Just to amplify a little - you should always use strictures (use strict; use warnings) because they give you early warning about issues. Those issues may be as simple as a typo, or more subtle as in your case. Use strictures with every Perl program you write and take note of any errors or warnings that are produced.

Unfortunately, Perl somewhat goes back to the philosophy held by an early (and probably apocryphal) COBOL compiler which, when given a copy of Lincoln's Gettysburg Address as input, “compiled it.”

The philosophy of “there's more than one way to do it” presupposes that the writer knew what he was doing and that your (the computer's) interpretation is, if not correct, at least plausible. This is not necessarily the case.

So you just need to begin every Perl program-file with... "shebang ... use strict ... use warnings ..."