In Emacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of Emacs Lisp, but a few others are described in section Buffers, and those related to backups and auto-saving are described in section 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 using expand-file-name, so that
`~' is handled correctly, as are relative file names (including
`../'). These functions don't recognize environment variable
substitutions such as `$HOME'. See section Functions that Expand Filenames.
Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file "the visited file" of the buffer.
A file and a buffer are two different things. 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; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file.
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 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.
This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with `find-' rather than `visit-'. See section Buffer File Name, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name.
The body of the find-file function is very simple and looks
like this:
(switch-to-buffer (find-file-noselect filename))
(See switch-to-buffer in section Displaying Buffers in Windows.)
When find-file is called interactively, it prompts for
filename in the minibuffer.
When 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
`yes', any changes previously made in the buffer are lost.
If find-file-noselect needs to create a buffer, and there is no
file named filename, it displays the message `New file' in
the echo area, and leaves the buffer empty.
The find-file-noselect function calls after-find-file
after reading the file (see section 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 find-file-hooks.
The find-file-noselect function returns the buffer that is
visiting the file filename.
(find-file-noselect "/etc/fstab")
=> #<buffer fstab>
When this command is called interactively, it prompts for filename.
When this command is called interactively, it prompts for filename.
find-file, but it marks the buffer as read-only. See section Read-Only Buffers, for related functions and variables.
When this command is called interactively, it prompts for filename.
view-mode-hook. See section Hooks.
When view-file is called interactively, it prompts for
filename.
This variable works just like a normal hook, but we think that renaming it would not be advisable.
find-file or find-file-noselect is passed a nonexistent
file name. find-file-noselect calls these functions as soon as
it detects a nonexistent file. It calls them in the order of the list,
until one of them returns non-nil. buffer-file-name is
already set up.
This is not a normal hook because the values of the functions are used and they may not all be called.
The find-file-noselect function uses the
create-file-buffer and after-find-file functions as
subroutines. Sometimes it is useful to call them directly.
Please note: create-file-buffer does not
associate the new buffer with a file and does not select the buffer.
(create-file-buffer "foo")
=> #<buffer foo>
(create-file-buffer "foo")
=> #<buffer foo<2>>
(create-file-buffer "foo")
=> #<buffer foo<3>>
This function is used by find-file-noselect.
It uses generate-new-buffer (see section Creating Buffers).
find-file-noselect
and by the default revert function (see section 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-nil value
for error. In that case, after-find-file issues a warning:
`(New File)'. For more serious errors, the caller should usually not
call after-find-file.
If warn is non-nil, then this function issues a warning
if an auto-save file exists and is more recent than the visited file.
The last thing after-find-file does is call all the functions
in find-file-hooks.
When you edit 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 edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.
save-buffer is responsible for making backup files. Normally,
backup-option is nil, and save-buffer makes a backup
file only if this is the first save since visiting the file. Other
values for backup-option request the making of backup files in
other circumstances:
save-buffer function marks this version of the file to be
backed up when the buffer is next saved.
save-buffer function unconditionally backs up the previous
version of the file before saving it.
nil, it saves all the file-visiting buffers without querying
the user.
The optional exiting argument, if non-nil, requests this
function to offer also to save certain other buffers that are not
visiting files. These are buffers that have a non-nil local
value of buffer-offer-save. (A user who says yes to saving one
of these is asked to specify a file name to use.) The
save-buffers-kill-emacs function passes a non-nil value
for this argument.
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 t.
set-visited-file-name and save-buffer.
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 write-file-hooks returns non-nil, it
is responsible for making a backup file (if that is appropriate).
To do so, execute the following code:
(or buffer-backed-up (backup-buffer))
You might wish to save the file modes value returned by
backup-buffer and use that to set the mode bits of the file that
you write. This is what save-buffer normally does.
Even though this is not a normal hook, you can use add-hook and
remove-hook to manipulate the list. See section Hooks.
write-file-hooks, but it is intended
to be made local to particular buffers. It's not a good idea to make
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.
