file_build_uri in includes/file.inc
Constructs a URI to Drupal's default files location given a relative path.
file_create_htaccess in includes/file.inc
Creates a .htaccess file in the given directory.
file_scan_directory in includes/file.inc
Finds all files that match a given mask in a given directory.
file_unmanaged_copy in includes/file.inc
Copies a file to a new location without invoking the file API.
image_style_url in modules/image/image.module
Returns the URL for an image derivative given a style and image path.
user_save in modules/user/user.module
Save changes to a user account or add a new user.