sub mod2file {

    my $modname = shift or return undef;

    my $filename = ($modname !~ m|^(.*/)?[^/]*\.[^/]*$|) ?
        "$modname.pm" : $modname;

    $filename =~ s|^(.*/)||; # Strip leading path info ...
    my $startpath = $1;      # ... but save it in $startpath.

    $filename =~ s|::|/|g;

    return "$startpath$filename"
        if($modname =~ m|/| and -e "$startpath$filename");

    foreach my $basedir ('.', @INC) {
        return "$basedir/$filename"
            if(-e "$basedir/$filename");
    }

    return undef;

}