$password =~ m/^[DesiredCharactersHere]+$/

Watch out! That permits "Desired\n"! I just zapped someone on the beginners list for that same mistake. Potential Big Security Hole.

Better to use something like: $password !~ /[^DesiredCharactersHere]/ or even not $password =~ tr/DesiredCharactersHere//c.

-- Randal L. Schwartz, Perl hacker