Yes, this is pretty easy:

$content = file_get_contents("http://www.example.com/something.html");

<?php
$stringtofind = "whatever you are looking for";
$content = file_get_contents("http://www.domain.com/page.html");
$pos = strpos($content,$stringtofind);

if($pos === false) {
// Not found
}
else {
// Found
}
?>

You can fetch the source code with file_get_contents(); function, and you can check if the code line is present with strpos();

Here's the complete script sollution:

<?

// Enter the URL of the page that you want to view the source (replace page.com)

$page = file_get_contents("http://www.page.com");

// Enter code that you are looking for here (replace code)

$search = "code";

// Script will check if code is present on the source code of the URL

$check = strpos($page,$search);

// Post the results

if($check == true)
{
echo "The code is found!";
}
else
{
echo "The code is not found!";
}

?>

P.S. Sorry I cannot wrap it in CODE tags, because code tags will remove the dollar variables, and script will get messy to understand...