The exec keyword

exists returns true, if an expression that specifies an element of a hash exists, and the specified element in the hash has been initialized to any value (like undef).

Although exists can be called on arrays also, its behaviour strongly depends to the use of delete on arrays, having a much less clear behaviour.

  exists EXPRESSION

print "Exists\n"    if exists $hash{$key};
print "Defined\n"   if defined $hash{$key};
print "True\n"      if $hash{$key};