>perl -wMstrict -le
"my %hash = qw(a 1 b 2 c 3 d 4);
 print 'foreach loop output:';
 foreach (my ($k, $v) = each %hash) {
   print qq{$k => $v};
   }
 print 'while loop output:';
 keys %hash;
 while (my ($k, $v) = each %hash) {
   print qq{$k => $v};
   }
"
foreach loop output:
c => 3
c => 3
while loop output:
c => 3
a => 1
b => 2
d => 4