_color_save_stylesheet in modules/color/color.module

Saves the rewritten stylesheet to disk.

drupal_chmod in includes/drupal.inc

Sets the permissions on a file or directory.

file_prepare_directory in includes/file.inc

Checks that the directory exists and is writable.

file_save_htaccess in includes/file.inc

Creates a .htaccess file in the given directory.

file_save_upload in includes/file.inc

Saves a file upload to a new location.

file_unmanaged_copy in includes/file.inc

Copies a file to a new location without database changes or hook invocation.

file_unmanaged_move in includes/file.inc

Moves a file to a new location without database changes or hook invocation. This is a powerful function that in many ways performs like an advanced version of rename().

image_save in includes/image.inc

Closes the image and saves the changes to a file.

system_check_directory in modules/system/system.module

Checks the existence of the directory specified in $form_element.