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.
nil, then 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
the intended name after it is clear there are no errors. This procedure
prevents problems such as a lack of disk space from resulting in an
invalid file.
(This feature worked differently in older Emacs versions.)
Some modes set this non-nil locally in particular buffers.
t, then save-buffer silently adds a newline at the end of
the file whenever the buffer being saved does not already end in one.
If the value of the variable is non-nil, but not t, then
save-buffer asks the user whether to add a newline each time the
case arises.
If the value of the variable is nil, then save-buffer
doesn't add newlines at all. nil is the default value, but a few
major modes set it to t in particular buffers.
You can copy a file from the disk and insert it into a buffer
using the insert-file-contents function. Don't use the user-level
command insert-file in a Lisp program, as that sets the mark.
To set up saved text properties, insert-file-contents calls the
functions in the list after-insert-file-functions. For more
information, see section Saving Text Properites in Files.
If visit is non-nil, this function additionally marks the
buffer as unmodified and sets up various fields in the buffer so that it
is visiting the file filename: these include the buffer's visited
file name and its last save file modtime. This feature is used by
find-file-noselect and you probably should not use it yourself.
If beg and end are non-nil, they should be integers
specifying the portion of the file to insert. In this case, visit
must be nil. For example,
(insert-file-contents filename nil 0 500)
inserts the first 500 characters of a file.
If the argument replace is non-nil, it means to replace the
contents of the buffer (actually, just the accessible portion) with the
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.
If you want to pass a file name to another process so that another
program can read the file, use the function file-local-copy; see
section Making Certain File Names "Magic".
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the append-to-file and
write-region functions. Don't use these functions to write to
files that are being visited; that could cause confusion in the
mechanisms for visiting.
nil.
An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.
If start is a string, then write-region writes or appends
that string, rather than text from the buffer.
If append is non-nil, then the specified text is appended
to the existing file contents (if any).
If visit is t, then Emacs establishes an association
between the buffer and the file: the buffer is then visiting that file.
It also sets the last file modification time for the current buffer to
filename's modtime, and marks the buffer as not modified. This
feature is used by save-buffer, but you probably should not use
it yourself.
If visit is a string, it specifies the file name to visit. This
way, you can write the data to one file (filename) while recording
the buffer as visiting another file (visit). The argument
visit is used in the echo area message and also for file locking;
visit is stored in buffer-file-name. This feature is used
to implement file-precious-flag; don't use it yourself unless you
really know what you're doing.
To output information about text properties, write-region calls
the functions in the list write-region-annotation-functions. For
more information, see section Saving Text Properites in Files.
Normally, write-region displays a message `Wrote file
filename' in the echo area. If visit is neither t
nor nil nor a string, then this message is inhibited. This
feature is useful for programs that use files for internal purposes,
files that the user does not need to know about.
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 file lock when a file is being modified. 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.
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 section Comparison of Modification Time.
nil if the file filename is not
locked by this Emacs process. It returns 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.
(file-locked-p "foo")
=> nil
t says to grab the lock on the file. Then
this user may edit the file and other-user loses the lock.
nil says to ignore the lock and let this
user edit the file anyway.
file-locked error, in which
case the change that the user was about to make does not take place.
The error message for this error looks like this:
error--> File is locked: file other-userwhere
file is the name of the file and other-user is the
name of the user who has locked the file.
The default definition of this function asks the user to choose what
to do. If you wish, you can replace the ask-user-about-lock
function with your own version that decides in another way. The code
for its usual definition is in `userlock.el'.
The functions described in this section all operate on strings that designate file names. All the functions have names that begin with the word `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.
These functions test for permission to access a file in specific ways.
t if a file named 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.)
If the file does not exist, or if fascist access control policies
prevent you from finding the attributes of the file, this function
returns nil.
t if a file named filename exists
and you can read it. It returns nil otherwise.
