PHP: Can include a file that file_exists() says doesn't exist

Question

In my script, I set the include path (so another part of the application can include files too), check that a file exists, and include it.

However, after I set the include path, file_exists() reports that the file does not exist, yet I can still include the same file.

<?php
  $include_path = realpath('path/to/some/directory');
  if(!is_string($include_path) || !is_dir($include_path))
  {
    return false;
  }
  set_include_path(
    implode(PATH_SEPARATOR, array(
      $include_path,
      get_include_path()
    ))
  );
  // Bootstrap file is located at: "path/to/some/directory/bootstrap.php".
  $bootstrap = 'bootstrap.php';

  // Returns "bool(true)".
  var_dump(file_exists($include_path . '/' . $bootstrap));
  // Returns "bool(false)".
  var_dump(file_exists($bootstrap));

  // This led me to believe that the include path was not being set properly.
  // But it is. The next thing is what puzzles me.

  require_once $bootstrap;
  // Not only are there no errors, but the file is included successfully!

I can edit the include path and include files without providing the absolute filepath, but I cannot check whether they exist or not. This is really annoying as every time a file that does not exist is called, my application results in a fatal error, or at best a warning (using include_once()).

Turning errors and warnings off is not an option, unfortunately.

Can anyone explain what is causing this behaviour?

Thanks in advance, mniz.

Answer 1

file_exists does nothing more than say whether a file exists (and the script is allowed to know it exists), resolving the path relative to the cwd. It does not care about the include path.