I keep the following shell script in my path as 'whichpm' :

#!/bin/sh

echo 'print map { sprintf( "%20s : %s\n", $_, $INC{$_} ) } sort keys %
+INC; print "\n'$1' version : $'$1'::VERSION\n\n"' | perl "-M$1"
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Which yields results such as :

$ whichpm CGI       
              CGI.pm : /System/Library/Perl/5.8.6/CGI.pm
         CGI/Util.pm : /System/Library/Perl/5.8.6/CGI/Util.pm
             Carp.pm : /System/Library/Perl/5.8.6/Carp.pm
         Exporter.pm : /System/Library/Perl/5.8.6/Exporter.pm
         constant.pm : /System/Library/Perl/5.8.6/constant.pm
         overload.pm : /System/Library/Perl/5.8.6/overload.pm
           strict.pm : /System/Library/Perl/5.8.6/strict.pm
             vars.pm : /System/Library/Perl/5.8.6/vars.pm
         warnings.pm : /System/Library/Perl/5.8.6/warnings.pm
warnings/register.pm : /System/Library/Perl/5.8.6/warnings/register.pm

CGI version : 3.05
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