@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003,
+@c 2004, 2005, 2006 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/files
@node Files, Backups and Auto-Saving, Documentation, Top
@ref{Buffers}, and those related to backups and auto-saving are
described in @ref{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 by calling @code{expand-file-name}, so that
+@file{~} is handled correctly, as are relative file names (including
+@samp{../}). These functions don't recognize environment variable
+substitutions such as @samp{$HOME}. @xref{File Name Expansion}.
+
+ When file I/O functions signal Lisp errors, they usually use the
+condition @code{file-error} (@pxref{Handling Errors}). The error
+message is in most cases obtained from the operating system, according
+to locale @code{system-message-locale}, and decoded using coding system
+@code{locale-coding-system} (@pxref{Locales}).
+
@menu
* Visiting Files:: Reading files into Emacs buffers for editing.
* Saving Buffers:: Writing changed buffers back into files.
* File Locks:: Locking and unlocking files, to prevent
simultaneous editing by two people.
* Information about Files:: Testing existence, accessibility, size of files.
-* Changing File Attributes:: Renaming files, changing protection, etc.
+* Changing Files:: Renaming files, changing protection, etc.
* File Names:: Decomposing and expanding file names.
* Contents of Directories:: Getting a list of the files in a directory.
* Create/Delete Dirs:: Creating and Deleting Directories.
* Magic File Names:: Defining "magic" special handling
for certain file names.
-* Files and MS-DOS:: Distinguishing text and binary files on MS-DOS.
+* Format Conversion:: Conversion to and from various file formats.
@end menu
@node Visiting Files
In spite of the distinction between files and buffers, people often
refer to a file when they mean a buffer and vice-versa. Indeed, we say,
-``I am editing a file,'' rather than, ``I am editing a buffer which I
+``I am editing a file,'' rather than, ``I am editing a buffer that I
will soon save as a file of the same name.'' Humans do not usually need
to make the distinction explicit. When dealing with a computer program,
however, it is good to keep the distinction in mind.
functions and variables that access the visited file name of a buffer or
that find an existing buffer by its visited file name.
-@deffn Command find-file filename
+ In a Lisp program, if you want to look at the contents of a file but
+not alter it, the fastest way is to use @code{insert-file-contents} in a
+temporary buffer. Visiting the file is not necessary and takes longer.
+@xref{Reading from Files}.
+
+@deffn Command find-file filename &optional wildcards
This command selects a buffer visiting the file @var{filename},
-using an existing buffer if there is one, and otherwise creating a
+using an existing buffer if there is one, and otherwise creating a
new buffer and reading the file into it. It also returns that buffer.
-The body of the @code{find-file} function is very simple and looks
-like this:
+Aside from some technical details, the body of the @code{find-file}
+function is basically equivalent to:
-@example
-(switch-to-buffer (find-file-noselect filename))
-@end example
+@smallexample
+(switch-to-buffer (find-file-noselect filename nil nil wildcards))
+@end smallexample
@noindent
(See @code{switch-to-buffer} in @ref{Displaying Buffers}.)
+If @var{wildcards} is non-@code{nil}, which is always true in an
+interactive call, then @code{find-file} expands wildcard characters in
+@var{filename} and visits all the matching files.
+
When @code{find-file} is called interactively, it prompts for
@var{filename} in the minibuffer.
@end deffn
-@defun find-file-noselect filename
+@defun find-file-noselect filename &optional nowarn rawfile wildcards
This function is the guts of all the file-visiting functions. It finds
or creates a buffer visiting the file @var{filename}, and returns it.
It uses an existing buffer if there is one, and otherwise creates a new
buffer and reads the file into it. You may make the buffer current or
display it in a window if you wish, but this function does not do so.
+If @var{wildcards} is non-@code{nil},
+then @code{find-file-noselect} expands wildcard
+characters in @var{filename} and visits all the matching files.
+
When @code{find-file-noselect} uses an existing buffer, it first
verifies that the file has not changed since it was last visited or
saved in that buffer. If the file has changed, then this function asks
the user whether to reread the changed file. If the user says
@samp{yes}, any changes previously made in the buffer are lost.
-If @code{find-file-noselect} needs to create a buffer, and there is no
-file named @var{filename}, it displays the message @samp{New file} in
-the echo area, and leaves the buffer empty.
-
-The @code{find-file-noselect} function calls @code{after-find-file}
-after reading the file (@pxref{Subroutines of Visiting}). That function
-sets the buffer major mode, parses local variables, warns the user if
-there exists an auto-save file more recent than the file just visited,
-and finishes by running the functions in @code{find-file-hooks}.
-
-The @code{find-file-noselect} function returns the buffer that is
-visiting the file @var{filename}.
+This function displays warning or advisory messages in various peculiar
+cases, unless the optional argument @var{nowarn} is non-@code{nil}. For
+example, if it needs to create a buffer, and there is no file named
+@var{filename}, it displays the message @samp{(New file)} in the echo
+area, and leaves the buffer empty.
+
+The @code{find-file-noselect} function normally calls
+@code{after-find-file} after reading the file (@pxref{Subroutines of
+Visiting}). That function sets the buffer major mode, parses local
+variables, warns the user if there exists an auto-save file more recent
+than the file just visited, and finishes by running the functions in
+@code{find-file-hook}.
+
+If the optional argument @var{rawfile} is non-@code{nil}, then
+@code{after-find-file} is not called, and the
+@code{find-file-not-found-functions} are not run in case of failure. What's
+more, a non-@code{nil} @var{rawfile} value suppresses coding system
+conversion (@pxref{Coding Systems}) and format conversion (@pxref{Format
+Conversion}).
+
+The @code{find-file-noselect} function usually returns the buffer that
+is visiting the file @var{filename}. But, if wildcards are actually
+used and expanded, it returns a list of buffers that are visiting the
+various files.
@example
@group
@end example
@end defun
-@deffn Command find-alternate-file filename
-This command selects a buffer visiting the file @var{filename}, then
-kills the buffer that was previously displayed in the selected window.
-It is useful if you have visited the wrong file by mistake, so that you
-can get rid of the buffer that you did not want to create, at the same
-time as you visit the file you intended.
-
-When this command is called interactively, it prompts for @var{filename}.
-@end deffn
-
-@deffn Command find-file-other-window filename
+@deffn Command find-file-other-window filename &optional wildcards
This command selects a buffer visiting the file @var{filename}, but
does so in a window other than the selected window. It may use another
existing window or split a window; see @ref{Displaying Buffers}.
@var{filename}.
@end deffn
-@deffn Command find-file-read-only filename
+@deffn Command find-file-read-only filename &optional wildcards
This command selects a buffer visiting the file @var{filename}, like
@code{find-file}, but it marks the buffer as read-only. @xref{Read Only
Buffers}, for related functions and variables.
@end deffn
@deffn Command view-file filename
-This command views @var{filename} in View mode, returning to the
-previous buffer when done. View mode is a mode that allows you to skim
-rapidly through the file but does not let you modify it. Entering View
-mode runs the normal hook @code{view-mode-hook}. @xref{Hooks}.
+This command visits @var{filename} using View mode, returning to the
+previous buffer when you exit View mode. View mode is a minor mode that
+provides commands to skim rapidly through the file, but does not let you
+modify the text. Entering View mode runs the normal hook
+@code{view-mode-hook}. @xref{Hooks}.
When @code{view-file} is called interactively, it prompts for
@var{filename}.
@end deffn
-@defvar find-file-hooks
+@tindex find-file-wildcards
+@defopt find-file-wildcards
+If this variable is non-@code{nil}, then the various @code{find-file}
+commands check for wildcard characters and visit all the files that
+match them (when invoked interactively or when their @var{wildcards}
+argument is non-@code{nil}). If this option is @code{nil}, then
+the @code{find-file} commands ignore their @var{wildcards} argument
+and never treat wildcard characters specially.
+@end defopt
+
+@defvar find-file-hook
The value of this variable is a list of functions to be called after a
file is visited. The file's local-variables specification (if any) will
have been processed before the hooks are run. The buffer visiting the
file is current when the hook functions are run.
-This variable works just like a normal hook, but we think that renaming
-it would not be advisable.
+This variable is a normal hook. @xref{Hooks}.
@end defvar
-@defvar find-file-not-found-hooks
+@defvar find-file-not-found-functions
The value of this variable is a list of functions to be called when
@code{find-file} or @code{find-file-noselect} is passed a nonexistent
file name. @code{find-file-noselect} calls these functions as soon as
already set up.
This is not a normal hook because the values of the functions are
-used and they may not all be called.
+used, and in many cases only some of the functions are called.
@end defvar
@node Subroutines of Visiting
@comment node-name, next, previous, up
@subsection Subroutines of Visiting
- The @code{find-file-noselect} function uses the
-@code{create-file-buffer} and @code{after-find-file} functions as
-subroutines. Sometimes it is useful to call them directly.
+ The @code{find-file-noselect} function uses two important subroutines
+which are sometimes useful in user Lisp code: @code{create-file-buffer}
+and @code{after-find-file}. This section explains how to use them.
@defun create-file-buffer filename
This function creates a suitably named buffer for visiting
@strong{Please note:} @code{create-file-buffer} does @emph{not}
associate the new buffer with a file and does not select the buffer.
+It also does not use the default major mode.
@example
@group
It uses @code{generate-new-buffer} (@pxref{Creating Buffers}).
@end defun
-@defun after-find-file &optional error warn
+@defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes
This function sets the buffer major mode, and parses local variables
(@pxref{Auto Major Mode}). It is called by @code{find-file-noselect}
and by the default revert function (@pxref{Reverting}).
If reading the file got an error because the file does not exist, but
its directory does exist, the caller should pass a non-@code{nil} value
for @var{error}. In that case, @code{after-find-file} issues a warning:
-@samp{(New File)}. For more serious errors, the caller should usually not
+@samp{(New file)}. For more serious errors, the caller should usually not
call @code{after-find-file}.
If @var{warn} is non-@code{nil}, then this function issues a warning
if an auto-save file exists and is more recent than the visited file.
+If @var{noauto} is non-@code{nil}, that says not to enable or disable
+Auto-Save mode. The mode remains enabled if it was enabled before.
+
+If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that
+means this call was from @code{revert-buffer}. This has no direct
+effect, but some mode functions and hook functions check the value
+of this variable.
+
+If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's
+major mode, don't process local variables specifications in the file,
+and don't run @code{find-file-hook}. This feature is used by
+@code{revert-buffer} in some cases.
+
The last thing @code{after-find-file} does is call all the functions
-in @code{find-file-hooks}.
+in the list @code{find-file-hook}.
@end defun
@node Saving Buffers
@code{save-buffer} is responsible for making backup files. Normally,
@var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup
-file only if this is the first save or if the buffer was previously
-modified. Other values for @var{backup-option} request the making of
-backup files in other circumstances:
+file only if this is the first save since visiting the file. Other
+values for @var{backup-option} request the making of backup files in
+other circumstances:
@itemize @bullet
@item
With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the
@code{save-buffer} function unconditionally backs up the previous
version of the file before saving it.
+
+@item
+With an argument of 0, unconditionally do @emph{not} make any backup file.
@end itemize
@end deffn
-@deffn Command save-some-buffers &optional save-silently-p exiting
+@deffn Command save-some-buffers &optional save-silently-p pred
+@anchor{Definition of save-some-buffers}
This command saves some modified file-visiting buffers. Normally it
asks the user about each buffer. But if @var{save-silently-p} is
non-@code{nil}, it saves all the file-visiting buffers without querying
the user.
-The optional @var{exiting} argument, if non-@code{nil}, requests this
-function to offer also to save certain other buffers that are not
-visiting files. These are buffers that have a non-@code{nil} local
-value of @code{buffer-offer-save}. (A user who says yes to saving one
-of these is asked to specify a file name to use.) The
-@code{save-buffers-kill-emacs} function passes a non-@code{nil} value
-for this argument.
+The optional @var{pred} argument controls which buffers to ask about
+(or to save silently if @var{save-silently-p} is non-@code{nil}).
+If it is @code{nil}, that means to ask only about file-visiting buffers.
+If it is @code{t}, that means also offer to save certain other non-file
+buffers---those that have a non-@code{nil} buffer-local value of
+@code{buffer-offer-save} (@pxref{Killing Buffers}). A user who says
+@samp{yes} to saving a non-file buffer is asked to specify the file
+name to use. The @code{save-buffers-kill-emacs} function passes the
+value @code{t} for @var{pred}.
+
+If @var{pred} is neither @code{t} nor @code{nil}, then it should be
+a function of no arguments. It will be called in each buffer to decide
+whether to offer to save that buffer. If it returns a non-@code{nil}
+value in a certain buffer, that means do offer to save that buffer.
@end deffn
-@defvar buffer-offer-save
-When this variable is non-@code{nil} in a buffer, Emacs offers to save
-the buffer on exit even if the buffer is not visiting a file. The
-variable is automatically local in all buffers. Normally, Mail mode
-(used for editing outgoing mail) sets this to @code{t}.
