⟦b362d0b27⟧

TextFile

@setfilename ../info/files
@node Files, Backups and Auto Saving, Documentation, Top
@comment  node-name,  next,  previous,  up
@chapter Files

  In Emacs, you can find, create, view, save, and otherwise work with
files and directories.  Not all of the file-related functions are
described in this chapter; some are described in @ref{Buffers}; and,
functions related to backups and auto saving are described in
@ref{Backups and Auto Saving}.

@menu
* Visiting Files::      
* Saving Buffers::      
* Reading from Files::  
* Writing to Files::    
* File Locks::  
* Information about Files::     
* Contents of Directories::     
* Changing File Names and Attributes::  
* File Names::  
@end menu

@node Visiting Files, Saving Buffers, Files, Files
@section Visiting Files
@cindex finding files
@cindex visiting files

  Visiting a file means reading a file into a buffer.  Once this is
done, we say that the buffer is @dfn{visiting} that file, and call the
file ``the visited file'' of the buffer.

  A file and a buffer are two different entities.  A file is information
recorded permanently in the computer (unless you delete it).  A buffer,
on the other hand, is information inside of Emacs that will vanish at
the end of the editing session (or when you kill the buffer).  Usually,
a buffer contains information that you have copied from a file; thus, we
say the buffer is visiting that file.  This copy is what you work
on and modify.  Changes to the buffer do not change the file, until you
save the file.  When you save the file, the buffer is copied to the file
and is thus saved permanently.

  In spite of the distinction between files and buffers, people often
refer to a file when they mean a buffer and vice-versa.  Indeed, most
people say, ``I am editing a file,'' rather than saying, ``I am
editing a buffer which I will soon save as a file of the same name.''
It is almost always clear from context what people mean.  When dealing
with a computer program, however, it is well to keep the distinction
in mind, since the computer is not as smart as a person.

  For historical reasons, these functions are called @code{find-@dots{}},
rather than @code{visit-@dots{}}.

  @xref{Buffer File Name}, for functions and variables that relate to
the visited file name of a buffer.

@deffn Command find-file  filename
  This function reads @var{filename} into a buffer and displays that
buffer in the selected window, in which the user may edit it.

The body of the @code{find-file} function is very simple and looks
like this:

@example
(switch-to-buffer (find-file-noselect filename))
@end example

@noindent
(See @code{switch-to-buffer} in @ref{Changing Buffers}.)

  When @code{find-file} is called interactively, Emacs prompts for
@var{filename} in the minibuffer.
@end deffn

@defun find-file-noselect filename
  This function is the guts of all the file-visting functions.  It reads
a file into a buffer and returns the buffer.  You may then display the
buffer in a window if you wish, but this function does not do so.  The
buffer is not made the current buffer.  (If you wish to edit the file,
you have to switch to it.)

  If no buffer is currently visiting @var{filename}, then one is created
and the file is visited.  If @var{filename} does not exist, it is
created as empty, and Emacs displays a message @samp{New file} in the
echo area.

  If a buffer is already visiting @var{filename}, then
@code{find-file-noselect} verifies that the file has not changed since
it was last visited or saved, and returns that buffer.  If the file has
changed, then this function offers to re-read the changed file.  If the
user says @samp{yes}, any changes previously made in the buffer will be
lost.

  The @code{find-file-noselect} function calls @code{after-find-file}
after the file is found.  The @code{after-find-file} 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 hooks in @code{find-file-hooks}.

  The @code{find-file-noselect} function returns the buffer visiting the
file.  

@example
(find-file-noselect "foo")
     @result{} #<buffer foo>
@end example

  Note that the @code{find-file-noselect} function checks whether a
buffer is already visiting @var{filename}; if it is, the function
verifies that the file has not changed since it was last visited or
saved, and returns that buffer.  If the file has changed, Emacs offers
to read in the changed file.  If the user says @samp{yes}, any changes
made to the buffer will be lost.
@end defun

@deffn Command find-alternate-file filename
  This function reads in the file @var{filename}, and selects its
buffer, killing the previous buffer.  If your current buffer contains an
empty file that you just visited by mistake, use this command to visit
the file you really want.

  When this function is called interactively, Emacs prompts you for
@var{filename}.
@end deffn

@deffn Command find-file-other-window filename
  This function visits the file @var{filename}, and displays its buffer
in a window other than the selected window.  If there are two or more
windows on the screen, then the non-selected window will be used.  If
there is only one window, it will be split.  The function returns
@code{nil}.

  When this function is called interactively, Emacs prompts for
@var{filename}.
@end deffn

@deffn Command find-file-read-only filename
  This function visits the file named @var{filename} and selects its
buffer, just like @code{find-file}, but it marks the buffer as
read-only.  @xref{Read Only Buffers}, for related functions and
variables.

  When this function is called interactively, Emacs prompts for
@var{filename}.
@end deffn

@deffn Command view-file filename
  This function views @var{filename} in @dfn{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.

