Why many PHP developers use "__DIR__ . '../otherFolder'"?

Question

Often I see this type of code __DIR__.'/../Resources/config'. But why is the point, am I wrong that is it the same that typing ../Resources/config' ?

Answer 1

No, it's not always the same thing. __DIR__ is the directory of the file, not the current working directory. This code is essentially a dynamically-generated absolute path.

Write this into ~/foo/script.php:

<?php
// Ta, Sven
//  https://php.net/manual/en/function.realpath.php#84012
function get_absolute_path($path) {
    $path = str_replace(array('/', '\\'), DIRECTORY_SEPARATOR, $path);
    $parts = array_filter(explode(DIRECTORY_SEPARATOR, $path), 'strlen');
    $absolutes = array();
    foreach ($parts as $part) {
        if ('.' == $part) continue;
        if ('..' == $part) {
            array_pop($absolutes);
        } else {
            $absolutes[] = $part;
        }
    }
    return '/' . implode(DIRECTORY_SEPARATOR, $absolutes);
}

$p = __DIR__ . '/../bar';
echo $p . "\n" . get_absolute_path($p) . "\n";
?>

Now:

$ cd ~/foo
$ php script.php
/home/me/foo/../bar
/home/me/bar

$ cd ~/
$ php foo/script.php
/home/me/foo/../bar
/home/me/bar

But if we got rid of __DIR__:

$ cd ~/foo
$ php script.php
../bar
/home/me/bar

$ cd ~/
$ php foo/script.php
../bar
/home/bar

See ... that last path is incorrect.

If we were using these paths anywhere, they'd be broken without __DIR__.

Whenever you write a script, you should ensure that it is safe to execute it from some directory other than the one in which it lives!

Answer 2

Because in many cases the relative path won't work, for example when the script is run from some other folder. Using __ DIR __ converts the relative path into absolute path, leaving no space for any confusion.

For your question lets suppose this hierarchy,

/
test/
test/script.php
test/Resource/config
another/

Now script.php contains this path, you run the script from the directory test so the relative path is resolved to test/Resource/config. Its what you wanted.

But if you run the script from say another, then the path will be resolved to another/Resource/config which is not right.

If you have used __DIR__, it always get resolved into the path of the script that it is used in. So the relative path would have become /test/Resource/config

Now no matter from where you run this script, since the path is absolute, it won't be resolved relatively and will remain the same.