I would have to run perl 5.005

A use VERSION; statement just specifies the minimum Perl version needed. There have been some changes that aren't backwards compatible (usually with deprecation cycles), but to know if you're encountering any of those, you'd have to tell us exactly what problems you're having. Also, note that even old versions of Perl are available via perlbrew. Update: For some general advice on moving from an older to a newer Perl, see e.g. [SOLVED]:Upgrading Perl 5.8 program to 5.22.