  After loading the file, @code{view-file} calls the value of
@code{view-hook} if that is non-@code{nil}.

  When this function is called interactively, Emacs prompts for
@var{filename} in the minibuffer.
@end deffn

@defvar find-file-hooks
  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 hooks are fun.
@end defvar

@defvar find-file-not-found-hooks
  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
@var{filename}.  These functions are called as soon as the error is
detected.  @code{buffer-file-name} is already set up.  The functions are
called in the order given, until one of them returns non-@code{nil}.
@end defvar

@menu
* Subroutines of Visiting::      
@end menu

@node Subroutines of Visiting,  , Visiting Files, Visiting Files
@comment  node-name,  next,  previous,  up
@subsection Subroutines of Visiting

  The @code{find-file-noselect} function uses the @code{after-find-file}
and @code{create-file-buffer} functions.

@defun after-find-file &optional error warn
  This function is called by @code{find-file-noselect} and by the
default revert function (@pxref{Reverting}).  It sets the buffer major
mode, and parses local variables.

@cindex New File message
@cindex file open error
   If there was an error in opening the file, the calling function
should pass @var{error} a non-@code{nil} value.  In that case,
@code{after-find-file} issues a warning: @samp{(New File)}.  Note that,
for serious errors, you would not even call @code{after-find-file}.
Only ``file not found'' errors get here with a non-@code{nil}
@var{error}.

  If @var{warn} is non-@code{nil}, then Emacs will issue a warning if there
exists an auto-save file more recent than the visited file.

  The last thing @code{after-find-file} does is call all the functions
in @code{find-file-hooks}.
@end defun

@defun create-file-buffer filename
  This function creates a suitably named buffer for visiting @var{filename},
and returns it.  The string @var{filename} (sans directory) is used
unchanged if that name is free; otherwise a string such as @samp{<2>} is
appended to get an unused name.  Also @pxref{Creating Buffers}.

  Note: @code{create-file-buffer} does @emph{not} associate the new buffer
with any file and does not make it the current buffer.

@example
(create-file-buffer "foo")
     @result{} #<buffer foo>
(create-file-buffer "foo")
     @result{} #<buffer foo<2>>
(create-file-buffer "foo")
     @result{} #<buffer foo<3>>
@end example

  This function is used by @code{find-file-noselect}.
@end defun

@node Saving Buffers, Reading from Files, Visiting Files, Files
@section Saving Buffers

  When you work on a file in Emacs, you are actually working on a buffer
that is visiting that file---that is, the contents of the file are
copied into the buffer and the copy is what you work on and modify.
Changes to the buffer do not change the file, until you save the buffer
as a newly written file.  The save buffer commands do this.

@deffn Command save-buffer &optional backup-option
  This function saves the contents of the current buffer in its
visited file if the buffer has been modified.  Otherwise, it does nothing.

  If @var{backup-option} is @code{nil}, the @code{save-buffer} function
make a backup file only if this is the first save or if the buffer was
previously modified.

  The @code{save-buffer} function is designed for interactive use; and
the value of @var{backup-option} then depends of the number of @kbd{C-u}
keystrokes prefixing the @code{save-buffer} command.

@itemize @bullet
@item
With 1 or 3 @kbd{C-u}'s, the @code{save-buffer} function marks this
version of the buffer to be backed up.  

@item
With 2 or 3 @kbd{C-u}'s, the @code{save-buffer} function
unconditionally backs up previous version.   
@end itemize

  If a file's name is @file{foo}, the names of its numbered backup
versions are @file{foo.~@var{v}~}, for various integers @var{v}, like
this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{},
@file{foo.~259~}, and so on.  A non-numbered backup file is called
@file{foo~}.

  Numeric backups (rather than @file{foo~}) will be made if the value
of @code{version-control} is not the symbol @code{never}, and either
there are already numeric versions of the file being backed up or else
@code{version-control} is non-@code{nil}.  (Thus, numeric backups will
be kept if the value of @code{version-control} is @code{t}.)

  @code{dired-kept-versions} controls @code{dired}'s
@code{dired-clean-directory} (@kbd{.}) command.  No one wants to save
too many versions of a file, since that takes up too much disk space.
The variable @code{kept-old-versions} tells the system how many of the
oldest versions to keep; and the variable @code{kept-new-versions} tells
the system how many new versions to keep.  The defaults values are two
old versions and two new.  Thus, if you had made a total of 77 versions
of @file{foo}, your directory would contain @file{foo.~1~},
@file{foo.~2~}, @file{foo.~75~}, @file{foo.~76~}, and @file{foo}, the
current version.

  If the value of the @code{trim-versions-without-asking} variable is
@code{nil}, the system queries the user before deleting excess versions.
Otherwise it does it silently.
@end deffn

@deffn Command save-buffers-kill-emacs &optional kill-silently-p 
@comment !!SourceFile files.el
  This function offers to save each buffer that needs to be saved, and
then kills this Emacs session.  Called with a non-@code{nil} value of
the optional @var{kill-silently-p} argument, this function saves all
the file-visiting buffers without querying the user or displaying any
message about saving, and then kills the session.

