preg_match checks whether a string matches the regular expression.
$string = 'This is a string which contains numbers: 12345'; $isMatched = preg_match('%^[a-zA-Z]+: [0-9]+$%', $string); var_dump($isMatched); // bool(true)
If you pass in a third parameter, it will be populated with the matching data of the regular expression:
preg_match('%^([a-zA-Z]+): ([0-9]+)$%', 'This is a string which contains numbers: 12345', $matches); // $matches now contains results of the regular expression matches in an array. echo json_encode($matches); // ["numbers: 12345", "numbers", "12345"]
$matches contains an array of the whole match then substrings in the regular expression bounded by parentheses, in the order of open parenthesis's offset. That means, if you have
/z(a(b))/ as the regular expression, index 0 contains the whole substring
zab, index 1 contains the substring bounded by the outer parentheses
ab and index 2 contains the inner parentheses