GNU Emacs Lisp Reference Manual
Chapter 22: Files
In Emacs, you can find, create, view, save, and otherwise work with
files and file directories. This chapter describes most of the
file-related functions of Emacs Lisp, but a few others are described in
Buffers, and those related to backups and auto-saving are
described in Backups and Auto-Saving.
Many of the file functions take one or more arguments that are file
names. A file name is actually a string. Most of these functions
expand file name arguments using expand-file-name, so that
~ is handled correctly, as are relative file names (including
../). These functions don't recognize environment variable
substitutions such as $HOME. See File Name Expansion.