doc: Port Perl to Markdown

3 files changed, 164 insertions, 196 deletions

diff --git a/doc/languages-frameworks/index.xml b/doc/languages-frameworks/index.xml
index daa57cf1f86..0d016b660bd 100644
--- a/doc/languages-frameworks/index.xml
+++ b/doc/languages-frameworks/index.xml
@@ -22,7 +22,7 @@
  <xi:include href="maven.section.xml" />
  <xi:include href="node.section.xml" />
  <xi:include href="ocaml.section.xml" />
- <xi:include href="perl.xml" />
+ <xi:include href="perl.section.xml" />
  <xi:include href="php.section.xml" />
  <xi:include href="python.section.xml" />
  <xi:include href="qt.section.xml" />
diff --git a/doc/languages-frameworks/perl.section.md b/doc/languages-frameworks/perl.section.md
new file mode 100644
index 00000000000..2b31da84553
--- /dev/null
+++ b/doc/languages-frameworks/perl.section.md
@@ -0,0 +1,163 @@
+# Perl {#sec-language-perl}
+
+## Running perl programs on the shell {#ssec-perl-running}
+
+When executing a Perl script, it is possible you get an error such as `./myscript.pl: bad interpreter: /usr/bin/perl: no such file or directory`. This happens when the script expects Perl to be installed at `/usr/bin/perl`, which is not the case when using Perl from nixpkgs. You can fix the script by changing the first line to:
+
+```perl
+#!/usr/bin/env perl
+```
+
+to take the Perl installation from the `PATH` environment variable, or invoke Perl directly with:
+
+```ShellSession
+$ perl ./myscript.pl
+```
+
+When the script is using a Perl library that is not installed globally, you might get an error such as `Can't locate DB_File.pm in @INC (you may need to install the DB_File module)`. In that case, you can use `nix-shell` to start an ad-hoc shell with that library installed, for instance:
+
+```ShellSession
+$ nix-shell -p perl perlPackages.DBFile --run ./myscript.pl
+```
+
+If you are always using the script in places where `nix-shell` is available, you can embed the `nix-shell` invocation in the shebang like this:
+
+```perl
+#!/usr/bin/env nix-shell
+#! nix-shell -i perl -p perl perlPackages.DBFile
+```
+
+## Packaging Perl programs {#ssec-perl-packaging}
+
+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](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/perl-modules/generic).
+
+Perl packages from CPAN are defined in [pkgs/top-level/perl-packages.nix](https://github.com/NixOS/nixpkgs/blob/master/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:
+
+```nix
+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
+
+```nix
+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:
+
+```ShellSession
+$ 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:
+
+```ShellSession
+$ 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:
+
+1. 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`
+2. 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.)
+3. In the fixup phase, it writes the propagated build inputs (`propagatedBuildInputs`) to the file `$out/nix-support/propagated-user-env-packages`. `nix-env` recursively installs all packages listed in this file when you install a package that has it. This ensures that a Perl package can find its dependencies.
+
+`buildPerlPackage` is built on top of `stdenv`, so everything can be customised in the usual way. For instance, the `BerkeleyDB` module has a `preConfigure` hook to generate a configuration file used by `Makefile.PL`:
+
+```nix
+{ buildPerlPackage, fetchurl, db }:
+
+buildPerlPackage rec {
+  name = "BerkeleyDB-0.36";
+
+  src = fetchurl {
+    url = "mirror://cpan/authors/id/P/PM/PMQS/${name}.tar.gz";
+    sha256 = "07xf50riarb60l1h6m2dqmql8q5dij619712fsgw7ach04d8g3z1";
+  };
+
+  preConfigure = ''
+    echo "LIB = ${db.out}/lib" > config.in
+    echo "INCLUDE = ${db.dev}/include" >> config.in
+  '';
+}
+```
+
+Dependencies on other Perl packages can be specified in the `buildInputs` and `propagatedBuildInputs` attributes. If something is exclusively a build-time dependency, use `buildInputs`; if it’s (also) a runtime dependency, use `propagatedBuildInputs`. For instance, this builds a Perl module that has runtime dependencies on a bunch of other modules:
+
+```nix
+ClassC3Componentised = buildPerlPackage rec {
+  name = "Class-C3-Componentised-1.0004";
+  src = fetchurl {
+    url = "mirror://cpan/authors/id/A/AS/ASH/${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:
+
+```nix
+{ 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 $out/bin/exiftool
+  '';
+};
+```
+
+This will remove the `-I` flags from the shebang line, rewrite them in the `use lib` form, and put them on the next line instead. This function can be given any number of Perl scripts as arguments; it will modify them in-place.
+
+### Generation from CPAN {#ssec-generation-from-CPAN}
+
+Nix expressions for Perl packages can be generated (almost) automatically from CPAN. This is done by the program `nix-generate-from-cpan`, which can be installed as follows:
+
+```ShellSession
+$ 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:
+
+```ShellSession
+$ nix-generate-from-cpan XML::Simple
+  XMLSimple = buildPerlPackage rec {
+    name = "XML-Simple-2.22";
+    src = fetchurl {
+      url = "mirror://cpan/authors/id/G/GR/GRANTM/${name}.tar.gz";
+      sha256 = "b9450ef22ea9644ae5d6ada086dc4300fa105be050a2030ebd4efd28c198eb49";
+    };
+    propagatedBuildInputs = [ XMLNamespaceSupport XMLSAX XMLSAXExpat ];
+    meta = {
+      description = "An API for simple XML files";
+      license = with stdenv.lib.licenses; [ artistic1 gpl1Plus ];
+    };
+  };
+```
+
+The output can be pasted into `pkgs/top-level/perl-packages.nix` or wherever else you need it.
+
+### Cross-compiling modules {#ssec-perl-cross-compilation}
+
+Nixpkgs has experimental support for cross-compiling Perl modules. In many cases, it will just work out of the box, even for modules with native extensions. Sometimes, however, the Makefile.PL for a module may (indirectly) import a native module. In that case, you will need to make a stub for that module that will satisfy the Makefile.PL and install it into `lib/perl5/site_perl/cross_perl/${perl.version}`. See the `postInstall` for `DBI` for an example.
diff --git a/doc/languages-frameworks/perl.xml b/doc/languages-frameworks/perl.xml
deleted file mode 100644
index b017c028f64..00000000000
--- a/doc/languages-frameworks/perl.xml
+++ /dev/null
@@ -1,195 +0,0 @@
-<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>