PHP Extract Values From One String Based on a Pattern Defined in Another

I have two strings:

$first = '/this/is/a/string';
$second = '/this/:param1/a/:param2';

And I'm trying to get this:

$params = array('param1' => 'is', 'param2' => 'string');

But getting from point a to b is proving more than my tired brain can handle at the moment.

Anything starting with a ':' in the second string defines a variable name/position. There can be any number of variables in $seco开发者_StackOverflow中文版nd which need to be extracted from $first. Segments are separated by a '/'.

---

For fun I'll throw in a slightly different approach. It takes about half the time as cletus's (whose answer is excellent) because it uses less regex and conditionals:

$first = '/this/is/a/string';
$second = '/this/:param1/a/:param2';

$firstParts = explode('/', $first);
$paramKeys = preg_grep('/^:.+/', explode('/', $second));

$params = array();
foreach ($paramKeys as $key => $val) {
    $params[substr($val, 1)] = $firstParts[$key]; 
}

/*
output:
Array
(
    [param1] => is
    [param2] => string
)
*/

---

Input:

$first = '/this/is/a/string';
$second = '/this/:param1/a/:param2';
$src = explode('/', $first);
$req = explode('/', $second);
$params = array();
for ($i = 0; $i < count($req); $i++) {
  if (preg_match('!:(\w+)!', $req[$i], $matches)) {
    $params[$matches[1]] = $i < count($src) ? $src[$i] : null;
  }
}
print_r($params);

Output:

Array
(
    [param1] => is
    [param2] => string
)