elisp: Buffer File Name
26.4 Buffer File Name
=====================
The “buffer file name” is the name of the file that is visited in that
buffer. When a buffer is not visiting a file, its buffer file name is
‘nil’. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently. 
Visiting Files.
-- Function: buffer-file-name &optional buffer
This function returns the absolute file name of the file that
BUFFER is visiting. If BUFFER is not visiting any file,
‘buffer-file-name’ returns ‘nil’. If BUFFER is not supplied, it
defaults to the current buffer.
(buffer-file-name (other-buffer))
⇒ "/usr/user/lewis/manual/files.texi"
-- Variable: buffer-file-name
This buffer-local variable contains the name of the file being
visited in the current buffer, or ‘nil’ if it is not visiting a
file. It is a permanent local variable, unaffected by
‘kill-all-local-variables’.
buffer-file-name
⇒ "/usr/user/lewis/manual/buffers.texi"
It is risky to change this variable’s value without doing various
other things. Normally it is better to use ‘set-visited-file-name’
(see below); some of the things done there, such as changing the
buffer name, are not strictly necessary, but others are essential
to avoid confusing Emacs.
-- Variable: buffer-file-truename
This buffer-local variable holds the abbreviated truename of the
file visited in the current buffer, or ‘nil’ if no file is visited.
It is a permanent local, unaffected by ‘kill-all-local-variables’.
Truenames, and abbreviate-file-name.
-- Variable: buffer-file-number
This buffer-local variable holds the file number and directory
device number of the file visited in the current buffer, or ‘nil’
if no file or a nonexistent file is visited. It is a permanent
local, unaffected by ‘kill-all-local-variables’.
The value is normally a list of the form ‘(FILENUM DEVNUM)’. This
pair of numbers uniquely identifies the file among all files
accessible on the system. See the function ‘file-attributes’, in
File Attributes, for more information about them.
If ‘buffer-file-name’ is the name of a symbolic link, then both
numbers refer to the recursive target.
-- Function: get-file-buffer filename
This function returns the buffer visiting file FILENAME. If there
is no such buffer, it returns ‘nil’. The argument FILENAME, which
must be a string, is expanded (File Name Expansion), then
compared against the visited file names of all live buffers. Note
that the buffer’s ‘buffer-file-name’ must match the expansion of
FILENAME exactly. This function will not recognize other names for
the same file.
(get-file-buffer "buffers.texi")
⇒ #<buffer buffers.texi>
In unusual circumstances, there can be more than one buffer
visiting the same file name. In such cases, this function returns
the first such buffer in the buffer list.
-- Function: find-buffer-visiting filename &optional predicate
This is like ‘get-file-buffer’, except that it can return any
buffer visiting the file _possibly under a different name_. That
is, the buffer’s ‘buffer-file-name’ does not need to match the
expansion of FILENAME exactly, it only needs to refer to the same
file. If PREDICATE is non-‘nil’, it should be a function of one
argument, a buffer visiting FILENAME. The buffer is only
considered a suitable return value if PREDICATE returns non-‘nil’.
If it can not find a suitable buffer to return,
‘find-buffer-visiting’ returns ‘nil’.
-- Command: set-visited-file-name filename &optional no-query
along-with-file
If FILENAME is a non-empty string, this function changes the name
of the file visited in the current buffer to FILENAME. (If the
buffer had no visited file, this gives it one.) The _next time_
the buffer is saved it will go in the newly-specified file.
This command marks the buffer as modified, since it does not (as
far as Emacs knows) match the contents of FILENAME, even if it
matched the former visited file. It also renames the buffer to
correspond to the new file name, unless the new name is already in
use.
If FILENAME is ‘nil’ or the empty string, that stands for “no
visited file”. In this case, ‘set-visited-file-name’ marks the
buffer as having no visited file, without changing the buffer’s
modified flag.
Normally, this function asks the user for confirmation if there
already is a buffer visiting FILENAME. If NO-QUERY is non-‘nil’,
that prevents asking this question. If there already is a buffer
visiting FILENAME, and the user confirms or NO-QUERY is non-‘nil’,
this function makes the new buffer name unique by appending a
number inside of ‘<...>’ to FILENAME.
If ALONG-WITH-FILE is non-‘nil’, that means to assume that the
former visited file has been renamed to FILENAME. In this case,
the command does not change the buffer’s modified flag, nor the
buffer’s recorded last file modification time as reported by
‘visited-file-modtime’ (Modification Time). If
ALONG-WITH-FILE is ‘nil’, this function clears the recorded last
file modification time, after which ‘visited-file-modtime’ returns
zero.
When the function ‘set-visited-file-name’ is called interactively,
it prompts for FILENAME in the minibuffer.
-- Variable: list-buffers-directory
This buffer-local variable specifies a string to display in a
buffer listing where the visited file name would go, for buffers
that don’t have a visited file name. Dired buffers use this
variable.
Info Catalog
elisp: Buffer Names
elisp: Buffers
elisp: Buffer Modification