too long

How can I find with p h p if someone comes to my website from google?

<?php
  if (isset($_COOKIE['source'])) {
      $arr = explode("=",$_COOKIE['source']);
      $_SESSION['source'] = $arr[1];
      unset($_COOKIE['source']);
  }
?>

This is how I get the source, to know where was the visitor before my site and I want to set $_SESSION['source']="google" if he was searching on Google to find my page.

Use: $_SERVER['HTTP_REFERER']

if(strpos($_SERVER['HTTP_REFERER'], 'google'))
echo 'comes from google';

Try checking $_SERVER['HTTP_REFERER']. This global variable should contain the referer url.

This is how I would do it. It parses the given URL if there is any and then removes all unneeded information like Top-Level-Domain or third- or lower level domains, so we only have the second level domain remaining (google).

function isRequestFromGoogle() {
    if (!empty($_SERVER['HTTP_REFERER'])) {
        $host = parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST);
        if (!$host) {
            return false; // no host found
        }

        // remove the TLD, like .com, .de etc.
        $hostWithoutTld = mb_substr($_SERVER['HTTP_REFERER'], 0, mb_strrpos($_SERVER['HTTP_REFERER'], '.'));
        // get only the second level domain name
        // e.g. from news.google.de we already removed .de and now we remove news.
        $domainName = mb_substr($hostWithoutTld, mb_strrpos($hostWithoutTld, '.') + 1);

        if (mb_strtolower($domainName) == 'google') {
            return true;
        } else {
            return false;
        }
    }
}