php - Only use http refer if from certain page -

i using following code display string url , works fine. however, want use code if initial refering page search page:

<?php      session_start();     if ( !isset( $_session["origurl"] ) )     $_session["origurl"] = $_server["http_referer"];      $mysearchterm = $_server["http_referer"];      $whatiwant = substr($mysearchterm, strpos($mysearchterm, "=") +1);          echo  $whatiwant;     ?>