-@end defvar
-
-@deffn Command write-file filename
+@deffn Command write-file filename &optional confirm
+@anchor{Definition of write-file}
This function writes the current buffer into file @var{filename}, makes
the buffer visit that file, and marks it not modified. Then it renames
the buffer based on @var{filename}, appending a string like @samp{<2>}
if necessary to make a unique buffer name. It does most of this work by
-calling @code{set-visited-file-name} and @code{save-buffer}.
+calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and
+@code{save-buffer}.
+
+If @var{confirm} is non-@code{nil}, that means to ask for confirmation
+before overwriting an existing file. Interactively, confirmation is
+required, unless the user supplies a prefix argument.
+
+If @var{filename} is an existing directory, or a symbolic link to one,
+@code{write-file} uses the name of the visited file, in directory
+@var{filename}. If the buffer is not visiting a file, it uses the
+buffer name instead.
@end deffn
-@defvar write-file-hooks
+ Saving a buffer runs several hooks. It also performs format
+conversion (@pxref{Format Conversion}), and may save text properties in
+``annotations'' (@pxref{Saving Properties}).
+
+@defvar write-file-functions
The value of this variable is a list of functions to be called before
writing out a buffer to its visited file. If one of them returns
non-@code{nil}, the file is considered already written and the rest of
the functions are not called, nor is the usual code for writing the file
executed.
-If a function in @code{write-file-hooks} returns non-@code{nil}, it
+If a function in @code{write-file-functions} returns non-@code{nil}, it
is responsible for making a backup file (if that is appropriate).
To do so, execute the following code:
@end example
You might wish to save the file modes value returned by
-@code{backup-buffer} and use that to set the mode bits of the file that
-you write. This is what @code{save-buffer} normally does.
+@code{backup-buffer} and use that (if non-@code{nil}) to set the mode
+bits of the file that you write. This is what @code{save-buffer}
+normally does. @xref{Making Backups,, Making Backup Files}.
+
+The hook functions in @code{write-file-functions} are also responsible for
+encoding the data (if desired): they must choose a suitable coding
+system (@pxref{Lisp and Coding Systems}), perform the encoding
+(@pxref{Explicit Encoding}), and set @code{last-coding-system-used} to
+the coding system that was used (@pxref{Encoding and I/O}).
+
+If you set this hook locally in a buffer, it is assumed to be
+associated with the file or the way the contents of the buffer were
+obtained. Thus the variable is marked as a permanent local, so that
+changing the major mode does not alter a buffer-local value. On the
+other hand, calling @code{set-visited-file-name} will reset it.
+If this is not what you want, you might like to use
+@code{write-contents-functions} instead.
Even though this is not a normal hook, you can use @code{add-hook} and
@code{remove-hook} to manipulate the list. @xref{Hooks}.
@end defvar
@c Emacs 19 feature
-@defvar local-write-file-hooks
-This works just like @code{write-file-hooks}, but it is intended
-to be made local to particular buffers. It's not a good idea to make
-@code{write-file-hooks} local to a buffer---use this variable instead.
-
-The variable is marked as a permanent local, so that changing the major
-mode does not alter a buffer-local value. This is convenient for
-packages that read ``file'' contents in special ways, and set up hooks
-to save the data in a corresponding way.
+@defvar write-contents-functions
+This works just like @code{write-file-functions}, but it is intended
+for hooks that pertain to the buffer's contents, not to the particular
+visited file or its location. Such hooks are usually set up by major
+modes, as buffer-local bindings for this variable. This variable
+automatically becomes buffer-local whenever it is set; switching to a
+new major mode always resets this variable, but calling
+@code{set-visited-file-name} does not.
+
+If any of the functions in this hook returns non-@code{nil}, the file
+is considered already written and the rest are not called and neither
+are the functions in @code{write-file-functions}.
@end defvar
-@c Emacs 19 feature
-@defvar write-contents-hooks
-This works just like @code{write-file-hooks}, but it is intended for
-hooks that pertain to the contents of the file, as opposed to hooks that
-pertain to where the file came from. Typically major mode commands make
-buffer-local bindings for this variable.
-@end defvar
+@defopt before-save-hook
+This normal hook runs before a buffer is saved in its visited file,
+regardless of whether that is done normally or by one of the hooks
+described above. For instance, the @file{copyright.el} program uses
+this hook to make sure the file you are saving has the current year in
+its copyright notice.
+@end defopt
@c Emacs 19 feature
-@defvar after-save-hook
+@defopt after-save-hook
This normal hook runs after a buffer has been saved in its visited file.
-@end defvar
+One use of this hook is in Fast Lock mode; it uses this hook to save the
+highlighting information in a cache file.
+@end defopt
-@defvar file-precious-flag
+@defopt file-precious-flag
If this variable is non-@code{nil}, then @code{save-buffer} protects
against I/O errors while saving by writing the new file to a temporary
name instead of the name it is supposed to have, and then renaming it to
prevents problems such as a lack of disk space from resulting in an
invalid file.
-(This feature worked differently in older Emacs versions.)
+As a side effect, backups are necessarily made by copying. @xref{Rename
+or Copy}. Yet, at the same time, saving a precious file always breaks
+all hard links between the file you save and other file names.
-Some modes set this non-@code{nil} locally in particular buffers.
-@end defvar
+Some modes give this variable a non-@code{nil} buffer-local value
+in particular buffers.
+@end defopt
@defopt require-final-newline
This variable determines whether files may be written out that do
major modes set it to @code{t} in particular buffers.
@end defopt
+ See also the function @code{set-visited-file-name} (@pxref{Buffer File
+Name}).
+
@node Reading from Files
@comment node-name, next, previous, up
@section Reading from Files
@defun insert-file-contents filename &optional visit beg end replace
This function inserts the contents of file @var{filename} into the
-current buffer after point. It returns a list of the absolute file name
+current buffer after point. It returns a list of the absolute file name
and the length of the data inserted. An error is signaled if
@var{filename} is not the name of a file that can be read.
-To set up saved text properties, @code{insert-file-contents} calls the
-functions in the list @code{after-insert-file-functions}. For more
-information, see @ref{Saving Properties}.
+The function @code{insert-file-contents} checks the file contents
+against the defined file formats, and converts the file contents if
+appropriate. @xref{Format Conversion}. It also calls the functions in
+the list @code{after-insert-file-functions}; see @ref{Saving
+Properties}. Normally, one of the functions in the
+@code{after-insert-file-functions} list determines the coding system
+(@pxref{Coding Systems}) used for decoding the file's contents.
If @var{visit} is non-@code{nil}, this function additionally marks the
buffer as unmodified and sets up various fields in the buffer so that it
contents of the file. This is better than simply deleting the buffer
contents and inserting the whole file, because (1) it preserves some
marker positions and (2) it puts less data in the undo list.
+
+It is possible to read a special file (such as a FIFO or an I/O device)
+with @code{insert-file-contents}, as long as @var{replace} and
+@var{visit} are @code{nil}.
+@end defun
+
+@defun insert-file-contents-literally filename &optional visit beg end replace
+This function works like @code{insert-file-contents} except that it does
+not do format decoding (@pxref{Format Conversion}), does not do
+character code conversion (@pxref{Coding Systems}), does not run
+@code{find-file-hook}, does not perform automatic uncompression, and so
+on.
@end defun
If you want to pass a file name to another process so that another
An error is signaled if @var{filename} specifies a nonwritable file,
or a nonexistent file in a directory where files cannot be created.
+
+When called from Lisp, this function is completely equivalent to:
+
+@example
+(write-region start end filename t)
+@end example
@end deffn
-@deffn Command write-region start end filename &optional append visit
+@deffn Command write-region start end filename &optional append visit lockname mustbenew
This function writes the region delimited by @var{start} and @var{end}
in the current buffer into the file specified by @var{filename}.
+If @var{start} is @code{nil}, then the command writes the entire buffer
+contents (@emph{not} just the accessible portion) to the file and
+ignores @var{end}.
+
@c Emacs 19 feature
If @var{start} is a string, then @code{write-region} writes or appends
-that string, rather than text from the buffer.
+that string, rather than text from the buffer. @var{end} is ignored in
+this case.
If @var{append} is non-@code{nil}, then the specified text is appended
-to the existing file contents (if any).
+to the existing file contents (if any). If @var{append} is an
+integer, @code{write-region} seeks to that byte offset from the start
+of the file and writes the data from there.
+
+If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks
+for confirmation if @var{filename} names an existing file. If
+@var{mustbenew} is the symbol @code{excl}, then @code{write-region}
+does not ask for confirmation, but instead it signals an error
+@code{file-already-exists} if the file already exists.
+
+The test for an existing file, when @var{mustbenew} is @code{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.
If @var{visit} is @code{t}, then Emacs establishes an association
between the buffer and the file: the buffer is then visiting that file.
to implement @code{file-precious-flag}; don't use it yourself unless you
really know what you're doing.
-To output information about text properties, @code{write-region} calls
-the functions in the list @code{write-region-annotation-functions}. For
-more information, see @ref{Saving Properties}.
+The optional argument @var{lockname}, if non-@code{nil}, specifies the
+file name to use for purposes of locking and unlocking, overriding
+@var{filename} and @var{visit} for that purpose.
+
+The function @code{write-region} converts the data which it writes to
+the appropriate file formats specified by @code{buffer-file-format}.
+@xref{Format Conversion}. It also calls the functions in the list
+@code{write-region-annotate-functions}; see @ref{Saving Properties}.
-Normally, @code{write-region} displays a message @samp{Wrote file
+Normally, @code{write-region} displays the message @samp{Wrote
@var{filename}} in the echo area. If @var{visit} is neither @code{t}
nor @code{nil} nor a string, then this message is inhibited. This
feature is useful for programs that use files for internal purposes,
-files which the user does not need to know about.
+files that the user does not need to know about.
@end deffn
+@defmac with-temp-file file body@dots{}
+@anchor{Definition of with-temp-file}
+The @code{with-temp-file} macro evaluates the @var{body} forms with a
+temporary buffer as the current buffer; then, at the end, it writes the
+buffer contents into file @var{file}. It kills the temporary buffer
+when finished, restoring the buffer that was current before the
+@code{with-temp-file} form. Then it returns the value of the last form
+in @var{body}.
+
+The current buffer is restored even in case of an abnormal exit via
+@code{throw} or error (@pxref{Nonlocal Exits}).
+
+See also @code{with-temp-buffer} in @ref{Definition of
+with-temp-buffer,, The Current Buffer}.
+@end defmac
+
@node File Locks
@section File Locks
@cindex file locks
- When two users edit the same file at the same time, they are likely to
-interfere with each other. Emacs tries to prevent this situation from
-arising by recording a @dfn{file lock} when a file is being modified.
+ When two users edit the same file at the same time, they are likely
+to interfere with each other. Emacs tries to prevent this situation
+from arising by recording a @dfn{file lock} when a file is being
+modified. (File locks are not implemented on Microsoft systems.)
Emacs can then detect the first attempt to modify a buffer visiting a
file that is locked by another Emacs job, and ask the user what to do.
+The file lock is really a file, a symbolic link with a special name,
+stored in the same directory as the file you are editing.
- File locks do not work properly when multiple machines can share
-file systems, such as with NFS. Perhaps a better file locking system
-will be implemented in the future. When file locks do not work, it is
-possible for two users to make changes simultaneously, but Emacs can
-still warn the user who saves second. Also, the detection of
-modification of a buffer visiting a file changed on disk catches some
-cases of simultaneous editing; see @ref{Modification Time}.
+ When you access files using NFS, there may be a small probability that
+you and another user will both lock the same file ``simultaneously''.
+If this happens, it is possible for the two users to make changes
+simultaneously, but Emacs will still warn the user who saves second.
+Also, the detection of modification of a buffer visiting a file changed
+on disk catches some cases of simultaneous editing; see
+@ref{Modification Time}.
@defun file-locked-p filename
- This function returns @code{nil} if the file @var{filename} is not
-locked by this Emacs process. It returns @code{t} if it is locked by
-this Emacs, and it returns the name of the user who has locked it if it
-is locked by someone else.
+This function returns @code{nil} if the file @var{filename} is not
+locked. It returns @code{t} if it is locked by this Emacs process, and
+it returns the name of the user who has locked it if it is locked by
+some other job.
@example
@group
@end defun
@defun lock-buffer &optional filename
- This function locks the file @var{filename}, if the current buffer is
+This function locks the file @var{filename}, if the current buffer is
modified. The argument @var{filename} defaults to the current buffer's
visited file. Nothing is done if the current buffer is not visiting a
-file, or is not modified.
+file, or is not modified, or if the system does not support locking.
@end defun
@defun unlock-buffer
This function unlocks the file being visited in the current buffer,
if the buffer is modified. If the buffer is not modified, then
the file should not be locked, so this function does nothing. It also
-does nothing if the current buffer is not visiting a file.
+does nothing if the current buffer is not visiting a file, or if the
+system does not support locking.
