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Adriano Ferreira > Module-Which-0.0207 > Module::Which



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Module Version: 0.0207   Source   Latest Release: Module-Which-0.05


Module::Which - Finds out which version of Perl modules are installed


  use Module::Which;
  my $info = which('Module::Which', 'YAML', 'XML::', 'DBI', 'DBD::');
  while (my ($mod, $info) = each %$info) {
      print "$mod: $info->{version}\n"; 


Module::Which is the basis of the script which_pm intented to show which version of a Perl module is installed (if it is there at all).

Modules are searched by name (like 'YAML') or by subcategories ('DBD::' means all modules under the DBD subdirectories of your Perl installation, matching both 'DBD::Oracle' and 'DBD::ODBC::Changes').

This module is very simple and most won't need it. But it has been instructive for the author to see how many broken modules one can find under your Perl installation (some which don't accept even a 'require' statement), modules with no version number and documentation files (named '.pm') which do not return a true value.

Well, all that said, this module is no more than automating:

  perl -MInteresting::Module -e 'print $Interesting::Module::VERSION'

or better the one-liner

  perl -e '$pm = shift; eval "require $pm"; print ${"${pm}::VERSION"}' DBI
  my $info = which(@pm)
  my $info = which(@pm, { return => 'ARRAY', verbose => 1 }

Returns an array ref with information about the modules specified (by name or '::*' patterns). This information is a hash ref which actually contains:

   pm: (the name of the Perl module)
   version: (the installed version)

The version is the one found by accessing the scalar variable $VERSION of the package, after a require statement. If the module was not found, 'version' is undef. If the module has no $VERSION, 'version' is 'undef' (the string). If the 'require' statement failed, 'version' is 'unknown'.

A hash ref of options can be given as the last argument. The option return can take one of the values: 'ARRAY', 'HASH', 'HASH(FIRST)', 'HASH(MULTI)', 'HASH(LIST)'. 'HASH' is the default and means to return a hash ref. 'HASH' forces the return of a hash ref where the module name is used as key. 'ARRAY' is used to get an array ref.

The different strategies for returning a hash are different only if the same module is found twice or more times in the current search path. 'HASH' which is the same as 'HASH(FIRST)' only considers the first occurrence. 'HASH(MULTI)' will store multiple values in an array ref (if needed). The problem with MULTI is that sometimes you get a hash ref and sometimes an array ref of hash refs. If 'HASH(LIST)' is used, an array ref will be stored always, even if there is only one occurrence.

The option verbose can be set to turn on and off warnings on requiring the sought modules.


which is exported by default.


Module::Find was my friend to implement this module as a breeze. But I have found some itches and wrote my own Module::Which::List based on this and Module::List by Andrew Main.

After releasing it into CPAN, I found


Module::InstalledVersion has a different approach (it does not run the modules to find out their versions, but extract them via regexes) and does not has a command-line interface which was the main thrust of this distribution. I have been studying the others too.


Known bugs:

Please report bugs via CPAN RT


Adriano R. Ferreira, <>


Copyright (C) 2005-2007 by Adriano R. Ferreira

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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