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. See 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. See 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 (see 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 (see 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.