@end defun
+ File locking is not supported on some systems. On systems that do not
+support it, the functions @code{lock-buffer}, @code{unlock-buffer} and
+@code{file-locked-p} do nothing and return @code{nil}.
+
@defun ask-user-about-lock file other-user
This function is called when the user tries to modify @var{file}, but it
-is locked by another user name @var{other-user}. The value it returns
-determines what happens next:
+is locked by another user named @var{other-user}. The default
+definition of this function asks the user to say what to do. The value
+this function returns determines what Emacs does next:
@itemize @bullet
@item
name of the user who has locked the file.
@end itemize
- The default definition of this function asks the user to choose what
-to do. If you wish, you can replace the @code{ask-user-about-lock}
-function with your own version that decides in another way. The code
+If you wish, you can replace the @code{ask-user-about-lock} function
+with your own version that makes the decision in another way. The code
for its usual definition is in @file{userlock.el}.
@end defun
@node Information about Files
@section Information about Files
- The functions described in this section are similar in as much as
-they all operate on strings which are interpreted as file names. All
-have names that begin with the word @samp{file}. These functions all
+ The functions described in this section all operate on strings that
+designate file names. With a few exceptions, all the functions have
+names that begin with the word @samp{file}. These functions all
return information about actual files or directories, so their
arguments must all exist as actual files or directories unless
otherwise noted.
- Most of the file-oriented functions take a single argument,
-@var{filename}, which must be a string. The file name is expanded using
-@code{expand-file-name}, so @file{~} is handled correctly, as are
-relative file names (including @samp{../}). These functions don't
-recognize environment variable substitutions such as @samp{$HOME}.
-@xref{File Name Expansion}.
-
@menu
* Testing Accessibility:: Is a given file readable? Writable?
* Kinds of Files:: Is it a directory? A symbolic link?
* Truenames:: Eliminating symbolic links from a file name.
* File Attributes:: How large is it? Any other names? Etc.
+* Locating Files:: How to find a file in standard places.
@end menu
@node Testing Accessibility
@cindex accessibility of a file
@cindex file accessibility
- These functions test for permission to access a file in specific ways.
+ These functions test for permission to access a file in specific
+ways. Unless explicitly stated otherwise, they recursively follow
+symbolic links for their file name arguments, at all levels (at the
+level of the file itself and at all levels of parent directories).
@defun file-exists-p filename
This function returns @code{t} if a file named @var{filename} appears
to exist. This does not mean you can necessarily read the file, only
-that you can find out its attributes. (On Unix, this is true if the
-file exists and you have execute permission on the containing
-directories, regardless of the protection of the file itself.)
+that you can find out its attributes. (On Unix and GNU/Linux, this is
+true if the file exists and you have execute permission on the
+containing directories, regardless of the protection of the file
+itself.)
If the file does not exist, or if fascist access control policies
prevent you from finding the attributes of the file, this function
returns @code{nil}.
+
+Directories are files, so @code{file-exists-p} returns @code{t} when
+given a directory name. However, symbolic links are treated
+specially; @code{file-exists-p} returns @code{t} for a symbolic link
+name only if the target file exists.
@end defun
@defun file-readable-p filename
@c Emacs 19 feature
@defun file-executable-p filename
This function returns @code{t} if a file named @var{filename} exists and
-you can execute it. It returns @code{nil} otherwise. If the file is a
-directory, execute permission means you can check the existence and
-attributes of files inside the directory, and open those files if their
-modes permit.
+you can execute it. It returns @code{nil} otherwise. On Unix and
+GNU/Linux, if the file is a directory, execute permission means you can
+check the existence and attributes of files inside the directory, and
+open those files if their modes permit.
@end defun
@defun file-writable-p filename
-This function returns @code{t} if the file @var{filename} can be written or
-created by you. It is writable if the file exists and you can write it.
-It is creatable if the file does not exist, but the specified directory
-does exist and you can write in that directory. @code{file-writable-p}
-returns @code{nil} otherwise.
+This function returns @code{t} if the file @var{filename} can be written
+or created by you, and @code{nil} otherwise. A file is writable if the
+file exists and you can write it. It is creatable if it does not exist,
+but the specified directory does exist and you can write in that
+directory.
In the third example below, @file{foo} is not writable because the
parent directory does not exist, even though the user could create such
@c Emacs 19 feature
@defun file-accessible-directory-p dirname
This function returns @code{t} if you have permission to open existing
-files in directory @var{dirname}; otherwise (and if there is no such
-directory), it returns @code{nil}. The value of @var{dirname} may be
-either a directory name or the file name of a directory.
+files in the directory whose name as a file is @var{dirname};
+otherwise (or if there is no such directory), it returns @code{nil}.
+The value of @var{dirname} may be either a directory name (such as
+@file{/foo/}) or the file name of a file which is a directory
+(such as @file{/foo}, without the final slash).
Example: after the following,
give an error.
@end defun
+@defun access-file filename string
+This function opens file @var{filename} for reading, then closes it and
+returns @code{nil}. However, if the open fails, it signals an error
+using @var{string} as the error message text.
+@end defun
+
+@defun file-ownership-preserved-p filename
+This function returns @code{t} if deleting the file @var{filename} and
+then creating it anew would keep the file's owner unchanged. It also
+returns @code{t} for nonexistent files.
+
+If @var{filename} is a symbolic link, then, unlike the other functions
+discussed here, @code{file-ownership-preserved-p} does @emph{not}
+replace @var{filename} with its target. However, it does recursively
+follow symbolic links at all levels of parent directories.
+@end defun
+
@defun file-newer-than-file-p filename1 filename2
@cindex file age
@cindex file modification time
-This functions returns @code{t} if the file @var{filename1} is
+This function returns @code{t} if the file @var{filename1} is
newer than file @var{filename2}. If @var{filename1} does not
-exist, it returns @code{nil}. If @var{filename2} does not exist,
-it returns @code{t}.
+exist, it returns @code{nil}. If @var{filename1} does exist, but
+@var{filename2} does not, it returns @code{t}.
-In the following example, assume that the file @file{aug-19} was
-written on the 19th, and @file{aug-20} was written on the 20th. The
-file @file{no-file} doesn't exist at all.
+In the following example, assume that the file @file{aug-19} was written
+on the 19th, @file{aug-20} was written on the 20th, and the file
+@file{no-file} doesn't exist at all.
@example
@group
@comment node-name, next, previous, up
@subsection Distinguishing Kinds of Files
- This section describes how to distinguish directories and symbolic
-links from ordinary files.
+ This section describes how to distinguish various kinds of files, such
+as directories, symbolic links, and ordinary files.
@defun file-symlink-p filename
@cindex file symbolic links
-If the file @var{filename} is a symbolic link, the @code{file-symlink-p}
-function returns the file name to which it is linked. This may be the
-name of a text file, a directory, or even another symbolic link, or of
-no file at all.
+If the file @var{filename} is a symbolic link, the
+@code{file-symlink-p} function returns the (non-recursive) link target
+as a string. (Determining the file name that the link points to from
+the target is nontrivial.) First, this function recursively follows
+symbolic links at all levels of parent directories.
If the file @var{filename} is not a symbolic link (or there is no such file),
-@code{file-symlink-p} returns @code{nil}.
+@code{file-symlink-p} returns @code{nil}.
@example
@group
@c !!! file-symlink-p: should show output of ls -l for comparison
@end defun
+The next two functions recursively follow symbolic links at
+all levels for @var{filename}.
+
@defun file-directory-p filename
This function returns @code{t} if @var{filename} is the name of an
existing directory, @code{nil} otherwise.
@end example
@end defun
+@defun file-regular-p filename
+This function returns @code{t} if the file @var{filename} exists and is
+a regular file (not a directory, named pipe, terminal, or
+other I/O device).
+@end defun
+
@node Truenames
@subsection Truenames
@cindex truename (of file)
@c Emacs 19 features
The @dfn{truename} of a file is the name that you get by following
-symbolic links until none remain, then expanding to get rid of @samp{.}
-and @samp{..} as components. Strictly speaking, a file need not have a
+symbolic links at all levels until none remain, then simplifying away
+@samp{.}@: and @samp{..}@: appearing as name components. This results
+in a sort of canonical name for the file. A file does not always have a
unique truename; the number of distinct truenames a file has is equal to
the number of hard links to the file. However, truenames are useful
because they eliminate symbolic links as a cause of name variation.
@defun file-truename filename
-The function @code{file-truename} returns the true name of the file
-@var{filename}. This is the name that you get by following symbolic
-links until none remain. The argument must be an absolute file name.
+The function @code{file-truename} returns the truename of the file
+@var{filename}. The argument must be an absolute file name.
+
+This function does not expand environment variables. Only
+@code{substitute-in-file-name} does that. @xref{Definition of
+substitute-in-file-name}.
+
+If you may need to follow symbolic links preceding @samp{..}@:
+appearing as a name component, you should make sure to call
+@code{file-truename} without prior direct or indirect calls to
+@code{expand-file-name}, as otherwise the file name component
+immediately preceding @samp{..} will be ``simplified away'' before
+@code{file-truename} is called. To eliminate the need for a call to
+@code{expand-file-name}, @code{file-truename} handles @samp{~} in the
+same way that @code{expand-file-name} does. @xref{File Name
+Expansion,, Functions that Expand Filenames}.
+@end defun
+
+@defun file-chase-links filename &optional limit
+This function follows symbolic links, starting with @var{filename},
+until it finds a file name which is not the name of a symbolic link.
+Then it returns that file name. This function does @emph{not} follow
+symbolic links at the level of parent directories.
+
+If you specify a number for @var{limit}, then after chasing through
+that many links, the function just returns what it has even if that is
+still a symbolic link.
@end defun
+ To illustrate the difference between @code{file-chase-links} and
+@code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to
+the directory @file{/home/foo}, and @file{/home/foo/hello} is an
+ordinary file (or at least, not a symbolic link) or nonexistent. Then
+we would have:
+
+@example
+(file-chase-links "/usr/foo/hello")
+ ;; @r{This does not follow the links in the parent directories.}
+ @result{} "/usr/foo/hello"
+(file-truename "/usr/foo/hello")
+ ;; @r{Assuming that @file{/home} is not a symbolic link.}
+ @result{} "/home/foo/hello"
+@end example
+
@xref{Buffer File Name}, for related information.
@node File Attributes
This function returns the mode bits of @var{filename}, as an integer.
The mode bits are also called the file permissions, and they specify
access control in the usual Unix fashion. If the low-order bit is 1,
-then the file is executable by all users, if the second lowest-order bit
+then the file is executable by all users, if the second-lowest-order bit
is 1, then the file is writable by all users, etc.
The highest value returnable is 4095 (7777 octal), meaning that
-everyone has read, write, and execute permission, that the @sc{suid} bit
+everyone has read, write, and execute permission, that the @acronym{SUID} bit
is set for both others and group, and that the sticky bit is set.
+If @var{filename} does not exist, @code{file-modes} returns @code{nil}.
+
+This function recursively follows symbolic links at all levels.
+
@example
@group
(file-modes "~/junk/diffs")
@end example
@end defun
+If the @var{filename} argument to the next two functions is a symbolic
+link, then these function do @emph{not} replace it with its target.
+However, they both recursively follow symbolic links at all levels of
+parent directories.
+
@defun file-nlinks filename
This functions returns the number of names (i.e., hard links) that
file @var{filename} has. If the file does not exist, then this function
@end example
@end defun
-@defun file-attributes filename
+@defun file-attributes filename &optional id-format
+@anchor{Definition of file-attributes}
This function returns a list of attributes of file @var{filename}. If
the specified file cannot be opened, it returns @code{nil}.
+The optional parameter @var{id-format} specifies the preferred format
+of attributes @acronym{UID} and @acronym{GID} (see below)---the
+valid values are @code{'string} and @code{'integer}. The latter is
+the default, but we plan to change that, so you should specify a
+non-@code{nil} value for @var{id-format} if you use the returned
+@acronym{UID} or @acronym{GID}.
The elements of the list, in order, are:
@item
The number of names the file has. Alternate names, also known as hard
links, can be created by using the @code{add-name-to-file} function
-(@pxref{Changing File Attributes}).
+(@pxref{Changing Files}).
@item
-The file's @sc{uid}.
+The file's @acronym{UID} as a string or an integer. If a string
+value cannot be looked up, the integer value is returned.
@item
-The file's @sc{gid}.
+The file's @acronym{GID} likewise.
@item
The time of last access, as a list of two integers.
The time of last status change as a list of two integers (as above).
@item
-The size of the file in bytes.
+The size of the file in bytes. If the size is too large to fit in a
+Lisp integer, this is a floating point number.
@item
-The file's modes, as a string of ten letters or dashes
+The file's modes, as a string of ten letters or dashes,
as in @samp{ls -l}.
@item
-@code{t} if the file's @sc{gid} would change if file were
+@code{t} if the file's @acronym{GID} would change if file were
deleted and recreated; @code{nil} otherwise.
@item
-The file's inode number.
