What's the difference between exists and defined?

Question

What is the difference between

if (defined $hash{$key}) { }

and

if (exists $hash{$key}) { }

When do I kno

Answer 1

This example shows the difference. In general defined works for any structure and exist is related to hashes.

my %hash=("1"=>undef);
print "exists:".exists($hash{"1"})."\n";
print "defined:".defined($hash{"1"})."\n";

The difference is small and not so obvious, so expect that people will mess with it.