How to check if a file has changed?

Question

I have an xml file with database information that should be loaded when the script is installed or when the content of the file changes. Can I use md5_file() on the xml file

Answer 1

I know that I am going back in time here, but the question helped me so I want to share what I did with it, so while this is not an answer to the question I will make it a community wiki so it can be improved (I'm no expert).

This was part of a much larger class so I have stripped out the rest and provided just the applicable code and turned it into an easy to follow example using a very common file:

class ApplicationLogger {

    private $logfile, $path;

    public function __construct() {
        $this->logfile  = 'error.log';
        $this->path  = '/var/log/apache2/';
    }

    public function logState() {
        $files = array(
            'target'  => $this->path . $this->logfile,
            'lastmod' => $this->path . $this->logfile . '_lastmod'
        );

        if (file_exists($files['lastmod']) && file_exists($files['target'])) {
            $lfh = fopen($files['lastmod'], 'r');
            while (!feof($lfh)) {
                $lines[] = fgets($lfh);
            }
            fclose($lfh);
        }

        $modified = false;

        /**
         * check if we have a matching hash.
         */
        if (isset($lines) && filemtime($files['target']) != $lines[0]) { // mod time mismatch
            if (md5_file($files['target']) != $lines[1]) { // content modified
                $modified = true;
            }
        }

        /**
         * update or create the lastmod file
         */
        if (!file_exists($files['lastmod']) || $modified) {

            $current_mod = filemtime($files['target']) . "\n" . md5_file($files['target']);

            file_put_contents($files['lastmod'], $current_mod);
            $modified = true;
        }

        return $modified;
    }
}

Usage is straight forward:

$mod = new ApplicationLogger();
if ($mod->logState()) {
    // changed do something
}

Adapt it to your needs, improve it however you see fit. I hope that you will contribute your adaptations by editing this CW.