+The file's inode number. If possible, this is an integer. If the inode
+number is too large to be represented as an integer in Emacs Lisp, then
+the value has the form @code{(@var{high} . @var{low})}, where @var{low}
+holds the low 16 bits.
@item
-The file system number of the file system that the file is in. This
-element together with the file's inode number, give enough information
-to distinguish any two files on the system---no two files can have the
-same values for both of these numbers.
+The file system number of the file system that the file is in.
+Depending on the magnitude of the value, this can be either an integer
+or a cons cell, in the same manner as the inode number. This element
+and the file's inode number together give enough information to
+distinguish any two files on the system---no two files can have the same
+values for both of these numbers.
@end enumerate
For example, here are the file attributes for @file{files.texi}:
@example
@group
-(file-attributes "files.texi")
- @result{} (nil
- 1
- 2235
- 75
- (8489 20284)
- (8489 20284)
+(file-attributes "files.texi" 'string)
+ @result{} (nil 1 "lh" "users"
+ (8489 20284)
+ (8489 20284)
(8489 20285)
- 14906
- "-rw-rw-rw-"
- nil
- 129500
- -32252)
+ 14906 "-rw-rw-rw-"
+ nil 129500 -32252)
@end group
@end example
has only one name (the name @file{files.texi} in the current default
directory).
-@item 2235
-is owned by the user with @sc{uid} 2235.
+@item "lh"
+is owned by the user with name "lh".
-@item 75
-is in the group with @sc{gid} 75.
+@item "users"
+is in the group with name "users".
@item (8489 20284)
-was last accessed on Aug 19 00:09. Unfortunately, you cannot convert
-this number into a time string in Emacs.
+was last accessed on Aug 19 00:09.
@item (8489 20284)
was last modified on Aug 19 00:09.
last had its inode changed on Aug 19 00:09.
@item 14906
-is 14906 characters long.
+is 14906 bytes long. (It may not contain 14906 characters, though,
+if some of the bytes belong to multibyte sequences.)
@item "-rw-rw-rw-"
has a mode of read and write access for the owner, group, and world.
@item nil
-would retain the same @sc{gid} if it were recreated.
+would retain the same @acronym{GID} if it were recreated.
@item 129500
has an inode number of 129500.
@end table
@end defun
-@node Changing File Attributes
+@node Locating Files
+@subsection How to Locate Files in Standard Places
+@cindex locate files
+@cindex find files
+
+ This section explains how to search for a file in a list of
+directories. One example is when you need to look for a program's
+executable file, e.g., to find out whether a given program is
+installed on the user's system. Another example is the search for
+Lisp libraries (@pxref{Library Search}). Such searches generally need
+to try various possible file name extensions, in addition to various
+possible directories. Emacs provides a function for such a
+generalized search for a file.
+
+@defun locate-file filename path &optional suffixes predicate
+This function searches for a file whose name is @var{filename} in a
+list of directories given by @var{path}, trying the suffixes in
+@var{suffixes}. If it finds such a file, it returns the full
+@dfn{absolute file name} of the file (@pxref{Relative File Names});
+otherwise it returns @code{nil}.
+
+The optional argument @var{suffixes} gives the list of file-name
+suffixes to append to @var{filename} when searching.
+@code{locate-file} tries each possible directory with each of these
+suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there
+are no suffixes, and @var{filename} is used only as-is. Typical
+values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess
+Creation, exec-suffixes}), @code{load-suffixes},
+@code{load-file-rep-suffixes} and the return value of the function
+@code{get-load-suffixes} (@pxref{Load Suffixes}).
+
+Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess
+Creation, exec-path}) when looking for executable programs or
+@code{load-path} (@pxref{Library Search, load-path}) when looking for
+Lisp files. If @var{filename} is absolute, @var{path} has no effect,
+but the suffixes in @var{suffixes} are still tried.
+
+The optional argument @var{predicate}, if non-@code{nil}, specifies
+the predicate function to use for testing whether a candidate file is
+suitable. The predicate function is passed the candidate file name as
+its single argument. If @var{predicate} is @code{nil} or unspecified,
+@code{locate-file} uses @code{file-readable-p} as the default
+predicate. Useful non-default predicates include
+@code{file-executable-p}, @code{file-directory-p}, and other
+predicates described in @ref{Kinds of Files}.
+
+For compatibility, @var{predicate} can also be one of the symbols
+@code{executable}, @code{readable}, @code{writable}, @code{exists}, or
+a list of one or more of these symbols.
+@end defun
+
+@cindex find executable program
+@defun executable-find program
+This function searches for the executable file of the named
+@var{program} and returns the full absolute name of the executable,
+including its file-name extensions, if any. It returns @code{nil} if
+the file is not found. The functions searches in all the directories
+in @code{exec-path} and tries all the file-name extensions in
+@code{exec-suffixes}.
+@end defun
+
+@node Changing Files
@section Changing File Names and Attributes
@cindex renaming files
@cindex copying files
is any other value.
@end itemize
-@defun add-name-to-file oldname newname &optional ok-if-already-exists
+The next four commands all recursively follow symbolic links at all
+levels of parent directories for their first argument, but, if that
+argument is itself a symbolic link, then only @code{copy-file}
+replaces it with its (recursive) target.
+
+@deffn Command add-name-to-file oldname newname &optional ok-if-already-exists
@cindex file with multiple names
@cindex file hard link
This function gives the file named @var{oldname} the additional name
@example
@group
-% ls -l fo*
--rw-rw-rw- 1 rms 29 Aug 18 20:32 foo
--rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
+% ls -li fo*
+81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo
+84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
@end group
@end example
-Then we evaluate the form @code{(add-name-to-file "~/lewis/foo"
-"~/lewis/foo2")}. Again we list the files. This shows two names,
-@file{foo} and @file{foo2}.
+Now we create a hard link, by calling @code{add-name-to-file}, then list
+the files again. This shows two names for one file, @file{foo} and
+@file{foo2}.
@example
@group
-(add-name-to-file "~/lewis/foo1" "~/lewis/foo2")
+(add-name-to-file "foo" "foo2")
@result{} nil
@end group
@group
-% ls -l fo*
--rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
--rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
--rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
+% ls -li fo*
+81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
+81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
+84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
@end group
@end example
-@c !!! Check whether this set of examples is consistent. --rjc 15mar92
- Finally, we evaluate the following:
+Finally, we evaluate the following:
@example
-(add-name-to-file "~/lewis/foo" "~/lewis/foo3" t)
+(add-name-to-file "foo" "foo3" t)
@end example
@noindent
@example
@group
-(add-name-to-file "~/lewis/foo1" "~/lewis/foo3")
+(add-name-to-file "foo1" "foo3")
@result{} nil
@end group
@group
-% ls -l fo*
--rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
--rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
--rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
+% ls -li fo*
+81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
+81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
+81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
@end group
@end example
- This function is meaningless on VMS, where multiple names for one file
-are not allowed.
+This function is meaningless on operating systems where multiple names
+for one file are not allowed. Some systems implement multiple names
+by copying the file instead.
- See also @code{file-nlinks} in @ref{File Attributes}.
-@end defun
+See also @code{file-nlinks} in @ref{File Attributes}.
+@end deffn
@deffn Command rename-file filename newname &optional ok-if-already-exists
This command renames the file @var{filename} as @var{newname}.
continues to have those names. In fact, adding the name @var{newname}
with @code{add-name-to-file} and then deleting @var{filename} has the
same effect as renaming, aside from momentary intermediate states.
-
-In an interactive call, this function prompts for @var{filename} and
-@var{newname} in the minibuffer; also, it requests confirmation if
-@var{newname} already exists.
@end deffn
-@deffn Command copy-file oldname newname &optional ok-if-exists time
+@deffn Command copy-file oldname newname &optional ok-if-exists time mustbenew
This command copies the file @var{oldname} to @var{newname}. An
-error is signaled if @var{oldname} does not exist.
+error is signaled if @var{oldname} does not exist. If @var{newname}
+names a directory, it copies @var{oldname} into that directory,
+preserving its final name component.
-If @var{time} is non-@code{nil}, then this functions gives the new
-file the same last-modified time that the old one has. (This works on
-only some operating systems.)
+If @var{time} is non-@code{nil}, then this function gives the new file
+the same last-modified time that the old one has. (This works on only
+some operating systems.) If setting the time gets an error,
+@code{copy-file} signals a @code{file-date-error} error.
-In an interactive call, this function prompts for @var{filename} and
-@var{newname} in the minibuffer; also, it requests confirmation if
-@var{newname} already exists.
-@end deffn
+This function copies the file modes, too.
-@deffn Command delete-file filename
-@pindex rm
-This command deletes the file @var{filename}, like the shell command
-@samp{rm @var{filename}}. If the file has multiple names, it continues
-to exist under the other names.
-
-A suitable kind of @code{file-error} error is signaled if the file
-does not exist, or is not deletable. (On Unix, a file is deletable if
-its directory is writable.)
+In an interactive call, a prefix argument specifies a non-@code{nil}
+value for @var{time}.
-See also @code{delete-directory} in @ref{Create/Delete Dirs}.
+The argument @var{mustbenew} controls whether an existing file can be
+overwritten. It works like the similarly-named argument of
+@code{write-region} (@pxref{Writing to Files, mustbenew}).
@end deffn
@deffn Command make-symbolic-link filename newname &optional ok-if-exists
@var{newname}. This is like the shell command @samp{ln -s
@var{filename} @var{newname}}.
-In an interactive call, @var{filename} and @var{newname} are read in the
-minibuffer; it requests confirmation if the file @var{newname} already
-exists.
+This function is not available on systems that don't support symbolic
+links.
+@end deffn
+
+@deffn Command delete-file filename
+@pindex rm
+This command deletes the file @var{filename}, like the shell command
+@samp{rm @var{filename}}. If the file has multiple names, it continues
+to exist under the other names.
+
+A suitable kind of @code{file-error} error is signaled if the file does
+not exist, or is not deletable. (On Unix and GNU/Linux, a file is
+deletable if its directory is writable.)
+
+If @var{filename} is a symbolic link, @code{delete-file} does not
+replace it with its target, but it does follow symbolic links at all
+levels of parent directories.
+
+See also @code{delete-directory} in @ref{Create/Delete Dirs}.
@end deffn
@defun define-logical-name varname string
-This function defines the logical name @var{name} to have the value
+This function defines the logical name @var{varname} to have the value
@var{string}. It is available only on VMS.
@end defun
@defun set-file-modes filename mode
-This function sets mode bits of @var{filename} to @var{mode} (which must
-be an integer). Only the 12 low bits of @var{mode} are used.
+This function sets mode bits of @var{filename} to @var{mode} (which
+must be an integer). Only the low 12 bits of @var{mode} are used.
+This function recursively follows symbolic links at all levels for
+@var{filename}.
@end defun
@c Emacs 19 feature
@defun set-default-file-modes mode
+@cindex umask
This function sets the default file protection for new files created by
Emacs and its subprocesses. Every file created with Emacs initially has
-this protection. On Unix, the default protection is the bitwise
-complement of the ``umask'' value.
+this protection, or a subset of it (@code{write-region} will not give a
+file execute permission even if the default file protection allows
+execute permission). On Unix and GNU/Linux, the default protection is
+the bitwise complement of the ``umask'' value.
+
+The argument @var{mode} must be an integer. On most systems, only the
+low 9 bits of @var{mode} are meaningful. You can use the Lisp construct
+for octal character codes to enter @var{mode}; for example,
-The argument @var{mode} must be an integer. Only the 9 low bits of
-@var{mode} are used.
+@example
+(set-default-file-modes ?\644)
+@end example
Saving a modified version of an existing file does not count as creating
-the file; it does not change the file's mode, and does not use the
-default file protection.
+the file; it preserves the existing file's mode, whatever that is. So
+the default file protection has no effect.
@end defun
@defun default-file-modes
This function returns the current default protection value.
@end defun
+@defun set-file-times filename &optional time
+This function sets the access and modification times of @var{filename}
+to @var{time}. The return value is @code{t} if the times are successfully
+set, otherwise it is @code{nil}. @var{time} defaults to the current
+time and must be in the format returned by @code{current-time}
+(@pxref{Time of Day}).
+@end defun
+
@cindex MS-DOS and file modes
@cindex file modes and MS-DOS
On MS-DOS, there is no such thing as an ``executable'' file mode bit.
-So Emacs considers a file executable if its name ends in @samp{.com},
-@samp{.bat} or @samp{.exe}. This is reflected in the values returned
-by @code{file-modes} and @code{file-attributes}.
+So Emacs considers a file executable if its name ends in one of the
+standard executable extensions, such as @file{.com}, @file{.bat},
+@file{.exe}, and some others. Files that begin with the Unix-standard
+@samp{#!} signature, such as shell and Perl scripts, are also considered
+as executable files. This is reflected in the values returned by
+@code{file-modes} and @code{file-attributes}. Directories are also
+reported with executable bit set, for compatibility with Unix.
@node File Names
@section File Names
operate on a file all expect a file name argument.