(file-readable-p "files.texi")
=> t
(file-exists-p "/usr/spool/mqueue")
=> t
(file-readable-p "/usr/spool/mqueue")
=> nil
t if a file named filename exists and
you can execute it. It returns 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.
t if the file filename can be written
or created by you, and 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, `foo' is not writable because the parent directory does not exist, even though the user could create such a directory.
(file-writable-p "~/foo")
=> t
(file-writable-p "/foo")
=> nil
(file-writable-p "~/no-such-dir/foo")
=> nil
t if you have permission to open existing
files in the directory whose name as a file is dirname; otherwise
(or if there is no such directory), it returns nil. The value
of dirname may be either a directory name or the file name of a
directory.
Example: after the following,
(file-accessible-directory-p "/foo")
=> nil
we can deduce that any attempt to read a file in `/foo/' will give an error.
t if the file filename1 is
newer than file filename2. If filename1 does not
exist, it returns nil. If filename2 does not exist,
it returns t.
In the following example, assume that the file `aug-19' was written on the 19th, `aug-20' was written on the 20th, and the file `no-file' doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20")
=> nil
(file-newer-than-file-p "aug-20" "aug-19")
=> t
(file-newer-than-file-p "aug-19" "no-file")
=> t
(file-newer-than-file-p "no-file" "aug-19")
=> nil
You can use file-attributes to get a file's last modification
time as a list of two numbers. See section Other Information about Files.
This section describes how to distinguish directories and symbolic links from ordinary files.
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 it
may be a nonexistent file name.
If the file filename is not a symbolic link (or there is no such file),
file-symlink-p returns nil.
(file-symlink-p "foo")
=> nil
(file-symlink-p "sym-link")
=> "foo"
(file-symlink-p "sym-link2")
=> "sym-link"
(file-symlink-p "/bin")
=> "/pub/bin"
t if filename is the name of an
existing directory, nil otherwise.
(file-directory-p "~rms")
=> t
(file-directory-p "~rms/lewis/files.texi")
=> nil
(file-directory-p "~rms/lewis/no-such-file")
=> nil
(file-directory-p "$HOME")
=> nil
(file-directory-p
(substitute-in-file-name "$HOME"))
=> t
The truename of a file is the name that you get by following symbolic links until none remain, then expanding to get rid of `.' and `..' as components. Strictly speaking, a file need not 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.
file-truename returns the true name of the file
filename. This is the name that you get by following symbolic
links until none remain. The argument must be an absolute file name.
See section Buffer File Name, for related information.
This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.
The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the SUID bit is set for both others and group, and that the sticky bit is set.
(file-modes "~/junk/diffs")
=> 492 ; Decimal integer.
(format "%o" 492)
=> "754" ; Convert to octal.
(set-file-modes "~/junk/diffs" 438)
=> nil
(format "%o" 438)
=> "666" ; Convert to octal.
% ls -l diffs
-rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
nil. Note that symbolic links have no effect on this
function, because they are not considered to be names of the files they
link to.
% 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")
=> 2
(file-nlinks "doesnt-exist")
=> nil
nil.
The elements of the list, in order, are:
t for a directory, a string for a symbolic link (the name
linked to), or nil for a text file.
add-name-to-file function
(see section Changing File Names and Attributes).
current-time; see section Time of Day.)
t if the file's GID would change if file were
deleted and recreated; nil otherwise.
For example, here are the file attributes for `files.texi':
(file-attributes "files.texi")
=> (nil
1
2235
75
(8489 20284)
(8489 20284)
(8489 20285)
14906
"-rw-rw-rw-"
nil
129500
-32252)
and here is how the result is interpreted:
nil
1
2235
75
(8489 20284)
(8489 20284)
(8489 20285)
14906
"-rw-rw-rw-"
nil
129500
-32252
The functions in this section rename, copy, delete, link, and set the modes of files.
