In Perl5, libraries and classes are implemented using the same mechanism (packages, usually in their own .pm files), but they're completely different. If you're converting P4-style libraries to P5-style, all you need to do is follow this template.

Old:

[mylibrary1.pl]

sub half {
   my $number = shift;
   return $number / 2;
}
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New:

[mylibrary1.pm]

package mylibrary1;

use base 'Exporter';
use vars qw( @EXPORT @EXPORT_OK );

@EXPORT = qw( half ); # These are the ones that are imported if nothin
+g is specified.
@EXPORT_OK = qw( half ); # These are the ones you may specify, if you 
+want.

sub half {
   my $number = shift;
   return $number / 2;
}

1; # All .pm files must end with a true value
__END__
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Now, when you use them, you'll do it like this:

Old way:

[myscript.pl]

require 'mylibrary1.pl';

print half( 10 ), "\n";
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New way:

[myscript.pl]

use mylibrary1 qw( half );

print half( 10 ), "\n";
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Now, the different between @EXPORT and @EXPORT_OK is how you construct the 'use' line. Here's a few examples:

use Foo; # Imports everything in @EXPORT, nothing in @EXPORT_OK

use Foo 'bar'; # Imports 'bar' if it's in @EXPORT_OK. Imports nothing 
+from @EXPORT

use Foo (); # Imports NOTHING from either.
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