using unix system to make file diff

diff

/**
     * @brief Find the difference between two strings, lines assumed to be separated by "\n|
     * @param $new string The new string
     * @param $old string The old string
     * @return string Human-readable output as produced by the Unix diff command,
     * or "No changes" if the strings are the same.
     * @throws Exception
     */
    public function diff($new, $old)
    {
        $oldfile = '/tmp/old.txt';
        $newfile = '/tmp/new.txt';
        if (! file_put_contents($oldfile, $old)) {
            throw new \Exception('diff failed to write temporary file: ' .
                print_r(error_get_last(), true));
        }
        if (! file_put_contents($newfile, $new)) {
            throw new \Exception('diff failed to write temporary file: ' .
                print_r(error_get_last(), true));
        }
        $answer = array();
        $cmd = "diff $newfile $oldfile";
        exec($cmd, $answer, $retcode);
        unlink($newfile);
        unlink($oldfile);
        if ($retcode != 0) {
            throw new \Exception('diff failed with return code ' . $retcode);
        }
        if (empty($answer)) {
            return 'No changes';
        } else {
            return implode("\n", $answer);
        }
    }