How to extract character parts from string in PHP

$str = "abc123d45ef6g7";
$n = preg_match_all('/[a-zA-Z]*/', $str, $matches);
if ($n) {
 echo implode("", $matches[0]);
}
?>

Attachment: Remove all letters echo preg_replace('/[^a-z]/i', '', $str1);

Only take the first letter echo preg_replace('/^([a-z]+).*/i', '$1', $str1);