(emacs)Auto Save Files
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Auto-saving does not normally save in the files that you visited,
because it can be very undesirable to save a program that is in an
inconsistent state when you have made half of a planned change.
Instead, auto-saving is done in a different file called the "auto-save
file", and the visited file is changed only when you request saving
explicitly (such as with `C-x C-s').
Normally, the auto-save file name is made by appending `#' to the
front and rear of the visited file name. Thus, a buffer visiting file
`foo.c' is auto-saved in a file `#foo.c#'. Most buffers that are not
visiting files are auto-saved only if you request it explicitly; when
they are auto-saved, the auto-save file name is made by appending `#%'
to the front and `#' to the rear of buffer name. For example, the
`*mail*' buffer in which you compose messages to be sent is auto-saved
in a file named `#%*mail*#'. Auto-save file names are made this way
unless you reprogram parts of Emacs to do something different (the
functions `make-auto-save-file-name' and `auto-save-file-name-p'). The
file name to be used for auto-saving in a buffer is calculated when
auto-saving is turned on in that buffer.
If you want auto-saving to be done in the visited file, set the
variable `auto-save-visited-file-name' to be non-`nil'. In this mode,
there is really no difference between auto-saving and explicit saving.
A buffer's auto-save file is deleted when you save the buffer in its
visited file. To inhibit this, set the variable
`delete-auto-save-files' to `nil'. Changing the visited file name with
`C-x C-w' or `set-visited-file-name' renames any auto-save file to go
with the new visited name.
When you delete a large amount of a buffer's text, auto-saving turns
off in that buffer. This is because if you deleted the text
unintentionally, you might find the auto-save file more useful if it
contains the deleted text. To restart auto-saving in that buffer, use
`M-x auto-save' with a positive argument.
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