You can write the contents of a buffer, or part of a buffer, directly to a file on disk using the
write-region functions. Don’t use these functions to write to files that are being visited; that could cause confusion in the mechanisms for visiting.
command append-to-file start end filename
This function appends the contents of the region delimited by
end in the current buffer to the end of file
filename. If that file does not exist, it is created. This function returns
An error is signaled if you cannot write or create
When called from Lisp, this function is completely equivalent to:
(write-region start end filename t)
command write-region start end filename \&optional append visit lockname mustbenew
This function writes the region delimited by
end in the current buffer into the file specified by
nil, then the command writes the entire buffer contents (not just the accessible portion) to the file and ignores
start is a string, then
write-region writes or appends that string, rather than text from the buffer.
end is ignored in this case.
append is non-
nil, then the specified text is appended to the existing file contents (if any). If
append is a number,
write-region seeks to that byte offset from the start of the file and writes the data from there.
mustbenew is non-
write-region asks for confirmation if
filename names an existing file. If
mustbenew is the symbol
write-region does not ask for confirmation, but instead it signals an error
file-already-exists if the file already exists. Although
write-region normally follows a symbolic link and creates the pointed-to file if the symbolic link is dangling, it does not follow symbolic links if
The test for an existing file, when
excl, uses a special system feature. At least for files on a local disk, there is no chance that some other program could create a file of the same name before Emacs does, without Emacs’s noticing.
t, then Emacs establishes an association between the buffer and the file: the buffer is then visiting that file. It also sets the last file modification time for the current buffer to
filename’s modtime, and marks the buffer as not modified. This feature is used by
save-buffer, but you probably should not use it yourself.
visit is a string, it specifies the file name to visit. This way, you can write the data to one file (
filename) while recording the buffer as visiting another file (
visit). The argument
visit is used in the echo area message and also for file locking;
visit is stored in
buffer-file-name. This feature is used to implement
file-precious-flag; don’t use it yourself unless you really know what you’re doing.
The optional argument
lockname, if non-
nil, specifies the file name to use for purposes of locking and unlocking, overriding
visit for that purpose.
write-region converts the data which it writes to the appropriate file formats specified by
buffer-file-format and also calls the functions in the list
write-region-annotate-functions. See Format Conversion.
write-region displays the message ‘
Wrote filename’ in the echo area. This message is inhibited if
visit is neither
nil nor a string, or if Emacs is operating in batch mode (see Batch Mode). This feature is useful for programs that use files for internal purposes, files that the user does not need to know about.
If this variable’s value is
write-region uses the
fsync system call after writing a file. Although this slows Emacs down, it lessens the risk of data loss after power failure. If the value is
t, Emacs does not use
fsync. The default value is
nil when Emacs is interactive, and
t when Emacs runs in batch mode. See Files and Storage.
macro with-temp-file file body…
with-temp-file macro evaluates the
body forms with a temporary buffer as the current buffer; then, at the end, it writes the buffer contents into file
file. It kills the temporary buffer when finished, restoring the buffer that was current before the
with-temp-file form. Then it returns the value of the last form in
The current buffer is restored even in case of an abnormal exit via
throw or error (see Nonlocal Exits).
with-temp-buffer in The Current Buffer.