file_exists() returns false, but the file DOES exist

Question

I\'m having a very weird issue with file_exists(). I\'m using this function to check if 2 different files in the same folders do exist. I\'ve double-checked, they BOTH do ex

Answer 1

In my case, the problem was a misconception of how file_exists() behaves with symbolic links and .. ("dotdot" or double period) parent dir references. In that regard, it differs from functions like require, include or even mkdir().

Given this directory structure:

/home/me/work/example/
  www/
/var/www/example.local/
  tmp/
  public_html -> /home/me/work/example/www/

file_exists('/var/www/example.local/public_html/../tmp/'); would return FALSE even though the subdir exists as we see, because the function traversed up into /home/me/work/example/ which does not have that subdir.

---

For this reason, I have created this function:

/**
 * Resolve any ".." ("dotdots" or double periods) in a given path.
 *
 * This is especially useful for avoiding the confusing behavior `file_exists()`
 * shows with symbolic links.
 *
 * @param string $path
 *
 * @return string
 */
function resolve_dotdots( string $path ) {

    if (empty($path)) {
        return $path;
    }

    $source = array_reverse(explode(DIRECTORY_SEPARATOR, $path));
    $balance = 0;
    $parts = array();

    // going backwards through the path, keep track of the dotdots and "work
    // them off" by skipping a part. Only take over the respective part if the
    // balance is at zero.
    foreach ($source as $part) {
        if ($part === '..') {
            $balance++;

        } else if ($balance > 0) {
            $balance--;

        } else {
            array_push($parts, $part);
        }
    }

    // special case: path begins with too many dotdots, references "outside
    // knowledge".
    if ($balance > 0) {
        for ($i = 0; $i < $balance; $i++) {
            array_push($parts, '..');
        }
    }

    $parts = array_reverse($parts);
    return implode(DIRECTORY_SEPARATOR, $parts);
}