$re = '/^(?=[ple]*a[ple]*$)(?=[ape]*l[ape]*$)(?=[apl]*e[apl]*$)[ale]*p[ale]*p[ale]*$/mi';
$str = 'Apple
ppleA
APPLE
apple
ppale
foo
appple
aple
bar
test';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php