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

Your best bet would be to store the file mod time and compare it to a file mod time you check in the future.

if(filemtime('myfile.txt') > $result_set['filemtime']) {
    // file was modified
}

I have hope that you can do the databasing yourself.

Answer 2

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.

Answer 3

Perhaps you could use PHP's filemtime() function. Simply put, this function gets file modification time for a specified file.

This function returns a unix time stamp, so you'll need to save the last known modification time somewhere in order to compare it to the new value.

$modifiedTs = filemtime($filename);
if ($modifiedTs != $lastModificationTs){
  echo "$filename was modified!";
}

Answer 4

The simpliest way is to compare the file_date - you can use filemtime for this

Answer 5

It depends on what you mean by "changed". If you require that the contents actually be modified, then checking filemtime is not enough - it's a fantastic first step, and should be used first, but it is not sufficient on its own.

Conbine the filemtime with a hash of the file's contents (such as md5_file) and it will work efficiently.