The body of the @code{save-buffers-kill-emacs} function consists of
the two following lines:

@example
(save-some-buffers arg t)
(kill-emacs)
@end example

@end deffn

@deffn Command save-some-buffers &optional save-silently-p exiting
  This command saves some modified file-visiting buffers.  Normally,
Emacs asks the user about each buffer.  If the function is called with a
non-@code{nil} value of the optional @var{save-silently-p} argument,
this function saves all the file-visiting buffers without querying the
user.

  The optional @var{exiting} argument is for non-interactive use only;
it is set by the @code{save-buffers-kill-emacs} function and causes
Emacs to offer to save even certain buffers that are not visiting files,
as well.  These are buffers that have a non-@code{nil} local value of
@code{buffer-offer-save}.
@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
  This function writes the current buffer into file @var{filename},
makes the buffer visit that file, and marks it not modified.
@end deffn

@defvar write-file-hooks
  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 are
not called, nor is the usual code for writing the file executed.

  If the @code{file-precious-flag} variable is @code{nil}, the file is
moved to the backup file before any of the hooks are called, so if
none of the hooks save the file, but one returns non-@code{nil}, the
file will not exist, although the backup will.

  Here is an example of how to add a hook to the @code{write-file-hooks}
just once.

@example
(or (memq 'my-write-file-hook write-file-hooks)
    (setq write-file-hooks 
          (cons 'my-write-file-hook write-file-hooks)))
@end example
@end defvar

@defvar file-precious-flag
  If this global variable is non-@code{nil}, then @code{save-buffer}
protects against I/O errors while saving files, by renaming the original file
to a temporary name before writing the new contents of the file.
If the new contents are successfully written, the renamed original file
is deleted.  Otherwise, it is renamed back to the original name.
This procedure prevents problems such as a lack of disk space from
resulting in an invalid file.

Some modes set this non-@code{nil} locally in particular buffers.
@end defvar

@defopt require-final-newline
  This global variable determines whether files may be written out
that do @emph{not} end with a newline.  If the value of the variable
is @code{t}, then Emacs silently puts a newline at the end of the file
whenever the file being saved does not already end in one.  If the
value of the variable is non-@code{nil}, but not @code{t}, then Emacs
asks the user whether to add a newline in each such case.

  If the value of the variable is @code{nil}, then Emacs doesn't add
newlines at all.  @code{nil} is the default value, but a few major modes
change it to @code{t}.
@end defopt

@node Reading from Files, Writing to Files, Saving Buffers, Files
@comment  node-name,  next,  previous,  up
@section Reading from Files

  You can copy a file directly from the disk and insert it into a buffer
using the @code{insert-file-contents} function, or its interactive
envelope, @code{insert-file}.

@deffn Command insert-file filename
  This function inserts the contents of file @var{filename} into the
current buffer after the point.  It is an error if @var{filename} is not
a readable file.  This is for interactive use and does little more than
call @code{insert-file-contents}.
@end deffn

@defun insert-file-contents filename visit
  This function inserts the contents of file @var{filename} into the current
buffer after the point.  If @var{visit} is non-@code{nil}, the buffer's
visited filename and last save file modtime are set, and it is marked
unmodified, so that it is now visiting the file @var{filename}.

  It is an error if @var{filename} is not a readable file.

  This function returns a list of the absolute file name and the length
of the data inserted.
@end defun

@node Writing to Files, File Locks, Reading from Files, Files
@comment  node-name,  next,  previous,  up
@section Writing to Files

  You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the @code{append-to-file} and
@code{write-region} functions.  Normally, this is done for files not
visited by the buffer in question.

@deffn Command append-to-file start end filename
  This function appends the contents of the region delimited by
@var{start} and @var{end} in the current buffer to the end of file
@var{filename}.  If that file does not exist, it is created.

  This function returns @code{nil}.

  It is an error if @var{filename} does not specify a (possibly non-existent)
file which is writable in an existing directory.  
@end deffn

@deffn Command write-region start end filename &optional append visit
This function writes the region (of the current buffer) delimited by
@var{start} and @var{end} into the file specified by @var{filename}.

If @var{append} is non-@code{nil}, then the region will be appended to the
existing file contents (if any).

If @var{visit} is @code{t}, then Emacs establishes an association
between the buffer and the file: the buffer is then visiting that file.
It also sets the last file modification time for the current buffer to
@var{filename}'s modtime, and marks the buffer as not modified.

Normally, this function prints a message @samp{Wrote file @var{filename}}
in the echo area.  If @var{visit} is neither @code{t} nor @code{nil}, then
this message is inhibited.  This feature is useful for programs which use
files for internal purposes, files which the user does not need to know
about.
@end deffn

@node File Locks, Information about Files, Writing to Files, Files
@section File Locks
@cindex file locks

  When two different people attempt to modify and save the same file at
the same time, the changes made by one person are lost as the changes
made by the other overwrite them.  File locks are used to help avoid
such an unfortunate occurrence.  Instead of destroying on person's work,
Emacs, aided by locks, will ask you what to do.

