path - How to get the relative directory no matter from where it's included in PHP?

Question

If it's Path_To_DocumentRoot/a/b/c.php,should always be /a/b.

I use this:

dirname($_SERVER["PHP_SELF"])

But it won't work when it's included by another file in a different directory.

EDIT

I need a relative path to document root .It's used in web application.

I find there is another question with the same problem,but no accepted answer yet.

PHP - Convert File system path to URL

Answer 1

Do you have access to $_SERVER['SCRIPT_NAME']? If you do, doing:

dirname($_SERVER['SCRIPT_NAME']);

Should work. Otherwise do this:

In PHP < 5.3:

substr(dirname(__FILE__), strlen($_SERVER['DOCUMENT_ROOT']));

Or PHP >= 5.3:

substr(__DIR__, strlen($_SERVER['DOCUMENT_ROOT']));

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You might need to realpath() and str_replace() all to / to make it fully portable, like this:

substr(str_replace('\', '/', realpath(dirname(__FILE__))), strlen(str_replace('\', '/', realpath($_SERVER['DOCUMENT_ROOT']))));