In addition to operating on files themselves, Emacs Lisp programs
-often need to operate on the names; i.e., to take them apart and to use
+often need to operate on file names; i.e., to take them apart and to use
part of a name to construct related file names. This section describes
how to manipulate file names.
can operate on file names that do not refer to an existing file or
directory.
- On VMS, all these functions understand both VMS file name syntax and
-Unix syntax. This is so that all the standard Lisp libraries can
-specify file names in Unix syntax and work properly on VMS without
-change. On MS-DOS, these functions understand MS-DOS file name syntax
-as well as Unix syntax.
+ On MS-DOS and MS-Windows, these functions (like the function that
+actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
+where backslashes separate the components, as well as Unix syntax; but
+they always return Unix syntax. On VMS, these functions (and the ones
+that operate on files) understand both VMS file-name syntax and Unix
+syntax. This enables Lisp programs to specify file names in Unix syntax
+and work properly on all systems without change.
@menu
* File Name Components:: The directory part of a file name, and the rest.
+* Relative File Names:: Some file names are relative to a current directory.
* Directory Names:: A directory's name as a directory
is different from its name as a file.
-* Relative File Names:: Some file names are relative to a current directory.
* File Name Expansion:: Converting relative file names to absolute ones.
* Unique File Names:: Generating names for temporary files.
* File Name Completion:: Finding the completions for a given file name.
+* Standard File Names:: If your package uses a fixed file name,
+ how to handle various operating systems simply.
@end menu
@node File Name Components
@cindex version number (in file name)
The operating system groups files into directories. To specify a
-file, you must specify the directory, and the file's name in that
-directory. Therefore, a file name in Emacs is considered to have two
-main parts: the @dfn{directory name} part, and the @dfn{nondirectory}
-part (or @dfn{file name within the directory}). Either part may be
-empty. Concatenating these two parts reproduces the original file name.
+file, you must specify the directory and the file's name within that
+directory. Therefore, Emacs considers a file name as having two main
+parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
+(or @dfn{file name within the directory}). Either part may be empty.
+Concatenating these two parts reproduces the original file name.
- On Unix, the directory part is everything up to and including the last
-slash; the nondirectory part is the rest. The rules in VMS syntax are
-complicated.
+ On most systems, the directory part is everything up to and including
+the last slash (backslash is also allowed in input on MS-DOS or
+MS-Windows); the nondirectory part is the rest. The rules in VMS syntax
+are complicated.
For some purposes, the nondirectory part is further subdivided into
-the name proper and the @dfn{version number}. On Unix, only backup
-files have version numbers in their names; on VMS, every file has a
-version number, but most of the time the file name actually used in
-Emacs omits the version number. Version numbers are found mostly in
-directory lists.
+the name proper and the @dfn{version number}. On most systems, only
+backup files have version numbers in their names. On VMS, every file
+has a version number, but most of the time the file name actually used
+in Emacs omits the version number, so that version numbers in Emacs are
+found mostly in directory lists.
@defun file-name-directory filename
- This function returns the directory part of @var{filename} (or
-@code{nil} if @var{filename} does not include a directory part). On
-Unix, the function returns a string ending in a slash. On VMS, it
+This function returns the directory part of @var{filename}, as a
+directory name (@pxref{Directory Names}), or @code{nil} if
+@var{filename} does not include a directory part.
+
+On GNU and Unix systems, a string returned by this function always
+ends in a slash. On MSDOS it can also end in a colon. On VMS, it
returns a string ending in one of the three characters @samp{:},
@samp{]}, or @samp{>}.
@end defun
@defun file-name-nondirectory filename
- This function returns the nondirectory part of @var{filename}.
+This function returns the nondirectory part of @var{filename}.
@example
@group
@result{} "foo"
@end group
@group
+(file-name-nondirectory "lewis/")
+ @result{} ""
+@end group
+@group
;; @r{The following example is accurate only on VMS.}
(file-name-nondirectory "[X]FOO.TMP")
@result{} "FOO.TMP"
@end example
@end defun
-@defun file-name-sans-versions filename
- This function returns @var{filename} without any file version numbers,
-backup version numbers, or trailing tildes.
+@defun file-name-sans-versions filename &optional keep-backup-version
+This function returns @var{filename} with any file version numbers,
+backup version numbers, or trailing tildes discarded.
+
+If @var{keep-backup-version} is non-@code{nil}, then true file version
+numbers understood as such by the file system are discarded from the
+return value, but backup version numbers are kept.
@example
@group
@end example
@end defun
+@defun file-name-extension filename &optional period
+This function returns @var{filename}'s final ``extension'', if any,
+after applying @code{file-name-sans-versions} to remove any
+version/backup part. The extension, in a file name, is the part that
+starts with the last @samp{.} in the last name component (minus
+any version/backup part).
+
+This function returns @code{nil} for extensionless file names such as
+@file{foo}. It returns @code{""} for null extensions, as in
+@file{foo.}. If the last component of a file name begins with a
+@samp{.}, that @samp{.} doesn't count as the beginning of an
+extension. Thus, @file{.emacs}'s ``extension'' is @code{nil}, not
+@samp{.emacs}.
+
+If @var{period} is non-@code{nil}, then the returned value includes
+the period that delimits the extension, and if @var{filename} has no
+extension, the value is @code{""}.
+@end defun
+
+@defun file-name-sans-extension filename
+This function returns @var{filename} minus its extension, if any. The
+version/backup part, if present, is only removed if the file has an
+extension. For example,
+
+@example
+(file-name-sans-extension "foo.lose.c")
+ @result{} "foo.lose"
+(file-name-sans-extension "big.hack/foo")
+ @result{} "big.hack/foo"
+(file-name-sans-extension "/my/home/.emacs")
+ @result{} "/my/home/.emacs"
+(file-name-sans-extension "/my/home/.emacs.el")
+ @result{} "/my/home/.emacs"
+(file-name-sans-extension "~/foo.el.~3~")
+ @result{} "~/foo"
+(file-name-sans-extension "~/foo.~3~")
+ @result{} "~/foo.~3~"
+@end example
+
+Note that the @samp{.~3~} in the two last examples is the backup part,
+not an extension.
+@end defun
+
+@ignore
+Andrew Innes says that this
+
+@c @defvar directory-sep-char
+@c @tindex directory-sep-char
+This variable holds the character that Emacs normally uses to separate
+file name components. The default value is @code{?/}, but on MS-Windows
+you can set it to @code{?\\}; then the functions that transform file names
+use backslashes in their output.
+
+File names using backslashes work as input to Lisp primitives even on
+MS-DOS and MS-Windows, even if @code{directory-sep-char} has its default
+value of @code{?/}.
+@end defvar
+@end ignore
+
+@node Relative File Names
+@subsection Absolute and Relative File Names
+@cindex absolute file name
+@cindex relative file name
+
+ All the directories in the file system form a tree starting at the
+root directory. A file name can specify all the directory names
+starting from the root of the tree; then it is called an @dfn{absolute}
+file name. Or it can specify the position of the file in the tree
+relative to a default directory; then it is called a @dfn{relative} file
+name. On Unix and GNU/Linux, an absolute file name starts with a slash
+or a tilde (@samp{~}), and a relative one does not. On MS-DOS and
+MS-Windows, an absolute file name starts with a slash or a backslash, or
+with a drive specification @samp{@var{x}:/}, where @var{x} is the
+@dfn{drive letter}. The rules on VMS are complicated.
+
+@defun file-name-absolute-p filename
+This function returns @code{t} if file @var{filename} is an absolute
+file name, @code{nil} otherwise. On VMS, this function understands both
+Unix syntax and VMS syntax.
+
+@example
+@group
+(file-name-absolute-p "~rms/foo")
+ @result{} t
+@end group
+@group
+(file-name-absolute-p "rms/foo")
+ @result{} nil
+@end group
+@group
+(file-name-absolute-p "/user/rms/foo")
+ @result{} t
+@end group
+@end example
+@end defun
+
+ Given a possibly relative file name, you can convert it to an
+absolute name using @code{expand-file-name} (@pxref{File Name
+Expansion}). This function converts absolute file names to relative
+names:
+
+@defun file-relative-name filename &optional directory
+This function tries to return a relative name that is equivalent to
+@var{filename}, assuming the result will be interpreted relative to
+@var{directory} (an absolute directory name or directory file name).
+If @var{directory} is omitted or @code{nil}, it defaults to the
+current buffer's default directory.
+
+On some operating systems, an absolute file name begins with a device
+name. On such systems, @var{filename} has no relative equivalent based
+on @var{directory} if they start with two different device names. In
+this case, @code{file-relative-name} returns @var{filename} in absolute
+form.
+
+@example
+(file-relative-name "/foo/bar" "/foo/")
+ @result{} "bar"
+(file-relative-name "/foo/bar" "/hack/")
+ @result{} "../foo/bar"
+@end example
+@end defun
+
@node Directory Names
@comment node-name, next, previous, up
@subsection Directory Names
@cindex directory name
@cindex file name of directory
- A @dfn{directory name} is the name of a directory. A directory is a
-kind of file, and it has a file name, which is related to the directory
-name but not identical to it. (This is not quite the same as the usual
-Unix terminology.) These two different names for the same entity are
-related by a syntactic transformation. On Unix, this is simple: a
-directory name ends in a slash, whereas the directory's name as a file
-lacks that slash. On VMS, the relationship is more complicated.
+ A @dfn{directory name} is the name of a directory. A directory is
+actually a kind of file, so it has a file name, which is related to
+the directory name but not identical to it. (This is not quite the
+same as the usual Unix terminology.) These two different names for
+the same entity are related by a syntactic transformation. On GNU and
+Unix systems, this is simple: a directory name ends in a slash,
+whereas the directory's name as a file lacks that slash. On MSDOS and
+VMS, the relationship is more complicated.
The difference between a directory name and its name as a file is
subtle but crucial. When an Emacs variable or function argument is
described as being a directory name, a file name of a directory is not
-acceptable.
+acceptable. When @code{file-name-directory} returns a string, that is
+always a directory name.
- These two functions convert between directory names and file names.
-They do nothing special with environment variable substitutions such as
-@samp{$HOME}, and the constructs @samp{~}, and @samp{..}.
+ The following two functions convert between directory names and file
+names. They do nothing special with environment variable substitutions
+such as @samp{$HOME}, and the constructs @samp{~}, @samp{.} and @samp{..}.
@defun file-name-as-directory filename
This function returns a string representing @var{filename} in a form
-that the operating system will interpret as the name of a directory. In
-Unix, this means appending a slash to the string. On VMS, the function
-converts a string of the form @file{[X]Y.DIR.1} to the form
-@file{[X.Y]}.
+that the operating system will interpret as the name of a directory. On
+most systems, this means appending a slash to the string (if it does not
+already end in one). On VMS, the function converts a string of the form
+@file{[X]Y.DIR.1} to the form @file{[X.Y]}.
@example
@group
@end defun
@defun directory-file-name dirname
-This function returns a string representing @var{dirname} in a form
-that the operating system will interpret as the name of a file. On
-Unix, this means removing a final slash from the string. On VMS, the
-function converts a string of the form @file{[X.Y]} to
-@file{[X]Y.DIR.1}.
+This function returns a string representing @var{dirname} in a form that
+the operating system will interpret as the name of a file. On most
+systems, this means removing the final slash (or backslash) from the
+string. On VMS, the function converts a string of the form @file{[X.Y]}
+to @file{[X]Y.DIR.1}.
@example
@group
@end example
@end defun
+ Given a directory name, you can combine it with a relative file name
+using @code{concat}:
+
+@example
+(concat @var{dirname} @var{relfile})
+@end example
+
+@noindent
+Be sure to verify that the file name is relative before doing that.
+If you use an absolute file name, the results could be syntactically
+invalid or refer to the wrong file.
+
+ If you want to use a directory file name in making such a
+combination, you must first convert it to a directory name using
+@code{file-name-as-directory}:
+
+@example
+(concat (file-name-as-directory @var{dirfile}) @var{relfile})
+@end example
+
+@noindent
+Don't try concatenating a slash by hand, as in
+
+@example
+;;; @r{Wrong!}
+(concat @var{dirfile} "/" @var{relfile})
+@end example
+
+@noindent
+because this is not portable. Always use
+@code{file-name-as-directory}.
+
@cindex directory name abbreviation
Directory name abbreviations are useful for directories that are
normally accessed through symbolic links. Sometimes the users recognize
@code{(@var{from} . @var{to})}, and says to replace @var{from} with
@var{to} when it appears in a directory name. The @var{from} string is
actually a regular expression; it should always start with @samp{^}.
-The function @code{abbreviate-file-name} performs these substitutions.
+The @var{to} string should be an ordinary absolute directory name. Do
+not use @samp{~} to stand for a home directory in that string. The
+function @code{abbreviate-file-name} performs these substitutions.
You can set this variable in @file{site-init.el} to describe the
abbreviations appropriate for your site.