@defun file-locked-p filename
  This function returns @code{nil} if the @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.

@example
(file-locked-p "foo")
     @result{} nil
@end example
@end defun

@defun lock-buffer &optional filename
  This function locks @var{filename}, if the current buffer is modified.
@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.
@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.
@end defun

@defun ask-user-about-lock file other-user
  This function asks the user what to do when he or she has asked to
edit @var{file} but it is locked by @var{other-user}.

@cindex file-locked error
  Depending on the user's answer, the @code{ask-user-about-lock}
function will do one of the following:

@itemize @bullet
@item
The function may return @code{t}, which grabs the lock on the file; in
this case the user may edit the file; and it becomes locked to
@var{other-user}.

@item
The function may return @code{nil}, which allows the user to edit the
file even though it is locked.

@item
The function may signal a @code{file-locked} error, in which case the
user is refraining from editing the file.  In this case, Emacs
displays the following error message:

@example
@error{} "File is locked" @var{file} @var{other-user}
@end example

@noindent
where @code{file} is the name of the file and @var{other-user} is the
name of the user who has locked the file.
@end itemize

  If you wish, you can replace the @code{ask-user-about-lock} function
with your own version that does what you prefer.  The code for its usual
definition is in @file{userlock.el}.
@end defun

@node Information about Files, Contents of Directories, File Locks, 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
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{../}).  Environment variables in
filenames, such as @code{$HOME}, etc., are not substituted by these
functions.

@menu
* Testing Accessibility::	
* Distinguishing Kinds of Files::	
* File Attributes::	
@end menu

@node Testing Accessibility, Distinguishing Kinds of Files, Information about Files, Information about Files
@comment  node-name,  next,  previous,  up
@subsection Testing Accessibility

@defun file-exists-p filename
  This function returns @code{t} if a file named @var{filename} exists.
This does not mean you can necessarily read the file, only that you can
do a directory listing on the directory which it is in.

  If you do not have permission to do a directory listing on the directory
containing @var{filename}, then the result will be @code{nil}.
@end defun

@defun file-readable-p filename
  This function returns @code{t} if a file named @var{filename} exists
and you can read it.  It returns @code{nil} otherwise.

@example
(file-readable-p "file.texinfo")
     @result{} t
(file-exists-p "/usr/spool/mqueue")
     @result{} t
(file-readable-p "/usr/spool/mqueue")
     @result{} nil
@end example
@end defun

@defun file-writable-p filename
  This functions returns @code{t} if @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 directory it would be in
does exist and you can write in that directory.
@code{file-writable-p} returns @code{nil} otherwise.

  In the third example below, @code{foo} is not writable because the parent
directory does not exist, even though the user could create it.

@example
(file-writable-p "~rms/foo")
     @result{} t
(file-writable-p "/foo")
     @result{} nil
(file-writable-p "~rms/no-such-dir/foo")
     @result{} nil
@end example
@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
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}.

  In the 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.

@example
(file-newer-than-file-p "aug-19" "aug-20")
     @result{} nil
(file-newer-than-file-p "aug-20" "aug-19")
     @result{} t
(file-newer-than-file-p "aug-19" "no-file")
     @result{} t
(file-newer-than-file-p "no-file" "aug-19")
     @result{} nil
@end example
@end defun

@node Distinguishing Kinds of Files, File Attributes, Testing Accessibility, Information about Files
@comment  node-name,  next,  previous,  up
@subsection Distinguishing Kinds of Files
@defun file-symlink-p filename
@cindex file symbolic links

  If @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 @var{filename} is not a symbolic link (or there is no such file),
@code{file-symlink-p} returns @code{nil}.  

@example
(file-symlink-p "foo")
     @result{} nil
(file-symlink-p "sym-link")
     @result{} "foo"
(file-symlink-p "sym-link2")
     @result{} "sym-link"
(file-symlink-p "/bin")
     @result{} "/pub/bin"
@end example

@c !!! file-symlink-p: should show output of ls -l for comparison
@end defun

@defun file-directory-p filename
  This function returns @code{t} if @var{filename} is the name of an
existing directory, @code{nil} otherwise.

@example
(file-directory-p "~rms")
     @result{} t
(file-directory-p "~rms/lewis/file.texinfo")
     @result{} nil
(file-directory-p "~rms/lewis/no-such-file")
     @result{} nil
(file-directory-p "$HOME")
     @result{} nil
(file-directory-p (substitute-in-file-name "$HOME"))
     @result{} t
@end example
@end defun

@node File Attributes,  , Distinguishing Kinds of Files, Information about Files
@comment  node-name,  next,  previous,  up
@subsection Other Information about Files

@defun file-attributes filename
  This function returns a list of attributes of file @var{filename}.  If
the specified file cannot be opened, it returns @code{nil}.

