Dealing with huge xml file using preg_replace

I was trying to make a "search replace between for a huge xml file (1GB). I found this great code that is work perfectly while using str_replace on my file-

<?php 

function replace_file($path, $string, $replace)
{
    set_time_limit(0);

    if (is_file($path) === true)
    {
        $file = fopen($path, 'r');
        $temp = tempnam('./', 'tmp');

        if (is_resource($file) === true)
        {
            while (feof($file) === false)
            {
 file_put_contents($temp, str_replace($string, $replace, fgets($file)), FILE_APPEND);
            }

            fclose($file);
        }

        unlink($path);
    }

    return rename($temp, $path);
}


replace_file('myfile.xml', '<search>', '<replace>');

so far so good and it works great.

Now I changed the str_replace to preg_replace and the search value to '/^[^]/' so the code looks like this-

<?php 

    function replace_file($path, $string, $replace)
    {
        set_time_limit(0);

        if (is_file($path) === true)
        {
            $file = fopen($path, 'r');
            $temp = tempnam('./', 'tmp');

            if (is_resource($file) === true)
            {
                while (feof($file) === false)
                {
     file_put_contents($temp, preg_replace($string, $replace, fgets($file)), FILE_APPEND);
                }

                fclose($file);
            }

            unlink($path);
        }

        return rename($temp, $path);
    }


    replace_file('myfile.xml', '/[^<search>](.*)[^</search>]/', '<replace>');

I get an error "preg_replace unknown modifier" 'd' on line 16 line 16 is -

file_put_contents($temp, preg_replace($string, $replace, fgets($file)), FILE_APPEND);