The problem is not with or. The problem is with system(). Unlike functions like open(), unlink(), and chmod(), this does not return a true value on success -- rather, it turns 0 (the shell's version of true) on success, and non-zero on failure. This is documented.

Many people write system(...) == 0 or die to get around this. You can use my Perl 6 module for "fixing" the senses of true and false, found at japhygesis. I'll probably put it on CPAN soon.

japhy -- Perl and Regex Hacker