In the functions that have an argument newname, if a file by the name of newname already exists, the actions taken depend on the value of the argument ok-if-already-exists:
file-already-exists error if
ok-if-already-exists is nil.
In the first part of the following example, we list two files, `foo' and `foo3'.
% 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
Then we evaluate the form (add-name-to-file "~/lewis/foo"
"~/lewis/foo2"). Again we list the files. This shows two names,
`foo' and `foo2'.
(add-name-to-file "~/lewis/foo1" "~/lewis/foo2")
=> 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
Finally, we evaluate the following:
(add-name-to-file "~/lewis/foo" "~/lewis/foo3" t)
and list the files again. Now there are three names for one file: `foo', `foo2', and `foo3'. The old contents of `foo3' are lost.
(add-name-to-file "~/lewis/foo1" "~/lewis/foo3")
=> 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
This function is meaningless on VMS, where multiple names for one file are not allowed.
See also file-nlinks in section Other Information about Files.
If filename has additional names aside from filename, it
continues to have those names. In fact, adding the name newname
with add-name-to-file and then deleting filename has the
same effect as renaming, aside from momentary intermediate states.
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
If time is non-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.)
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
A suitable kind of 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.)
See also delete-directory in section Creating and Deleting Directories.
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
The argument mode must be an integer. Only the low 9 bits of mode are used.
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.
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 `.com',
`.bat' or `.exe'. This is reflected in the values returned
by file-modes and file-attributes.
Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that 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 part of a name to construct related file names. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they 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.
The operating system groups files into directories. To specify a 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 directory name part, and the nondirectory part (or 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.
For some purposes, the nondirectory part is further subdivided into the name proper 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.
nil if filename does not include a directory part). On
Unix, the function returns a string ending in a slash. On VMS, it
returns a string ending in one of the three characters `:',
`]', or `>'.
(file-name-directory "lewis/foo") ; Unix example
=> "lewis/"
(file-name-directory "foo") ; Unix example
=> nil
(file-name-directory "[X]FOO.TMP") ; VMS example
=> "[X]"
(file-name-nondirectory "lewis/foo")
=> "foo"
(file-name-nondirectory "foo")
=> "foo"
;; The following example is accurate only on VMS.
(file-name-nondirectory "[X]FOO.TMP")
=> "FOO.TMP"
(file-name-sans-versions "~rms/foo.~1~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo")
=> "~rms/foo"
;; The following example applies to VMS only.
(file-name-sans-versions "foo;23")
=> "foo"
A 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.
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.
The following two functions convert between directory names and file names. They do nothing special with environment variable substitutions such as `$HOME', and the constructs `~', and `..'.
(file-name-as-directory "~rms/lewis")
=> "~rms/lewis/"
(directory-file-name "~lewis/")
=> "~lewis"
Directory name abbreviations are useful for directories that are normally accessed through symbolic links. Sometimes the users recognize primarily the link's name as "the name" of the directory, and find it annoying to see the directory's "real" name. If you define the link name as an abbreviation for the "real" name, Emacs shows users the abbreviation instead.
directory-abbrev-alist contains an alist of
abbreviations to use for file directories. Each element has the form
(from . to), and says to replace from with
to when it appears in a directory name. The from string is
actually a regular expression; it should always start with `^'.
The function abbreviate-file-name performs these substitutions.
You can set this variable in `site-init.el' to describe the abbreviations appropriate for your site.
Here's an example, from a system on which file system `/home/fsf' and so on are normally accessed through symbolic links named `/fsf' and so on.
(("^/home/fsf" . "/fsf")
("^/home/gp" . "/gp")
("^/home/gd" . "/gd"))
To convert a directory name to its abbreviation, use this function:
directory-abbrev-alist
to its argument, and substitutes `~' for the user's home
directory.
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 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 relative file name. On Unix, an absolute file name starts with a slash or a tilde (`~'), and a relative one does not. The rules on VMS are complicated.
t if file filename is an absolute
file name, nil otherwise. On VMS, this function understands both
Unix syntax and VMS syntax.
