robustly list any Perl code's module dependencies

[Aristotle]

Category:

Utility Scripts

Description:

I just read hans_moleman's script and thought there has to be a more robust way to do this that doesn't rely on parsing sources and has better support for recursive dependencies than just reporting whether a toplevel dependency is satisfied. This module is the surprisingly simple result. It relies on the fact that you can put coderefs in @INC.

Update: podmaster points out that not all pragmas are available everywhere, warnings being an obvious example, so they constitute a depency, too. I don't want to change the behaviour of this module however, therefor I added this to the CAVEATS section in the POD.

#!/usr/bin/perl -w
package ListDependencies;
use strict;
unshift @INC, sub {
        local $_ = $_[1];
        return unless /[[:upper:]]/;
        s/\.pm$//i;
        s/[\/:]/::/g;
        print STDERR $_, $/;
};
1;
__END__

=head1 NAME

ListDependencies.pm - list any Perl code's module dependencies

=head1 SYNOPSIS

perl -c -MListDependencies scriptname
perl -MListDependencies -MModule::Name -e1
perl -MListDependencies -e'use Module::Name'

=head1 DESCRIPTION

This module prints the names of any modules any piece
of Perl code compiled after it tries to load to C<STDERR>,
but ignores C<use pragma;> directives. You should load
this module prior to all others. The C<-M> command line
switch to C<perl> is a good place to do so.

Note that it won't prevent execution of the code you're
trying to examine. If all you want to do is list
dependencies for a piece of standalone code, you may
want to use the C<-c> command line switch to C<perl> to
check compile time dependencies. Be aware that this will
leave you blind to any attempts to load modules
dynamically at runtime.

=head1 CAVEATS

If your own custom modules use all-lowercase names, this
module won't list them. This is intentional:
all-lowercase names are reserved for Perl pragmas.

Note that not all pragmas are available everywhere, so
they may constitute a depency as well. L<warnings> is an
obvious example.

=head1 BUGS

There is no way to specify a different output file handle
than C<STDERR>. A proper version should include an
C<import()> routine to take care of this.

=head1 RESTRICTIONS

The module only honours Unix, DOSish and MacOS directory
separators. A more portable solution would have to rely
on L<File::Spec>, but unfortunately that would require
this module to import modules itself.
Heisenberg's Dispersion Relation applies. :-)

=head1 AUTHOR

Aristotle Pagaltzis <pagaltzis at gmx dot de>

=head1 COPYRIGHT

Copyright 2002. This may be modified and distributed on
the same terms as Perl.

[simonflk]

This is a nice trick, but it won't work if the script or or any modules that are loaded do a use lib or unshift @INC

Something like this should work, as long as require is not overriden elsewhere:

package ShowDependencies;
use strict;

*CORE::GLOBAL::require = \&show_require;

sub show_require (;$)  {
    my $module = shift;
    print STDERR $module, $/;
    my $retval = eval "CORE::require( $module )";
    die $@ if $@;
    return $retval;
}
1;

There is also a module (Module::Dependency) on the CPAN that builds a list of dependencies.

update: added use strict

-- simonflk