Resolve a relative path in a URL with PHP

Question

Example 1: domain.com/dir_1/dir_2/dir_3/./../../../
Should resolve naturally in the browser into = domain.com/

Example 2: domain.c

Answer 1

This is a more simple problem then you are thinking about it. All you need to do is explode() on the / character, and parse out all of the individual segments using a stack. As you traverse the array from left to right, if you see ., do nothing. If you see .., pop an element from the stack. Otherwise, push an element onto the stack.

$str = 'domain.com/dir_1/dir_2/dir_3/./../../../';
$array = explode( '/', $str);
$domain = array_shift( $array);

$parents = array();
foreach( $array as $dir) {
    switch( $dir) {
        case '.':
        // Don't need to do anything here
        break;
        case '..':
            array_pop( $parents);
        break;
        default:
            $parents[] = $dir;
        break;
    }
}

echo $domain . '/' . implode( '/', $parents);

This will properly resolve the URLs in all of your test cases.

Note that error checking is left as an exercise to the user (i.e. when the $parents stack is empty and you try to pop something off of it).