How to extract only parameter value from URL using ONLY Regular Expressions - php

Question

Extract the value of the u2 parameter from this URL using a regular expression. http://www.example.com?u1=US&u2=HA853&u3=HPA
<?php
$subject="http://www.example.com?u1=US&u2=HA853&u3=HPA"; //my url
$pattern='/u2=[0-9A-Za-z]*/'; //R.E that url value is only digit/Alphabet
preg_match($pattern,$subject,$match);
print_r($match[0]);
?>
Output:-
u2=HA853
How can i retrieve only HA853?

Answer 1

The 0 group is everything that the regex matched so either use \K to ignore the previous matches of the regex,
$subject="http://www.example.com?u1=US&u2=HA853&u3=HPA"; //my url
$pattern='/u2=\K[0-9A-Za-z]*/'; //R.E that url value is only digit/Alphabet
preg_match($pattern,$subject,$match);
print_r($match[0]);
or use a second capture group:
...
$pattern='/u2=([0-9A-Za-z]*)/'; //R.E that url value is only digit/Alphabet
...
print_r($match[1]);
Why you'd need to do that though is unclear to me, http://php.net/manual/en/function.parse-str.php, seems like a simpler approach.
$subject="http://www.example.com?u1=US&u2=HA853&u3=HPA";
parse_str($subject, $output);
echo $output['u2'];
Demo: https://3v4l.org/gR4cb

Answer 2

Other way is to use parse_url,http://php.net/manual/en/function.parse-url.php
$subject="http://www.example.com?u1=US&u2=HA853&u3=HPA";
$query_string = parse_url($subject, PHP_URL_QUERY); // get query string
$parameters = explode('&', $query_string); //Explode with &
$array = array(); // define an empty array
foreach($parameters as $val)
{
$param= explode('=', $val);
$array[$param[0]] = $param[1];
}
echo $array['u2']; // outputs HA853
print_r($array);
Array
(
[u1] => US
[u2] => HA853
[u3] => HPA
)