Something that has not been mentioned in this thread or in for loops is the reversed form of the for/foreach loop.

my %hash;
my @array = qw( ABC DEF GHI );
$hash{$_}++ for (@array); # $_ is the loop variable.
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This code is no different than the following except that the for comes at the end (and that you are forced to use $_ as the loop variable).

my %hash;
my @array = qw( ABC DEF GHI );
for my $key (@array) {
  $hash{$key}++
}
[download]