To convert a directory name to its abbreviation, use this
function:
-@defun abbreviate-file-name dirname
+@defun abbreviate-file-name filename
+@anchor{Definition of abbreviate-file-name}
This function applies abbreviations from @code{directory-abbrev-alist}
to its argument, and substitutes @samp{~} for the user's home
-directory.
-@end defun
-
-@node Relative File Names
-@subsection Absolute and Relative File Names
-@cindex absolute file name
-@cindex relative file name
-
- All the directories in the file system form a tree starting at the
-root directory. A file name can specify all the directory names
-starting from the root of the tree; then it is called an @dfn{absolute}
-file name. Or it can specify the position of the file in the tree
-relative to a default directory; then it is called a @dfn{relative}
-file name. On Unix, an absolute file name starts with a slash or a
-tilde (@samp{~}), and a relative one does not. The rules on VMS are
-complicated.
-
-@defun file-name-absolute-p filename
-This function returns @code{t} if file @var{filename} is an absolute
-file name, @code{nil} otherwise. On VMS, this function understands both
-Unix syntax and VMS syntax.
-
-@example
-@group
-(file-name-absolute-p "~rms/foo")
- @result{} t
-@end group
-@group
-(file-name-absolute-p "rms/foo")
- @result{} nil
-@end group
-@group
-(file-name-absolute-p "/user/rms/foo")
- @result{} t
-@end group
-@end example
+directory. You can use it for directory names and for file names,
+because it recognizes abbreviations even as part of the name.
@end defun
@node File Name Expansion
@defun expand-file-name filename &optional directory
This function converts @var{filename} to an absolute file name. If
-@var{directory} is supplied, it is the directory to start with if
-@var{filename} is relative. (The value of @var{directory} should itself
-be an absolute directory name; it may start with @samp{~}.)
-Otherwise, the current buffer's value of @code{default-directory} is
-used. For example:
+@var{directory} is supplied, it is the default directory to start with
+if @var{filename} is relative. (The value of @var{directory} should
+itself be an absolute directory name or directory file name; it may
+start with @samp{~}.) Otherwise, the current buffer's value of
+@code{default-directory} is used. For example:
@example
@group
@end group
@end example
+If the part of the combined file name before the first slash is
+@samp{~}, it expands to the value of the @env{HOME} environment
+variable (usually your home directory). If the part before the first
+slash is @samp{~@var{user}} and if @var{user} is a valid login name,
+it expands to @var{user}'s home directory.
+
Filenames containing @samp{.} or @samp{..} are simplified to their
canonical form:
@end group
@end example
-@samp{~/} is expanded into the user's home directory. A @samp{/} or
-@samp{~} following a @samp{/} is taken to be the start of an absolute
-file name that overrides what precedes it, so everything before that
-@samp{/} or @samp{~} is deleted. For example:
+Note that @code{expand-file-name} does @emph{not} expand environment
+variables; only @code{substitute-in-file-name} does that.
+
+Note also that @code{expand-file-name} does not follow symbolic links
+at any level. This results in a difference between the way
+@code{file-truename} and @code{expand-file-name} treat @samp{..}.
+Assuming that @samp{/tmp/bar} is a symbolic link to the directory
+@samp{/tmp/foo/bar} we get:
@example
@group
-(expand-file-name
- "/a1/gnu//usr/local/lib/emacs/etc/MACHINES")
- @result{} "/usr/local/lib/emacs/etc/MACHINES"
+(file-truename "/tmp/bar/../myfile")
+ @result{} "/tmp/foo/myfile"
@end group
@group
-(expand-file-name "/a1/gnu/~/foo")
- @result{} "/xcssun/users/rms/foo"
+(expand-file-name "/tmp/bar/../myfile")
+ @result{} "/tmp/myfile"
@end group
@end example
-@noindent
-In both cases, @file{/a1/gnu/} is discarded because an absolute file
-name follows it.
-
-Note that @code{expand-file-name} does @emph{not} expand environment
-variables; only @code{substitute-in-file-name} does that.
-@end defun
-
-@c Emacs 19 feature
-@defun file-relative-name filename directory
-This function does the inverse of expansion---it tries to return a
-relative name which is equivalent to @var{filename} when interpreted
-relative to @var{directory}. (If such a relative name would be longer
-than the absolute name, it returns the absolute name instead.)
-
-@example
-(file-relative-name "/foo/bar" "/foo/")
- @result{} "bar")
-(file-relative-name "/foo/bar" "/hack/")
- @result{} "/foo/bar")
-@end example
+If you may need to follow symbolic links preceding @samp{..}, you
+should make sure to call @code{file-truename} without prior direct or
+indirect calls to @code{expand-file-name}. @xref{Truenames}.
@end defun
@defvar default-directory
The value of this buffer-local variable is the default directory for the
current buffer. It should be an absolute directory name; it may start
-with @samp{~}. This variable is local in every buffer.
+with @samp{~}. This variable is buffer-local in every buffer.
@code{expand-file-name} uses the default directory when its second
argument is @code{nil}.
-On Unix systems, the value is always a string ending with a slash.
+Aside from VMS, the value is always a string ending with a slash.
@example
@group
@end defvar
@defun substitute-in-file-name filename
-This function replaces environment variables references in
-@var{filename} with the environment variable values. Following standard
-Unix shell syntax, @samp{$} is the prefix to substitute an environment
-variable value.
+@anchor{Definition of substitute-in-file-name}
+This function replaces environment variable references in
+@var{filename} with the environment variable values. Following
+standard Unix shell syntax, @samp{$} is the prefix to substitute an
+environment variable value. If the input contains @samp{$$}, that is
+converted to @samp{$}; this gives the user a way to ``quote'' a
+@samp{$}.
The environment variable name is the series of alphanumeric characters
(including underscores) that follow the @samp{$}. If the character following
the @samp{$} is a @samp{@{}, then the variable name is everything up to the
matching @samp{@}}.
+Calling @code{substitute-in-file-name} on output produced by
+@code{substitute-in-file-name} tends to give incorrect results. For
+instance, use of @samp{$$} to quote a single @samp{$} won't work
+properly, and @samp{$} in an environment variable's value could lead
+to repeated substitution. Therefore, programs that call this function
+and put the output where it will be passed to this function need to
+double all @samp{$} characters to prevent subsequent incorrect
+results.
+
@c Wordy to avoid overfull hbox. --rjc 15mar92
Here we assume that the environment variable @code{HOME}, which holds
the user's home directory name, has value @samp{/xcssun/users/rms}.
@end group
@end example
-If a @samp{~} or a @samp{/} appears following a @samp{/}, after
-substitution, everything before the following @samp{/} is discarded:
+After substitution, if a @samp{~} or a @samp{/} appears immediately
+after another @samp{/}, the function discards everything before it (up
+through the immediately preceding @samp{/}).
@example
@group
@group
(substitute-in-file-name "/usr/local/$HOME/foo")
@result{} "/xcssun/users/rms/foo"
+ ;; @r{@file{/usr/local/} has been discarded.}
@end group
@end example
construct a name for such a file:
@example
-(make-temp-name (concat "/tmp/" @var{name-of-application}))
+(make-temp-file @var{name-of-application})
@end example
@noindent
-Here we use the directory @file{/tmp/} because that is the standard
-place on Unix for temporary files. The job of @code{make-temp-name} is
-to prevent two different users or two different jobs from trying to use
-the same name.
-
-@defun make-temp-name string
-This function generates string that can be used as a unique name. The
-name starts with the prefix @var{string}, and ends with a number that
-is different in each Emacs job.
+The job of @code{make-temp-file} is to prevent two different users or
+two different jobs from trying to use the exact same file name.
+
+@defun make-temp-file prefix &optional dir-flag suffix
+@tindex make-temp-file
+This function creates a temporary file and returns its name. Emacs
+creates the temporary file's name by adding to @var{prefix} some
+random characters that are different in each Emacs job. The result is
+guaranteed to be a newly created empty file. On MS-DOS, this function
+can truncate the @var{string} prefix to fit into the 8+3 file-name
+limits. If @var{prefix} is a relative file name, it is expanded
+against @code{temporary-file-directory}.
@example
@group
-(make-temp-name "/tmp/foo")
- @result{} "/tmp/foo021304"
+(make-temp-file "foo")
+ @result{} "/tmp/foo232J6v"
@end group
@end example
+When @code{make-temp-file} returns, the file has been created and is
+empty. At that point, you should write the intended contents into the
+file.
+
+If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an
+empty directory instead of an empty file. It returns the file name,
+not the directory name, of that directory. @xref{Directory Names}.
+
+If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at
+the end of the file name.
+
To prevent conflicts among different libraries running in the same
-Emacs, each Lisp program that uses @code{make-temp-name} should have its
-own @var{string}. The number added to the end of the name distinguishes
-between the same application running in different Emacs jobs.
+Emacs, each Lisp program that uses @code{make-temp-file} should have its
+own @var{prefix}. The number added to the end of @var{prefix}
+distinguishes between the same application running in different Emacs
+jobs. Additional added characters permit a large number of distinct
+names even in one Emacs job.
+@end defun
+
+ The default directory for temporary files is controlled by the
+variable @code{temporary-file-directory}. This variable gives the user
+a uniform way to specify the directory for all temporary files. Some
+programs use @code{small-temporary-file-directory} instead, if that is
+non-@code{nil}. To use it, you should expand the prefix against
+the proper directory before calling @code{make-temp-file}.
+
+ In older Emacs versions where @code{make-temp-file} does not exist,
+you should use @code{make-temp-name} instead:
+
+@example
+(make-temp-name
+ (expand-file-name @var{name-of-application}
+ temporary-file-directory))
+@end example
+
+@defun make-temp-name string
+This function generates a string that can be used as a unique file
+name. The name starts with @var{string}, and has several random
+characters appended to it, which are different in each Emacs job. It
+is like @code{make-temp-file} except that it just constructs a name,
+and does not create a file. Another difference is that @var{string}
+should be an absolute file name. On MS-DOS, this function can
+truncate the @var{string} prefix to fit into the 8+3 file-name limits.
@end defun
+@defvar temporary-file-directory
+@cindex @code{TMPDIR} environment variable
+@cindex @code{TMP} environment variable
+@cindex @code{TEMP} environment variable
+This variable specifies the directory name for creating temporary files.
+Its value should be a directory name (@pxref{Directory Names}), but it
+is good for Lisp programs to cope if the value is a directory's file
+name instead. Using the value as the second argument to
+@code{expand-file-name} is a good way to achieve that.
+
+The default value is determined in a reasonable way for your operating
+system; it is based on the @code{TMPDIR}, @code{TMP} and @code{TEMP}
+environment variables, with a fall-back to a system-dependent name if
+none of these variables is defined.
+
+Even if you do not use @code{make-temp-file} to create the temporary
+file, you should still use this variable to decide which directory to
+put the file in. However, if you expect the file to be small, you
+should use @code{small-temporary-file-directory} first if that is
+non-@code{nil}.
+@end defvar
+
+@tindex small-temporary-file-directory
+@defvar small-temporary-file-directory
+This variable specifies the directory name for
+creating certain temporary files, which are likely to be small.
+
+If you want to write a temporary file which is likely to be small, you
+should compute the directory like this:
+
+@example
+(make-temp-file
+ (expand-file-name @var{prefix}
+ (or small-temporary-file-directory
+ temporary-file-directory)))
+@end example
+@end defvar
+
@node File Name Completion
@subsection File Name Completion
@cindex file name completion subroutines
information.
The argument @var{partial-filename} must be a file name containing no
-directory part and no slash. The current buffer's default directory is
-prepended to @var{directory}, if @var{directory} is not absolute.
+directory part and no slash (or backslash on some systems). The current
+buffer's default directory is prepended to @var{directory}, if
+@var{directory} is not absolute.
-In the following example, suppose that the current default directory,
-@file{~rms/lewis}, has five files whose names begin with @samp{f}:
+In the following example, suppose that @file{~rms/lewis} is the current
+default directory, and has five files whose names begin with @samp{f}:
@file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and
@file{file.c.~2~}.@refill
@example
@group
(file-name-all-completions "f" "")
- @result{} ("foo" "file~" "file.c.~2~"
+ @result{} ("foo" "file~" "file.c.~2~"
"file.c.~1~" "file.c")
@end group
@group
-(file-name-all-completions "fo" "")
+(file-name-all-completions "fo" "")
@result{} ("foo")
@end group
@end example
@defopt completion-ignored-extensions
@code{file-name-completion} usually ignores file names that end in any
string in this list. It does not ignore them when all the possible
-completions end in one of these suffixes or when a buffer showing all
-possible completions is displayed.@refill
+completions end in one of these suffixes. This variable has no effect
+on @code{file-name-all-completions}.@refill
A typical value might look like this:
@result{} (".o" ".elc" "~" ".dvi")
@end group
@end example
+
+If an element of @code{completion-ignored-extensions} ends in a slash
+@samp{/}, it signals a directory. The elements which do @emph{not} end
+in a slash will never match a directory; thus, the above value will not
+filter out a directory named @file{foo.elc}.
