my @ary2 = grep {defined} @hash{@ary};

##</code><code>##

#!/usr/bin/perl -w
use strict;

my @ary  = ('a', 'c', 'g', 'l');
my %hash = (a => 1, b => 2, c => 3, d => 4);

my @ary2 = grep {defined} @hash{@ary};

print "[$_]\n" for @ary2;