Get a script's public URL relative to the domain

public_relative_url.php

<?php

// Ensure document root superglobal contains no trailing slash
$_SERVER[ 'DOCUMENT_ROOT' ] = rtrim( $_SERVER[ 'DOCUMENT_ROOT' ], '\/' );

// Get current script directory
$this_dir = dirname( __FILE__ );

// Get a public, domain relative, path to current script directory
$this_public = substr( $this_dir, strlen( $_SERVER[ 'DOCUMENT_ROOT' ] ) );

// If substr returns false, point to the public root directory
$this_public = $this_public ? $this_public : '/';