@end defopt
+@node Standard File Names
+@subsection Standard File Names
+
+ Most of the file names used in Lisp programs are entered by the user.
+But occasionally a Lisp program needs to specify a standard file name
+for a particular use---typically, to hold customization information
+about each user. For example, abbrev definitions are stored (by
+default) in the file @file{~/.abbrev_defs}; the @code{completion}
+package stores completions in the file @file{~/.completions}. These are
+two of the many standard file names used by parts of Emacs for certain
+purposes.
+
+ Various operating systems have their own conventions for valid file
+names and for which file names to use for user profile data. A Lisp
+program which reads a file using a standard file name ought to use, on
+each type of system, a file name suitable for that system. The function
+@code{convert-standard-filename} makes this easy to do.
+
+@defun convert-standard-filename filename
+This function alters the file name @var{filename} to fit the conventions
+of the operating system in use, and returns the result as a new string.
+@end defun
+
+ The recommended way to specify a standard file name in a Lisp program
+is to choose a name which fits the conventions of GNU and Unix systems,
+usually with a nondirectory part that starts with a period, and pass it
+to @code{convert-standard-filename} instead of using it directly. Here
+is an example from the @code{completion} package:
+
+@example
+(defvar save-completions-file-name
+ (convert-standard-filename "~/.completions")
+ "*The file name to save completions to.")
+@end example
+
+ On GNU and Unix systems, and on some other systems as well,
+@code{convert-standard-filename} returns its argument unchanged. On
+some other systems, it alters the name to fit the system's conventions.
+
+ For example, on MS-DOS the alterations made by this function include
+converting a leading @samp{.} to @samp{_}, converting a @samp{_} in the
+middle of the name to @samp{.} if there is no other @samp{.}, inserting
+a @samp{.} after eight characters if there is none, and truncating to
+three characters after the @samp{.}. (It makes other changes as well.)
+Thus, @file{.abbrev_defs} becomes @file{_abbrev.def}, and
+@file{.completions} becomes @file{_complet.ion}.
+
@node Contents of Directories
@section Contents of Directories
@cindex directory-oriented functions
@group
(directory-files "~lewis")
@result{} ("#foo#" "#foo.el#" "." ".."
- "dired-mods.el" "files.texi"
+ "dired-mods.el" "files.texi"
"files.texi.~1~")
@end group
@end example
that can be read.
@end defun
+@defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format
+This is similar to @code{directory-files} in deciding which files
+to report on and how to report their names. However, instead
+of returning a list of file names, it returns for each file a
+list @code{(@var{filename} . @var{attributes})}, where @var{attributes}
+is what @code{file-attributes} would return for that file.
+The optional argument @var{id-format} has the same meaning as the
+corresponding argument to @code{file-attributes} (@pxref{Definition
+of file-attributes}).
+@end defun
+
@defun file-name-all-versions file dirname
This function returns a list of all versions of the file named
-@var{file} in directory @var{dirname}.
+@var{file} in directory @var{dirname}. It is only available on VMS.
+@end defun
+
+@tindex file-expand-wildcards
+@defun file-expand-wildcards pattern &optional full
+This function expands the wildcard pattern @var{pattern}, returning
+a list of file names that match it.
+
+If @var{pattern} is written as an absolute file name,
+the values are absolute also.
+
+If @var{pattern} is written as a relative file name, it is interpreted
+relative to the current default directory. The file names returned are
+normally also relative to the current default directory. However, if
+@var{full} is non-@code{nil}, they are absolute.
@end defun
@defun insert-directory file switches &optional wildcard full-directory-p
-This function inserts a directory listing for directory @var{dir},
-formatted with @code{ls} according to @var{switches}. It leaves point
-after the inserted text.
+This function inserts (in the current buffer) a directory listing for
+directory @var{file}, formatted with @code{ls} according to
+@var{switches}. It leaves point after the inserted text.
+@var{switches} may be a string of options, or a list of strings
+representing individual options.
-The argument @var{dir} may be either a directory name or a file
+The argument @var{file} may be either a directory name or a file
specification including wildcard characters. If @var{wildcard} is
non-@code{nil}, that means treat @var{file} as a file specification with
wildcards.
-If @var{full-directory-p} is non-@code{nil}, that means @var{file} is a
-directory and switches do not contain @samp{d}, so that a full listing
-is expected.
+If @var{full-directory-p} is non-@code{nil}, that means the directory
+listing is expected to show the full contents of a directory. You
+should specify @code{t} when @var{file} is a directory and switches do
+not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to
+describe a directory itself as a file, rather than showing its
+contents.)
-This function works by running a directory listing program whose name is
-in the variable @code{insert-directory-program}. If @var{wildcard} is
-non-@code{nil}, it also runs the shell specified by
+On most systems, this function works by running a directory listing
+program whose name is in the variable @code{insert-directory-program}.
+If @var{wildcard} is non-@code{nil}, it also runs the shell specified by
@code{shell-file-name}, to expand the wildcards.
+
+MS-DOS and MS-Windows systems usually lack the standard Unix program
+@code{ls}, so this function emulates the standard Unix program @code{ls}
+with Lisp code.
+
+As a technical detail, when @var{switches} contains the long
+@samp{--dired} option, @code{insert-directory} treats it specially,
+for the sake of dired. However, the normally equivalent short
+@samp{-D} option is just passed on to @code{insert-directory-program},
+as any other option.
@end defun
@defvar insert-directory-program
This variable's value is the program to run to generate a directory listing
-for the function @code{insert-directory}.
+for the function @code{insert-directory}. It is ignored on systems
+which generate the listing with Lisp code.
@end defvar
@node Create/Delete Dirs
@section Creating and Deleting Directories
@c Emacs 19 features
-@defun make-directory dirname
+ Most Emacs Lisp file-manipulation functions get errors when used on
+files that are directories. For example, you cannot delete a directory
+with @code{delete-file}. These special functions exist to create and
+delete directories.
+
+@defun make-directory dirname &optional parents
This function creates a directory named @var{dirname}.
+If @var{parents} is non-@code{nil}, as is always the case in an
+interactive call, that means to create the parent directories first,
+if they don't already exist.
@end defun
@defun delete-directory dirname
This function deletes the directory named @var{dirname}. The function
@code{delete-file} does not work for files that are directories; you
-must use @code{delete-directory} in that case.
+must use @code{delete-directory} for them. If the directory contains
+any files, @code{delete-directory} signals an error.
+
+This function only follows symbolic links at the level of parent
+directories.
@end defun
@node Magic File Names
@cindex magic file names
@c Emacs 19 feature
-You can implement special handling for certain file names. This is
-called making those names @dfn{magic}. You must supply a regular
-expression to define the class of names (all those which match the
+ You can implement special handling for certain file names. This is
+called making those names @dfn{magic}. The principal use for this
+feature is in implementing remote file names (@pxref{Remote Files,,
+Remote Files, emacs, The GNU Emacs Manual}).
+
+ To define a kind of magic file name, you must supply a regular
+expression to define the class of names (all those that match the
regular expression), plus a handler that implements all the primitive
Emacs file operations for file names that do match.
-The value of @code{file-name-handler-alist} is a list of handlers,
+ The variable @code{file-name-handler-alist} holds a list of handlers,
together with regular expressions that determine when to apply each
handler. Each element has this form:
the file name matches @var{regexp}, the primitives handle that file by
calling @var{handler}.
-The first argument given to @var{handler} is the name of the primitive;
-the remaining arguments are the arguments that were passed to that
-operation. (The first of these arguments is typically the file name
-itself.) For example, if you do this:
+ The first argument given to @var{handler} is the name of the
+primitive, as a symbol; the remaining arguments are the arguments that
+were passed to that primitive. (The first of these arguments is most
+often the file name itself.) For example, if you do this:
@example
(file-exists-p @var{filename})
(funcall @var{handler} 'file-exists-p @var{filename})
@end example
-Here are the operations that you can handle for a magic file name:
+ When a function takes two or more arguments that must be file names,
+it checks each of those names for a handler. For example, if you do
+this:
+
+@example
+(expand-file-name @var{filename} @var{dirname})
+@end example
+
+@noindent
+then it checks for a handler for @var{filename} and then for a handler
+for @var{dirname}. In either case, the @var{handler} is called like
+this:
+
+@example
+(funcall @var{handler} 'expand-file-name @var{filename} @var{dirname})
+@end example
+
+@noindent
+The @var{handler} then needs to figure out whether to handle
+@var{filename} or @var{dirname}.
+
+ If the specified file name matches more than one handler, the one
+whose match starts last in the file name gets precedence. This rule
+is chosen so that handlers for jobs such as uncompression are handled
+first, before handlers for jobs such as remote file access.
+Here are the operations that a magic file name handler gets to handle:
+
+@ifnottex
@noindent
-@code{add-name-to-file}, @code{copy-file}, @code{delete-directory},
-@code{delete-file},@*
+@code{access-file}, @code{add-name-to-file},
+@code{byte-compiler-base-file-name},@*
+@code{copy-file}, @code{delete-directory},
+@code{delete-file},
+@code{diff-latest-backup-file},
@code{directory-file-name},
-@code{diff-latest-backup-file}, @code{directory-files},
-@code{dired-compress-file}, @code{dired-uncache},
-@code{expand-file-name},@*
+@code{directory-files},
+@code{directory-files-and-attributes},
+@code{dired-call-process},
+@code{dired-compress-file}, @code{dired-uncache},@*
+@code{expand-file-name},
@code{file-accessible-directory-p},
-@code{file-attributes}, @code{file-directory-p},
-@code{file-executable-p}, @code{file-exists-p}, @code{file-local-copy},
+@code{file-attributes},
+@code{file-directory-p},
+@code{file-executable-p}, @code{file-exists-p},
+@code{file-local-copy}, @code{file-remote-p},
@code{file-modes}, @code{file-name-all-completions},
-@code{file-name-as-directory}, @code{file-name-completion},
-@code{file-name-directory}, @code{file-name-nondirectory},
+@code{file-name-as-directory},
+@code{file-name-completion},
+@code{file-name-directory},
+@code{file-name-nondirectory},
@code{file-name-sans-versions}, @code{file-newer-than-file-p},
-@code{file-readable-p}, @code{file-symlink-p}, @code{file-truename},
-@code{file-writable-p},@*
+@code{file-ownership-preserved-p},
+@code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
+@code{file-truename}, @code{file-writable-p},
+@code{find-backup-file-name},
+@code{find-file-noselect},@*
+@code{get-file-buffer},
@code{insert-directory},
-@code{insert-file-contents}, @code{load}, @code{make-directory},
-@code{make-symbolic-link}, @code{rename-file}, @code{set-file-modes},
-@code{set-visited-file-modtime}, @code{unhandled-file-name-directory},
-@code{verify-visited-file-modtime}, @code{write-region}.
-
-The handler function must handle all of the above operations, and
-possibly others to be added in the future. Therefore, it should always
-reinvoke the ordinary Lisp primitive when it receives an operation it
-does not recognize. Here's one way to do this:
+@code{insert-file-contents},@*
+@code{load},
+@code{make-auto-save-file-name},
+@code{make-directory},
+@code{make-directory-internal},
+@code{make-symbolic-link},@*
+@code{rename-file}, @code{set-file-modes}, @code{set-file-times},
+@code{set-visited-file-modtime}, @code{shell-command},
+@code{substitute-in-file-name},@*
+@code{unhandled-file-name-directory},
+@code{vc-registered},
+@code{verify-visited-file-modtime},@*
+@code{write-region}.
+@end ifnottex
+@iftex
+@noindent
+@flushleft
+@code{access-file}, @code{add-name-to-file},
+@code{byte-com@discretionary{}{}{}piler-base-file-name},
+@code{copy-file}, @code{delete-directory},
+@code{delete-file},
+@code{diff-latest-backup-file},
+@code{directory-file-name},
+@code{directory-files},
+@code{directory-files-and-at@discretionary{}{}{}tributes},
+@code{dired-call-process},
+@code{dired-compress-file}, @code{dired-uncache},
+@code{expand-file-name},
+@code{file-accessible-direc@discretionary{}{}{}tory-p},
+@code{file-attributes},
+@code{file-direct@discretionary{}{}{}ory-p},
+@code{file-executable-p}, @code{file-exists-p},
+@code{file-local-copy}, @code{file-remote-p},
+@code{file-modes}, @code{file-name-all-completions},
+@code{file-name-as-directory},
+@code{file-name-completion},
+@code{file-name-directory},
+@code{file-name-nondirec@discretionary{}{}{}tory},
+@code{file-name-sans-versions}, @code{file-newer-than-file-p},
+@code{file-ownership-pre@discretionary{}{}{}served-p},
+@code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
+@code{file-truename}, @code{file-writable-p},
+@code{find-backup-file-name},
+@code{find-file-noselect},
+@code{get-file-buffer},
+@code{insert-directory},
+@code{insert-file-contents},
+@code{load}, @code{make-direc@discretionary{}{}{}tory},
+@code{make-direc@discretionary{}{}{}tory-internal},
+@code{make-symbolic-link},
+@code{rename-file}, @code{set-file-modes},
+@code{set-visited-file-modtime}, @code{shell-command},
+@code{substitute-in-file-name},
+@code{unhandled-file-name-directory},
+@code{vc-regis@discretionary{}{}{}tered},
+@code{verify-visited-file-modtime},
+@code{write-region}.
