if ($who !~ /[A-Za-z]/) ...  # thanks to eric256 to point out the problem
if ($who2 !~ /[A-Za-z]/) ... # in my regexp. I really meant to use a negative
                             # regexp. If any character not alphabetical. ^_^

##</code><code>##

if ($email =~ /@/) ...

##</code><code>##

if ($creditcard =~ /^\d{16}$/) ...