That code should work fine no matter the Perl version. Since you're getting a warning, I doubt that is your full test script - can you show an SSCCE? I suspect there is a difference between your two machines and/or in how Perl is set up. What's the Perl version on your old machine? What are the Windows versions of both machines, and are you using cmd.exe on both? Have you tried running perl argtest.pl Hello?