(file-name-absolute-p "~rms/foo")
=> t
(file-name-absolute-p "rms/foo")
=> nil
(file-name-absolute-p "/user/rms/foo")
=> t
Expansion of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as `./' and `name/../'.
default-directory is
used. For example:
(expand-file-name "foo")
=> "/xcssun/users/rms/lewis/foo"
(expand-file-name "../foo")
=> "/xcssun/users/rms/foo"
(expand-file-name "foo" "/usr/spool/")
=> "/usr/spool/foo"
(expand-file-name "$HOME/foo")
=> "/xcssun/users/rms/lewis/$HOME/foo"
Filenames containing `.' or `..' are simplified to their canonical form:
(expand-file-name "bar/../foo")
=> "/xcssun/users/rms/lewis/foo"
`~/' is expanded into the user's home directory. A `/' or `~' following a `/' is taken to be the start of an absolute file name that overrides what precedes it, so everything before that `/' or `~' is deleted. For example:
(expand-file-name
"/a1/gnu//usr/local/lib/emacs/etc/MACHINES")
=> "/usr/local/lib/emacs/etc/MACHINES"
(expand-file-name "/a1/gnu/~/foo")
=> "/xcssun/users/rms/foo"
In both cases, `/a1/gnu/' is discarded because an absolute file name follows it.
Note that expand-file-name does not expand environment
variables; only substitute-in-file-name does that.
(file-relative-name "/foo/bar" "/foo/")
=> "bar")
(file-relative-name "/foo/bar" "/hack/")
=> "/foo/bar")
expand-file-name uses the default directory when its second
argument is nil.
On Unix systems, the value is always a string ending with a slash.
default-directory
=> "/user/lewis/manual/"
The environment variable name is the series of alphanumeric characters (including underscores) that follow the `$'. If the character following the `$' is a `{', then the variable name is everything up to the matching `}'.
Here we assume that the environment variable HOME, which holds
the user's home directory name, has value `/xcssun/users/rms'.
(substitute-in-file-name "$HOME/foo")
=> "/xcssun/users/rms/foo"
If a `~' or a `/' appears following a `/', after substitution, everything before the following `/' is discarded:
(substitute-in-file-name "bar/~/foo")
=> "~/foo"
(substitute-in-file-name "/usr/local/$HOME/foo")
=> "/xcssun/users/rms/foo"
On VMS, `$' substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.
Some programs need to write temporary files. Here is the usual way to construct a name for such a file:
(make-temp-name (concat "/tmp/" name-of-application))
Here we use the directory `/tmp/' because that is the standard
place on Unix for temporary files. The job of make-temp-name is
to prevent two different users or two different jobs from trying to use
the same name.
(make-temp-name "/tmp/foo")
=> "/tmp/foo021304"
To prevent conflicts among different libraries running in the same
Emacs, each Lisp program that uses make-temp-name should have its
own string. The number added to the end of the name distinguishes
between the same application running in different Emacs jobs.
This section describes low-level subroutines for completing a file name. For other completion functions, see section Completion.
The argument partial-filename must be a file name containing no directory part and no slash. The current buffer's default directory is prepended to directory, if directory is not absolute.
In the following example, suppose that the current default directory, `~rms/lewis', has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-all-completions "f" "")
=> ("foo" "file~" "file.c.~2~"
"file.c.~1~" "file.c")
(file-name-all-completions "fo" "")
=> ("foo")
If only one match exists and filename matches it exactly, the
function returns t. The function returns nil if directory
directory contains no name starting with filename.
In the following example, suppose that the current default directory has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-completion "fi" "")
=> "file"
(file-name-completion "file.c.~1" "")
=> "file.c.~1~"
(file-name-completion "file.c.~1~" "")
=> t
(file-name-completion "file.c.~3" "")
=> nil
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.