+@end flushleft
+@end iftex
+
+ Handlers for @code{insert-file-contents} typically need to clear the
+buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the
+@var{visit} argument is non-@code{nil}. This also has the effect of
+unlocking the buffer if it is locked.
+
+ The handler function must handle all of the above operations, and
+possibly others to be added in the future. It need not implement all
+these operations itself---when it has nothing special to do for a
+certain operation, it can reinvoke the primitive, to handle the
+operation ``in the usual way''. It should always reinvoke the primitive
+for an operation it does not recognize. Here's one way to do this:
@smallexample
(defun my-file-handler (operation &rest args)
@dots{}
;; @r{Handle any operation we don't know about.}
(t (let ((inhibit-file-name-handlers
- (cons 'ange-ftp-file-handler
- (and (eq inhibit-file-name-operation operation)
- inhibit-file-name-handlers)))
- (inhibit-file-name-operation operation))
+ (cons 'my-file-handler
+ (and (eq inhibit-file-name-operation operation)
+ inhibit-file-name-handlers)))
+ (inhibit-file-name-operation operation))
(apply operation args)))))
@end smallexample
-When a handler function decides to call the ordinary Emacs primitive for
+ When a handler function decides to call the ordinary Emacs primitive for
the operation at hand, it needs to prevent the primitive from calling
the same handler once again, thus leading to an infinite recursion. The
example above shows how to do this, with the variables
multiple handlers, and for operations that have two file names that may
each have handlers.
+@kindex safe-magic (@r{property})
+ Handlers that don't really do anything special for actual access to the
+file---such as the ones that implement completion of host names for
+remote file names---should have a non-@code{nil} @code{safe-magic}
+property. For instance, Emacs normally ``protects'' directory names
+it finds in @code{PATH} from becoming magic, if they look like magic
+file names, by prefixing them with @samp{/:}. But if the handler that
+would be used for them has a non-@code{nil} @code{safe-magic}
+property, the @samp{/:} is not added.
+
+@kindex operations (@r{property})
+ A file name handler can have an @code{operations} property to
+declare which operations it handles in a nontrivial way. If this
+property has a non-@code{nil} value, it should be a list of
+operations; then only those operations will call the handler. This
+avoids inefficiency, but its main purpose is for autoloaded handler
+functions, so that they won't be loaded except when they have real
+work to do.
+
@defvar inhibit-file-name-handlers
This variable holds a list of handlers whose use is presently inhibited
for a certain operation.
@end defvar
@defun find-file-name-handler file operation
-This function returns the handler function for file name @var{file}, or
-@code{nil} if there is none. The argument @var{operation} should be the
-operation to be performed on the file---the value you will pass to the
-handler as its first argument when you call it. The operation is needed
-for comparison with @code{inhibit-file-name-operation}.
+This function returns the handler function for file name @var{file},
+or @code{nil} if there is none. The argument @var{operation} should
+be the operation to be performed on the file---the value you will pass
+to the handler as its first argument when you call it. If
+@var{operation} equals @code{inhibit-file-name-operation}, or if it is
+not found in the @code{operations} property of the handler, this
+function returns @code{nil}.
@end defun
@defun file-local-copy filename
-This function copies file @var{filename} to the local site, if it isn't
-there already. If @var{filename} specifies a ``magic'' file name which
-programs outside Emacs cannot directly read or write, this copies the
-contents to an ordinary file and returns that file's name.
+This function copies file @var{filename} to an ordinary non-magic file
+on the local machine, if it isn't on the local machine already. Magic
+file names should handle the @code{file-local-copy} operation if they
+refer to files on other machines. A magic file name that is used for
+other purposes than remote file access should not handle
+@code{file-local-copy}; then this function will treat the file as
+local.
+
+If @var{filename} is local, whether magic or not, this function does
+nothing and returns @code{nil}. Otherwise it returns the file name
+of the local copy file.
+@end defun
-If @var{filename} is an ordinary file name, not magic, then this function
-does nothing and returns @code{nil}.
+@defun file-remote-p filename
+This function tests whether @var{filename} is a remote file. If
+@var{filename} is local (not remote), the return value is @code{nil}.
+If @var{filename} is indeed remote, the return value is a string that
+identifies the remote system.
+
+This identifier string can include a host name and a user name, as
+well as characters designating the method used to access the remote
+system. For example, the remote identifier string for the filename
+@code{/ssh:user@@host:/some/file} is @code{/ssh:user@@host:}.
+
+If @code{file-remote-p} returns the same identifier for two different
+filenames, that means they are stored on the same file system and can
+be accessed locally with respect to each other. This means, for
+example, that it is possible to start a remote process accessing both
+files at the same time. Implementors of file handlers need to ensure
+this principle is valid.
@end defun
@defun unhandled-file-name-directory filename
-This function returns the name of a directory that is not magic.
-It uses the directory part of @var{filename} if that is not magic.
-Otherwise, it asks the handler what to do.
+This function returns the name of a directory that is not magic. It
+uses the directory part of @var{filename} if that is not magic. For a
+magic file name, it invokes the file name handler, which therefore
+decides what value to return.
This is useful for running a subprocess; every subprocess must have a
non-magic directory to serve as its current directory, and this function
is a good way to come up with one.
@end defun
-@node Files and MS-DOS
-@section Files and MS-DOS
-@cindex MS-DOS file types
-@cindex file types on MS-DOS
-@cindex text files and binary files
-@cindex binary files and text files
-
- Emacs on MS-DOS makes a distinction between text files and binary
-files. This is necessary because ordinary text files on MS-DOS use two
-characters between lines: carriage-return and linefeed. Emacs expects
-just a newline character (a linefeed) between lines. When Emacs reads
-or writes a text file on MS-DOS, it needs to convert the line
-separators. This means it needs to know which files are text files and
-which are binary. It makes this decision when visiting a file, and
-records the decision in the variable @code{buffer-file-type} for when
-the file is saved.
-
-@defvar buffer-file-type
-This variable, automatically local in each buffer, records the file type
-of the buffer's visited file.
+@node Format Conversion
+@section File Format Conversion
+
+@cindex file format conversion
+@cindex encoding file formats
+@cindex decoding file formats
+ The variable @code{format-alist} defines a list of @dfn{file formats},
+which describe textual representations used in files for the data (text,
+text-properties, and possibly other information) in an Emacs buffer.
+Emacs performs format conversion if appropriate when reading and writing
+files.
+
+@defvar format-alist
+This list contains one format definition for each defined file format.
@end defvar
-@defun find-buffer-file-type filename
-This function determines whether file @var{filename} is a text file
-or a binary file. It returns @code{nil} for text, @code{t} for binary.
-@end defun
+@cindex format definition
+Each format definition is a list of this form:
-@defopt file-name-buffer-file-type-alist
-This variable holds an alist for distinguishing text files from binary
-files. Each element has the form (@var{regexp} . @var{type}), where
-@var{regexp} is matched against the file name, and @var{type} may be is
-@code{nil} for text, @code{t} for binary, or a function to call to
-compute which. If it is a function, then it is called with a single
-argument (the file name) and should return @code{t} or @code{nil}.
-@end defopt
+@example
+(@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn})
+@end example
-@defopt default-buffer-file-type
-This variable specifies the default file type for files whose names
-don't indicate anything in particular. Its value should be @code{nil}
-for text, or @code{t} for binary.
-@end defopt
+Here is what the elements in a format definition mean:
+
+@table @var
+@item name
+The name of this format.
+
+@item doc-string
+A documentation string for the format.
+
+@item regexp
+A regular expression which is used to recognize files represented in
+this format.
+
+@item from-fn
+A shell command or function to decode data in this format (to convert
+file data into the usual Emacs data representation).
+
+A shell command is represented as a string; Emacs runs the command as a
+filter to perform the conversion.
+
+If @var{from-fn} is a function, it is called with two arguments, @var{begin}
+and @var{end}, which specify the part of the buffer it should convert.
+It should convert the text by editing it in place. Since this can
+change the length of the text, @var{from-fn} should return the modified
+end position.
+
+One responsibility of @var{from-fn} is to make sure that the beginning
+of the file no longer matches @var{regexp}. Otherwise it is likely to
+get called again.
+
+@item to-fn
+A shell command or function to encode data in this format---that is, to
+convert the usual Emacs data representation into this format.
+
+If @var{to-fn} is a string, it is a shell command; Emacs runs the
+command as a filter to perform the conversion.
-@deffn Command find-file-text filename
-Like @code{find-file}, but treat the file as text regardless of its name.
+If @var{to-fn} is a function, it is called with two arguments, @var{begin}
+and @var{end}, which specify the part of the buffer it should convert.
+There are two ways it can do the conversion:
+
+@itemize @bullet
+@item
+By editing the buffer in place. In this case, @var{to-fn} should
+return the end-position of the range of text, as modified.
+
+@item
+By returning a list of annotations. This is a list of elements of the
+form @code{(@var{position} . @var{string})}, where @var{position} is an
+integer specifying the relative position in the text to be written, and
+@var{string} is the annotation to add there. The list must be sorted in
+order of position when @var{to-fn} returns it.
+
+When @code{write-region} actually writes the text from the buffer to the
+file, it intermixes the specified annotations at the corresponding
+positions. All this takes place without modifying the buffer.
+@end itemize
+
+@item modify
+A flag, @code{t} if the encoding function modifies the buffer, and
+@code{nil} if it works by returning a list of annotations.
+
+@item mode-fn
+A minor-mode function to call after visiting a file converted from this
+format. The function is called with one argument, the integer 1;
+that tells a minor-mode function to enable the mode.
+@end table
+
+The function @code{insert-file-contents} automatically recognizes file
+formats when it reads the specified file. It checks the text of the
+beginning of the file against the regular expressions of the format
+definitions, and if it finds a match, it calls the decoding function for
+that format. Then it checks all the known formats over again.
+It keeps checking them until none of them is applicable.
+
+Visiting a file, with @code{find-file-noselect} or the commands that use
+it, performs conversion likewise (because it calls
+@code{insert-file-contents}); it also calls the mode function for each
+format that it decodes. It stores a list of the format names in the
+buffer-local variable @code{buffer-file-format}.
+
+@defvar buffer-file-format
+This variable states the format of the visited file. More precisely,
+this is a list of the file format names that were decoded in the course
+of visiting the current buffer's file. It is always buffer-local in all
+buffers.
+@end defvar
+
+When @code{write-region} writes data into a file, it first calls the
+encoding functions for the formats listed in @code{buffer-file-format},
+in the order of appearance in the list.
+
+@deffn Command format-write-file file format &optional confirm
+This command writes the current buffer contents into the file
+@var{file} in format @var{format}, and makes that format the default
+for future saves of the buffer. The argument @var{format} is a list
+of format names. Except for the @var{format} argument, this command
+is similar to @code{write-file}. In particular, @var{confirm} has the
+same meaning and interactive treatment as the corresponding argument
+to @code{write-file}. @xref{Definition of write-file}.
+@end deffn
+
+@deffn Command format-find-file file format
+This command finds the file @var{file}, converting it according to
+format @var{format}. It also makes @var{format} the default if the
+buffer is saved later.
+
+The argument @var{format} is a list of format names. If @var{format} is
+@code{nil}, no conversion takes place. Interactively, typing just
+@key{RET} for @var{format} specifies @code{nil}.
@end deffn
-@deffn Command find-file-binary filename
-Like @code{find-file}, but treat the file as binary regardless of its
-name.
+@deffn Command format-insert-file file format &optional beg end
+This command inserts the contents of file @var{file}, converting it
+according to format @var{format}. If @var{beg} and @var{end} are
+non-@code{nil}, they specify which part of the file to read, as in
+@code{insert-file-contents} (@pxref{Reading from Files}).
+
+The return value is like what @code{insert-file-contents} returns: a
+list of the absolute file name and the length of the data inserted
+(after conversion).
+
+The argument @var{format} is a list of format names. If @var{format} is
+@code{nil}, no conversion takes place. Interactively, typing just
+@key{RET} for @var{format} specifies @code{nil}.
@end deffn
+
+@defvar buffer-auto-save-file-format
+This variable specifies the format to use for auto-saving. Its value is
+a list of format names, just like the value of
+@code{buffer-file-format}; however, it is used instead of
+@code{buffer-file-format} for writing auto-save files. If the value
+is @code{t}, the default, auto-saving uses the same format as a
+regular save in the same buffer. This variable is always buffer-local
+in all buffers.
+@end defvar
+
+@ignore
+ arch-tag: 141f74ce-6ae3-40dc-a6c4-ef83fc4ec35c
+@end ignore