UPDATE: I took the "How" at face value instead of interpreting it as a 'Why'. Please disregard this answer.

The simple answer would be: print "bye";. The more serious answer: How do you want to identify the "bye"?. Do you want to get the key for which the value is a pointer to a hash with the key 'later'?

my $result;
foreach my $v (keys %hash) {
if (exists $hash{$v}{'later'}) {
  $result= $v;
}
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Or do you want the second value in the hash? That is not possible. There is no order in a hash, so there is no *second* value

Or do you want to print all hash keys? But that would also print 'hi':

print join(' ',keys %hash);
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Or do you really just want to print the fixed string "bye" no matter what? See my first answer.