Code:
<?php
error_reporting(0);
$url=$_GET['url'];
$string='THE TEXT YOU WANT TO CHECK FOR';
$handle = fopen("$url", "rb");
$contents = stream_get_contents($handle);
$count=substr_count("$contents", "$string");
if($count > 0){
echo "PASS";
}else{
echo "FAIL";
}
?>
This should get you started.