  The elements of the list, in order, are:
@enumerate
@item
@code{t} for a directory, a string for a symbolic link (the name
linked to), or @code{nil} for a text file.

@item
The number of links to the file.

@item
The file's @sc{uid}.

@item
The file's @sc{gid}.

@item
The time of last access, as a list of two integers.
The first integer has the high-order 16 bits of time,
the second has the low 16 bits.

@item
The time of last modification as a list of two integers (see above).

@item
The time of last status change as a list of two integers (see above).

@item
The size of the file in bytes.

@item
The file's modes, as a string of ten letters or dashes
as in @code{ls -l}.

@item
@code{t} if the file's @sc{gid} would change if file were
deleted and recreated.

@item
The file's inode number.
@end enumerate

For example, here are the file attributes for @file{file.texinfo}:

@example
(file-attributes "file.texinfo")
     @result{}  (nil 
                1 
                2235 
                75 
                (8489 20284) 
                (8489 20284) 
                (8489 20285)
                14906 
                "-rw-rw-rw-" 
                nil 
                20920)
@end example

@noindent
and here is how the result is interpreted:

@table @code
@item nil
is neither a directory nor a symbolic link.

@item 1
has only one link to it, the name @file{file.texinfo}.

@item 2235
is owned by the user with @sc{uid} 2235.

@item 75
is in the group with @sc{gid} 75

@item (8489 20284)
was last accessed on Aug 19 00:09.  Unfortunately, you cannot convert
this number into a time string in Emacs.

@item (8489 20284)
was last accessed on Aug 19 00:09.  Unfortunately, you cannot convert
this number into a time string in Emacs.

@item (8489 20285
last had its inode changed on Aug 19 00:09.  Unfortunately, you cannot
convert this number into a time string in Emacs.

@item 14906
has 14906 characters in it.

@item -rw-rw-rw-
has a mode of read and write access for the owner, group, and world.

@item nil
would retain the same @file{gid} if it were recreated.

@item 20920
has an inode number of 20920
@end table
@end defun

@defun file-modes file-name
@cindex permission
@cindex file attributes

  This function returns the mode bits of @var{file-name}, as a decimal
integer.  The mode bits are the usual Unix mode bits.  If the
low-order bit is 1, then the file is executable by others, if the
second lowest-order bit is 1, then the file is writable by others,
etc.

  The highest value returnable is 4095 (7777 octal), meaning that everyone
has read, write, and execute permission, that the file has the @sc{suid} bit
set for both others and group, and that the file has the sticky bit set.

@example
(file-modes "~/junk/diffs")
     @result{} 492               ; @r{decimal integer}
(format "%o" 492)
     @print{} 754               ; @r{convert to octal}

(set-file-modes "~/junk/diffs" 4095)
     @result{} nil

% ls -l diffs
     @result{} -rwxr-xr--  1 lewis    0    3063 Oct 30 16:00 diffs
@end example
@end defun

@defun file-nlinks filename
@cindex file hard links
  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 returns @code{nil}.

@example
% ls -l foo*
  -rw-rw-rw-  2 rms             4 Aug 19 01:27 foo
  -rw-rw-rw-  2 rms             4 Aug 19 01:27 foo1

(file-nlinks "foo")
     @result{} 2
(file-nlinks "doesnt-exist")
     @result{} nil
@end example
@end defun

@node Contents of Directories, Changing File Names and Attributes, Information about Files, Files
@section Contents of Directories
@cindex directory-oriented functions
@cindex file names in directory

  A directory is a kind of file which contains other files entered under
various names.  Directories belong to Unix, not to Emacs.

  Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the @code{ls} shell command.  In
the latter case, Emacs will display information about each file,
depending on the value of switches passed to the @code{ls} command.

@defun directory-files directory &optional full-name match-regexp
  This function returns a list of the names of the files in the directory
@var{directory}.

If @var{full-name} is non-@code{nil}, the function returns the files'
absolute file names.  Otherwise, if @var{match-regexp} is non-@code{nil},
function returns only those file names that contain that regular
expression---the other file names are discarded from the list.

@example
(directory-files "~lewis")
     @result{} ("#foo#" "#foo.el#" "." ".."
    "dired-mods.el" "file.texinfo" "file.texinfo.~1~")
@end example

  It is an error if @var{directory} is not the name of a readable
directory.
@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}.
@end defun

@deffn Command list-directory dirname &optional verbose
@pindex ls
  This command displays a list of files in or matching @var{dirname}.
It calls the shell command @code{ls}, optionally passing it an
appropriate switch.

Wildcards in @var{dirname} are processed by the
shell.  

