get_SERP_name.php

<?php // please don't copy this line. 

/**
 * Get SERP Name
 */
function jiv_get_serp_name() {
  if ( isset( $_SERVER['HTTP_REFERER'] ) ) {
    $serps = array( 'google', 'bing', 'yahoo', 'duckduckgo' );
    $referer = $_SERVER['HTTP_REFERER'];
    $result = jiv_get_domain_from_url( $referer );
    $result = explode( ".", $result );

    if ( in_array( $result[0], $serps ) ) {
      return $result[0];
    } else {
      return false;
    }
  }

  return false;
}

function jiv_get_domain_from_url( $url ) {
  $pieces = parse_url( $url );
  $domain = isset( $pieces['host'] ) ? $pieces['host'] : $pieces['path'];
  if ( preg_match( '/(?P<domain>[a-z0-9][a-z0-9\-]{1,63}\.[a-z\.]{2,6})$/i', $domain, $regs ) ) {
    return $regs['domain'];
  }
  return false;
}