I know borisz's y/// is better, but here's a regex TIMTOWTDI entry:

$string_to_match='QWERTAAWAAAAKAAAAAAAA';
$check = substr($string_to_match, -17, 17);
$count = () = ( $check =~ /(A)/g );
if ( $count >= 14)
{ print "correct"; }
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This uses the (undocumented?) ()= "operator" to force m///g to return a list of matches, which then gets converted to a count in $count = ().