A prefix argument (the function's second argument if it is called
noninteractively) causes the function to pass the value of
@code{list-directory-verbose-switches} to @code{ls} as a switch.
Otherwise, the function passes @code{list-directory-brief-switches} to
@code{ls}.
@end deffn

@defvar list-directory-brief-switches
  This variable contains switches for @code{list-directory} to pass to
@code{ls} for a short or `brief' listing.  The default value is
@code{"-CF"}.
@end defvar

@defvar list-directory-verbose-switches
  This variable contains switches for @code{list-directory} to pass to
@code{ls} for a verbose or `long' listing.  The default value is
@code{"-l"}.
@end defvar

@defvar default-directory
  The value of this buffer-local variable is the default directory
for the current buffer.  This is always a string ending with a slash
on Unix systems.

@example
default-directory
     @result{} "/user/lewis/manual/"
@end example
@end defvar

@node Changing File Names and Attributes, File Names, Contents of Directories, Files
@section Changing File Names and Attributes
@cindex renaming files in file system
@cindex copying files in file system
@cindex deleting files in file system
@cindex linking files in file system
@cindex setting modes of files

  You can use the functions in this section to rename, copy, delete,
link, and set the modes of files.

@defun add-name-to-file oldname newname &optional ok-if-already-exists
@cindex file hard link
  This function gives the file named @var{oldname} the additional name
@var{newname}.  This means that @var{newname} will be a new ``hard
link'' to @var{oldname}.

  This function is meaningless on VMS, where multiple names for one file
are not allowed.

  If a file by the name of @var{newname} already exists:

@itemize @bullet

@item
It is an error if @var{ok-if-already-exists} is  @code{nil}.

@item
Confirmation is requested if @var{ok-if-already-exists} is a number.

@item
No confirmation is requested if @var{ok-if-already-exists} is any other
value, in which case the old file is removed.
@end itemize

  In the first part of the following example, we list two files,
@file{foo} and @file{foo3}.

@example
% 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
@end example

Then we evaluate the form @code{(add-name-to-file "~/lewis/foo"
"~/lewis/foo2")}.  Again we list the files.  This shows two links to
@file{foo} and @file{foo2}.

@example
(add-name-to-file "~/lewis/foo1" "~/lewis/foo2")
     @result{} nil

% 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
@end example

  Finally, we evaluate @code{(add-name-to-file "~/lewis/foo"
"~/lewis/foo3" t)}, and again list the files.  Now there are three
links to @file{foo}, @file{foo2}, and @file{foo3}).  The old contents
of @file{foo3} are lost.

@example
(add-name-to-file "~/lewis/foo1" "~/lewis/foo3")
     @result{} nil

% 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
@end example
@end defun

@deffn Command rename-file filename newname &optional ok-if-already-exists
@pindex mv
  This function renames @var{filename} as @var{newname}.

@cindex file-already-exists error
  If @var{filename} has names (i.e., hard links) other than filename,
it continues to have those names.  

If a file by the name of @var{newname} already exists:

@itemize @bullet
@item
The function signals a @code{file-already-exists} error, unless
@var{ok-if-already-exists} is non-@code{nil}.

@item
Emacs requests confirmation if @var{newname} already exists if
@var{ok-if-already-exists} is numeric.
@end itemize

  When called interactively, Emacs prompts for @var{filename} and
@var{newname} in the minibuffer.  In interactive use, Emacs requests
confirmation if @var{newname} already exists.
@end deffn

@defun copy-file oldname newname &optional ok-if-exists time
@pindex cp
  This function copies the file @var{oldname} to @var{newname}.  It is
an error if @var{oldname} does not exist.

  If a file by the name of @var{newname} already exists:

@itemize @bullet

@item
It is an error if  @var{ok-if-exists} is either @code{nil} or not supplied.

@item
Emacs requests confirmation if @var{ok-if-exists} is a number.

@item
Emacs does @emph{not} request confirmation if @var{ok-if-exists} is
any other value, in which case the old file is removed.
@end itemize

  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.)
@end defun

@defun delete-file filename
@pindex rm
  This function deletes the file @var{filename}.  This function
is essentially the same as the shell command @samp{rm @var{filename}}.

  If @var{filename} has multiple names, it continues to exist with the
other names.

  It is an error if the file does not exist, or is not deletable.  (In
Unix, a file is deletable if it is writable or its directory is
writable.)
@end defun

@deffn Command make-symbolic-link filename newname  &optional ok-if-exists
@pindex ln
@cindex file-already-exists error
  This function makes a symbolic link to @var{filename}, named
@var{newname}.  It signals a @code{file-already-exists} error if
@var{newname} already exists unless @var{ok-if-exists} is
non-@code{nil}.  If @var{ok-if-exists} is numeric, then Emacs requests
confirmation if @var{newname} already exists.  If it is @code{t}, then
the old file is simply deleted.

  When called interactively, @var{filename} and @var{newname} are prompted
for in the minibuffer.  @var{ok-if-exists} is set to the processed prefix
argument.
@end deffn

@defun set-file-modes file-name mode
@pindex chmod
  This function sets mode bits of @var{file-name} to @var{mode} (which must
be a integer).  Only the 12 low bits of @var{mode} are used.
@end defun

@node File Names,  , Changing File Names and Attributes, Files
@section File Names
@cindex file names

  Files are generally referred to by their names; Emacs is no exception
to this.  File names in Emacs are represented as strings.  The functions
which read, write or move files all expect a file name argument.

