It does the following: <orderedlist> <listitem> <para> In the configure phase, it calls <literal>perl Makefile.PL</literal> to generate a Makefile. You can set the variable <varname>makeMakerFlags</varname> to pass flags to <filename>Makefile.PL</filename> </para> </listitem> <listitem> <para> It adds the contents of the <envar>PERL5LIB</envar> environment variable to <literal>#! .../bin/perl</literal> line of Perl scripts as <literal>-I<replaceable>dir</replaceable></literal> 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.) </para> </listitem> <listitem> <para> In the fixup phase, it writes the propagated build inputs (<varname>propagatedBuildInputs</varname>) to the file <filename>$out/nix-support/propagated-user-env-packages</filename>. <command>nix-env</command> recursively installs all packages listed in this file when you install a package that has it. This ensures that a Perl package can find its dependencies. </para> </listitem> </orderedlist> </para> <para> <varname>buildPerlPackage</varname> is built on top of <varname>stdenv</varname>, so everything can be customised in the usual way. For instance, the <literal>BerkeleyDB</literal> module has a <varname>preConfigure</varname> hook to generate a configuration file used by <filename>Makefile.PL</filename>: <programlisting> { buildPerlPackage, fetchurl, db }: buildPerlPackage rec { name = "BerkeleyDB-0.36"; src = fetchurl { url = "mirror://cpan/authors/id/P/PM/PMQS/${name}.tar.gz"; sha256 = "07xf50riarb60l1h6m2dqmql8q5dij619712fsgw7ach04d8g3z1"; }; preConfigure = '' echo "LIB = ${db.out}/lib" > config.in echo "INCLUDE = ${db.dev}/include" >> config.in ''; } </programlisting> </para> <para> Dependencies on other Perl packages can be specified in the <varname>buildInputs</varname> and <varname>propagatedBuildInputs</varname> attributes. If something is exclusively a build-time dependency, use <varname>buildInputs</varname>; if it’s (also) a runtime dependency, use <varname>propagatedBuildInputs</varname>. For instance, this builds a Perl module that has runtime dependencies on a bunch of other modules: <programlisting> ClassC3Componentised = buildPerlPackage rec { name = "Class-C3-Componentised-1.0004"; src = fetchurl { url = "mirror://cpan/authors/id/A/AS/ASH/${name}.tar.gz"; sha256 = "0xql73jkcdbq4q9m0b0rnca6nrlvf5hyzy8is0crdk65bynvs8q1"; }; propagatedBuildInputs = [ ClassC3 ClassInspector TestException MROCompat ]; }; </programlisting> </para> <para> 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: <programlisting> { 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 $out/bin/exiftool ''; }; </programlisting> This will remove the <literal>-I</literal> flags from the shebang line, rewrite them in the <literal>use lib</literal> form, and put them on the next line instead. This function can be given any number of Perl scripts as arguments; it will modify them in-place. </para> <section xml:id="ssec-generation-from-CPAN"> <title>Generation from CPAN</title> <para> Nix expressions for Perl packages can be generated (almost) automatically from CPAN. This is done by the program <command>nix-generate-from-cpan</command>, which can be installed as follows: </para> <screen> <prompt>$ </prompt>nix-env -i nix-generate-from-cpan </screen> <para> 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: <screen> <prompt>$ </prompt>nix-generate-from-cpan XML::Simple XMLSimple = buildPerlPackage rec { name = "XML-Simple-2.22"; src = fetchurl { url = "mirror://cpan/authors/id/G/GR/GRANTM/${name}.tar.gz"; sha256 = "b9450ef22ea9644ae5d6ada086dc4300fa105be050a2030ebd4efd28c198eb49"; }; propagatedBuildInputs = [ XMLNamespaceSupport XMLSAX XMLSAXExpat ]; meta = { description = "An API for simple XML files"; license = with stdenv.lib.licenses; [ artistic1 gpl1Plus ]; }; }; </screen> The output can be pasted into <filename>pkgs/top-level/perl-packages.nix</filename> or wherever else you need it. </para> </section> <section xml:id="ssec-perl-cross-compilation"> <title>Cross-compiling modules</title> <para> Nixpkgs has experimental support for cross-compiling Perl modules. In many cases, it will just work out of the box, even for modules with native extensions. Sometimes, however, the Makefile.PL for a module may (indirectly) import a native module. In that case, you will need to make a stub for that module that will satisfy the Makefile.PL and install it into <filename>lib/perl5/site_perl/cross_perl/${perl.version}</filename>. See the <varname>postInstall</varname> for <varname>DBI</varname> for an example. </para> </section> </section> </section> </del>

Discussion:
This issue tracks the conversion of from Docbook to CommonMark per . If you intend to work on this conversion, please comment below! in this issue that you intend to work on it. (Please also post if you stop working on it) a new branch of nixpkgs master. : change to . to . the contents from Docbook to . Use existing sections for inspiration. from the folder to build the manual. the manual on your computer at after running from folder: it looks good, submit a PR and reference this issue.
Done. Works on my machine. Will send PR. Roast me.