Is there any difference between __DIR__ and dirname(__FILE__) in PHP?

It looks the same for me,but I'm not sure,

because there are many projects that uses dirname(__FILE__).

Their result is exactly the same ; so, no difference on that.

For example, the two following lines :

var_dump(dirname(__FILE__));
var_dump(__DIR__);

Will both give the same output :

string '/home/squale/developpement/tests/temp' (length=37)

But, there are at least two differences :

• __DIR__ only exists with PHP >= 5.3
  • which is why dirname(__FILE__) is more widely used
• __DIR__ is evaluated at compile-time, while dirname(__FILE__) means a function-call and is evaluated at execution-time
  • so, __DIR__ is (or, should be) faster.

As, as a reference, see the Magic constants section of the manual (quoting) :

__DIR__ : The directory of the file.
If used inside an include, the directory of the included file is returned.
This is equivalent to dirname(__FILE__).
This directory name does not have a trailing slash unless it is the root directory.
(Added in PHP 5.3.0.)