A typical value might look like this:
completion-ignored-extensions
=> (".o" ".elc" "~" ".dvi")
A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the ls shell command. In
the latter case, it can optionally display information about each file,
depending on the options passed to the ls command.
If full-name is non-nil, the function returns the files'
absolute file names. Otherwise, it returns the names relative to
the specified directory.
If match-regexp is non-nil, this function returns only
those file names that contain a match for that regular expression--the
other file names are excluded from the list.
If nosort is non-nil, directory-files does not sort
the list, so you get the file names in no particular order. Use this if
you want the utmost possible speed and don't care what order the files
are processed in. If the order of processing is visible to the user,
then the user will probably be happier if you do sort the names.
(directory-files "~lewis")
=> ("#foo#" "#foo.el#" "." ".."
"dired-mods.el" "files.texi"
"files.texi.~1~")
An error is signaled if directory is not the name of a directory that can be read.
ls according to
switches. It leaves point after the inserted text.
The argument file may be either a directory name or a file
specification including wildcard characters. If wildcard is
non-nil, that means treat file as a file specification with
wildcards.
If full-directory-p is non-nil, that means file is a
directory and switches do not contain `-d', so that the listing
should show the full contents of the directory. (The `-d' option
to ls says to describe a directory itself rather than its
contents.)
This function works by running a directory listing program whose name is
in the variable insert-directory-program. If wildcard is
non-nil, it also runs the shell specified by
shell-file-name, to expand the wildcards.
insert-directory.
delete-file does not work for files that are directories; you
must use delete-directory in that case.
You can implement special handling for certain file names. This is called making those names magic. 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 variable 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:
(regexp . handler)
All the Emacs primitives for file access and file name transformation
check the given file name against file-name-handler-alist. If
the file name matches regexp, the primitives handle that file by
calling handler.
The first argument given to 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:
(file-exists-p filename)
and filename has handler handler, then handler is called like this:
(funcall handler 'file-exists-p filename)
Here are the operations that a magic file name handler gets to handle:
add-name-to-file, copy-file, delete-directory,
delete-file,
directory-file-name,
diff-latest-backup-file, directory-files,
dired-compress-file, dired-uncache,
expand-file-name,
file-accessible-directory-p,
file-attributes, file-directory-p,
file-executable-p, file-exists-p, file-local-copy,
file-modes, file-name-all-completions,
file-name-as-directory, file-name-completion,
file-name-directory, file-name-nondirectory,
file-name-sans-versions, file-newer-than-file-p,
file-readable-p, file-symlink-p, file-truename,
file-writable-p, insert-directory,
insert-file-contents, load, make-directory,
make-symbolic-link, rename-file, set-file-modes,
set-visited-file-modtime, unhandled-file-name-directory,
verify-visited-file-modtime, write-region.
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:
(defun my-file-handler (operation &rest args)
;; First check for the specific operations
;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)
((eq operation 'write-region) ...)
...
;; Handle any operation we don't know about.
(t (let ((inhibit-file-name-handlers
(cons 'my-file-handler
(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))
(inhibit-file-name-operation operation))
(apply operation args)))))
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
inhibit-file-name-handlers and
inhibit-file-name-operation. Be careful to use them exactly as
shown above; the details are crucial for proper behavior in the case of
multiple handlers, and for operations that have two file names that may
each have handlers.
nil if there is none. The argument 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 inhibit-file-name-operation.
If 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.
If filename is an ordinary file name, not magic, then this function
does nothing and returns nil.
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.
Emacs on MS-DOS makes a distinction between text files and binary
files. This is necessary because ordinary text files on MS-DOS use a
two character sequence between lines: carriage-return and linefeed
(CRLF). 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
buffer-file-type for use when the file is saved.
See section MS-DOS Subprocesses, for a related feature for subprocesses.
nil for text,
t for binary.
nil for text, t for binary.
nil for text, 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 t or nil.
nil
for text, or t for binary.
find-file, but treat the file as text regardless of its name.
find-file, but treat the file as binary regardless of its
name.