<?php
$target_url = 'http://example.com/?test={test123}';
$target_query = [];
$parsed_url = parse_url($target_url);
$result_url = null;

if(isset($parsed_url['query'])) {
    parse_str($parsed_url['query'], $target_query);

    foreach ($_GET as $key => $value) {
        foreach ($target_query as $t_key => $t_value) {
            if($t_value == "{{$key}}") {
                $target_query[$t_key] = $value;
            }
        }
    }

    $result_url = $parsed_url['scheme'] . '://' . $parsed_url['host'] . $parsed_url['path'] . '?' . http_build_query($target_query);
} else {
    $result_url = $target_url;
}


header('Location: ' . $result_url);
?>