if ($choice ne 'a', 'r', 'o', 'd', 'e') {
     print "Invalid choice, TRY AGAIN!\n";
}

##</code><code>##

# Very explicit:
if ($choice ne 'a' && $choice ne 'r' && $choice ne 'o' && $choice ne 'd' && $choice ne 'e') {
     print "Invalid choice, TRY AGAIN!\n";
}

# Testing if the element is in a List of options:
unless ( grep { $_ eq $choice } ('a', 'r', 'o', 'd','e') ) {
     print "Invalid choice, TRY AGAIN!\n";
}

# Testing if the element matches a regular expression:
unless ( $choice =~ /^(a|r|o|d|e)$/ ) {
     print "Invalid choice, TRY AGAIN!\n";
}