$re = '/^.*-([0-9]{2,4})\b.*/m';
$str = 'ABC-L-W7P-1423
ABC-L-W7E-87
CH-L-W7-756
CH-M-311-MM';
$subst = "$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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