Well, you could always do something like this:

my $file = "$op.pm";
$file =~ s/::/\//g; # / on *nix, \ on windows, etc.  the point is: you
+r local path separator
require $file;
[download]

Roughly the same, but no eval. However, if you actually use this regexp on the modulename: /^[\w:]+$/s, then I'm pretty certain that it's not possible to put in anything that could be bad.