ACF – Compare user and post data

There is a PHP function: preg_grep which accepts $pattern and $input as a parameters and returns you an array of matches. If you want to get first match just assign it to variable, e.x.:

$field_os = array('windows-7','mac-os-10.07','linux-ubunto-16.04');
$user_os_type = "windows";

$matches = preg_grep("https://wordpress.stackexchange.com/" . $user_os_type . "https://wordpress.stackexchange.com/", $field_os);

var_dump($matches);
/*
 Prints:

 array(1) {
  [0]=>
  string(9) "windows-7"
 }

*/

$first_match = $matches[0];

echo $first_match; // Prints: windows-7

For more information visit this link: http://php.net/manual/en/function.preg-grep.php