  In addition to operating on files themselves, Emacs Lisp programs often
need to operate on the names: to take them apart, and use the pieces
to construct related file names.  This section describes how to manipulate
file names.

  The functions in this section do not actually operate on files, so
they can operate on file names which 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 then work properly on either
system without change.

@ignore
This is a very obscure function which has only an indirect relationship
with the topic of the section.  Of all functions to put at the beginning
of the section, this is the worst one.

@defun define-logical-name varname string
  This function defines the logical name @var{name} to have the value
@var{string}.  It is available only on VMS.
@end defun
@end ignore

@node File Name Components, Directory Names,  , File Names
@subsection File Name Components

  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 directory name, and @dfn{nondirectory} part or file name within the
directory.  Concatenating these two parts reproduces the original file
name.  Either part may be empty.  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.

  For some purposes, the nondirectory part is further subdivided into
the name and the 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.

@defun file-name-directory filename
  This function returns the directory component in
@var{filename}.  It returns @code{nil} if @var{filename} does
not include a directory.  On Unix, the function returns a string ending in
a slash.  On VMS, it returns a string ending in one of the three
characters @samp{:}, @samp{]}, or @samp{>}.

@example
(file-name-directory "lewis/foo")     ; @r{Unix example}
     @result{} "lewis/"
(file-name-directory "foo")           ; @r{Unix example}
     @result{} nil
(file-name-directory "[X]FOO.TMP")    ; @r{VMS example}
     @result{} [X]
@end example
@end defun

@defun file-name-nondirectory filename
  This function returns the file name from @var{filename} without
its directory component (if any).

@example
(file-name-nondirectory "lewis/foo")
     @result{} "foo"
(file-name-nondirectory "foo")
     @result{} "foo"
(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.

@example
(file-name-sans-versions "~rms/foo.~1~")
     @result{} "~rms/foo"
(file-name-sans-versions "~rms/foo~")
     @result{} "~rms/foo"
(file-name-sans-versions "~rms/foo")
     @result{} "~rms/foo"
;; @r{The following example applies to VMS only.}
(file-name-sans-versions "foo;23")
     @result{} "foo"
@end example
@end defun

@node Directory Names, Relative File Names, File Name Components, File Names
@comment  node-name,  next,  previous,  up
@subsection Directory Names

  A directory name is the name of a directory, which is a special kind of
file.  This file also has a file name, which is its name when considered
as a file in its own right.  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.  (This is not quite identical to the conventions of
Unix terminology.)  On VMS, the relationship is more complicated.

  Though the difference between a directory name and its name as a file
may be small, it is crucial.  When an Emacs variable or function argument
is described as being a directory name, a file name of a directory is
not acceptable.

  All of these functions take a single argument, @var{filename}, which
must be a string.  Environment variables such as @samp{$HOME}, and the
symbols @samp{~}, and @samp{..}, are @emph{not} expanded.  Use
@code{expand-file-name} or @code{substitute-in-file-name} for that
(@pxref{Relative File Names}).

@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 that the string has a slash appended to it.  In
VMS, the function converts a string of the form @file{[X]Y.DIR.1} to
the form @file{[X.Y]}.

@example
(file-name-as-directory "~rms/lewis")
     @result{} "~rms/lewis/"
@end example
@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 that the string has a final slash removed.  On VMS, the
function converts a string of the form @file{[X.Y]} to
@file{[X]Y.DIR.1}.

@example
(directory-file-name "~lewis/")
     @result{} "~lewis"
@end example
@end defun

@node Relative File Names, File Name Expansion, Directory Names, File Names
@subsection Absolute and Relative File Names

  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 an @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
@cindex absolute file name
  This function returns @code{t} if file @var{filename} specifies an absolute
file name, @code{nil} otherwise.  On VMS, this function understands both
Unix syntax and VMS syntax.

@example
(file-name-absolute-p "~rms/foo")
     @result{} t
(file-name-absolute-p "rms/foo")
     @result{} nil
(file-name-absolute-p "$HOME")
     @result{} nil
(file-name-absolute-p "/user/rms/foo")
     @result{} t
@end example
@end defun

@node File Name Expansion, Unique File Names, Relative File Names, File Names
@subsection Functions that Expand Filenames
@cindex expansion of file names

  @dfn{Expanding} a file name means converting a relative file name
to an absolute one.  Since this is done relative to a directory,
you must specify the directory name as well as the file name to be
expanded.

  Expansion also canonicalizes file names by simplifying redundancies
such as @file{./} and @file{@var{name}/../}.

@defun expand-file-name filename &optional directory
  This function converts @var{filename} to an absolute file name.  If
@var{directory} is supplied, then it is the directory to start with if
@var{filename} is relative.  Otherwise, the current buffer's value of
@code{default-directory} is used.

