Perl Warts

#!/usr/bin/perl

$x = "moo";
if ($x == "") { print "Please supply input.\n"; }
else { print "You wrote '$x'\n"; }

This program prints "Please supply input.".

The == operator in Perl does not compare strings. So, unexpected values may evaluate as equal. For example, 0 == "moo" is true, as is "moo" == "ribbit".

Use the eq operator to compare strings instead. Or, if you don't know the type of the objects you're comparing, compare their type first and then if they're the same, compare values with an appropriate operator.