for     (my $i=1; $i<=3; $i++) { print $i }
foreach (my $i=1; $i<=3; $i++) { print $i }

my @array = (1..3);

for     (@array) { print }
foreach (@array) { print }

my %hash  = (1,1,2,2,3,3);

for     (sort keys %hash) { print }
foreach (sort keys %hash) { print }