  Filenames containing @samp{.} or @samp{..} are expanded to their
canonical form.  Adjacent @samp{/}s condensed into a single @samp{/}.
@samp{~} as a file is expanded into the user's home directory.  See
@code{substitute-in-file-name} below for the details.  

  But note that @code{expand-file-name} does @emph{not} expand
environment variables.  (@code{substitute-in-file-name} does that.)

@example
(expand-file-name "foo")
     @result{} "/xcssun/users/rms/lewis/foo"
(expand-file-name "../foo")
     @result{} "/xcssun/users/rms/foo"
(expand-file-name "foo" "/usr/spool")
     @result{} "/usr/spool/foo"
(expand-file-name "$HOME/foo")
     @result{} "/xcssun/users/rms/lewis/$HOME/foo"
@end example
@end defun

@defun substitute-in-file-name  filename
  This function replaces environment variables names in @var{filename}
with the values to which they are set by the operating system.
Following standard Unix shell syntax, @samp{$} begins an environment
variable.

  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{@}}.

If a @samp{~} or a @samp{/} appears following a @samp{/}, everything
through the first @samp{/} is discarded.

Here we assume that the environment variable @code{HOME}, which is the
user's home directory name, is @samp{/xcssun/users/rms}.

@example
(substitute-in-file-name "bar/~/foo")
     @result{} "~/foo"
(substitute-in-file-name "$HOME/foo")
     @result{} "/xcssun/users/rms/foo"
(substitute-in-file-name "/usr/local/$HOME/foo")
     @result{} "/xcssun/users/rms/foo"
@end example

On VMS, @samp{$} substitution is not done; this function does little on
VMS.
@end defun

@node Unique File Names, Filename Completion, File Name Expansion, File Names
@subsection Generating Unique File Names

  Some programs need to construct temporary files.  Here is the usual way to
construct a name for such a file:

@example
(concat "/tmp/" (make-temp-name @var{name-of-application}))
@end example

@noindent
The directory @file{/tmp/} is chosen because that is the standard place
on Unix for temporary files.  The task 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 will start with the prefix @var{string}, and finish with
a number which is different in each Emacs job.

@example
(make-temp-name "foo")
     @result{} "foo021304"
(make-temp-name "foo")
     @result{} "foo021304"
@end example

To prevent conflicts among different application libraries run in the
same Emacs, each application should have its own @var{string}.  The
number added to the end of the name distinguishes between the same
application running in different Emacses.
@end defun

@node Filename Completion,  , Unique File Names, File Names
@subsection Filename Completion
@cindex filename completion subroutines
@cindex completion, filename

  This section describes low-level subroutines for completing a filename.

   For other completion functions, @pxref{Completion}, and @pxref{Lisp
Symbol Completion}.

@defun file-name-all-completions partial-filename directory
  This function returns a list of all possible completions for a file
whose name starts with @var{partial-filename} in directory
@var{directory}.  The order of the completions is the order of the files
in @var{directory}, which is not normally sorted.

  @var{partial-filename} must contain no directory and no slash.  The current
buffer's default directory is prepended to @var{directory}, if
@var{directory} is not an absolute file name.

  In the following example, suppose that the current default
directory, @file{~rms/lewis}, has five files whose names begin with
@samp{f}: @file{foo}, @file{file~}, @file{file.texinfo},
@file{file.texinfo.~1~}, and @file{file.texinfo.~2~}.

@example
(file-name-all-completions "f" "~rms/lewis")
     @result{} ("foo" "file~" "file.texinfo.~2~" 
           "file.texinfo.~1~" "file.texinfo")

(file-name-all-completions "fo" "")  
     @result{} ("foo")
@end example
@end defun

@defun file-name-completion filename directory
  This function completes the file name @var{filename} in directory
@var{directory}.  It returns the longest prefix common to all filenames
in @var{directory} that start with @var{filename}.

  If only one match exists, and @var{filename} matches exactly, the
function returns @code{t}.  The function returns @code{nil} if
@var{directory} contains no name starting with @var{filename}.

  In the following example, suppose that the current default
direction, @file{~rms/lewis}, has five files whose names begin with
@samp{f}: @file{foo}, @file{file~}, @file{file.texinfo},
@file{file.texinfo.~1~}, and @file{file.texinfo.~2~}.

@example
(file-name-completion "fi" "")
     @result{} "file"

(file-name-completion "file.texinfo.~1" "")
     @result{} "file.texinfo.~1~"

(file-name-completion "file.texinfo.~1~" "")
     @result{} t

(file-name-completion "file.texinfo.~3" "")
     @result{} nil
@end example
@end defun

@defopt completion-ignored-extensions
  The filename completion functions usually ignore all filenames that
end in any string in this list.

  The variable looks somewhat like this:

@example
completion-ignored-extensions
     @result{} (".o" ".elc" "~" ".dvi")
@end example
@end defopt
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