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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 27. Buffers, and those related to backups and auto-saving are described in 26. 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 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 25.8.4 Functions that Expand Filenames.
When file I/O functions signal Lisp errors, they usually use the
condition file-error (see section 10.5.3.3 Writing Code to Handle Errors). The error
message is in most cases obtained from the operating system, according
to locale system-message-locale, and decoded using coding system
locale-coding-system (see section 33.12 Locales).
25.1 Visiting Files Reading files into Emacs buffers for editing. 25.2 Saving Buffers Writing changed buffers back into files. 25.3 Reading from Files Reading files into buffers without visiting. 25.4 Writing to Files Writing new files from parts of buffers. 25.5 File Locks Locking and unlocking files, to prevent simultaneous editing by two people. 25.6 Information about Files Testing existence, accessibility, size of files. 25.7 Changing File Names and Attributes Renaming files, changing protection, etc. 25.8 File Names Decomposing and expanding file names. 25.9 Contents of Directories Getting a list of the files in a directory. 25.10 Creating and Deleting Directories 25.11 Making Certain File Names "Magic" Defining "magic" special handling for certain file names. 25.12 File Format Conversion Conversion to and from various file formats.
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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.
25.1.1 Functions for Visiting Files The usual interface functions for visiting. 25.1.2 Subroutines of Visiting Lower-level subroutines that they use.
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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 27.4 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.
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 insert-file-contents in a
temporary buffer. Visiting the file is not necessary and takes longer.
See section 25.3 Reading from Files.
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 28.7 Displaying Buffers in Windows.)
If wildcards is non-nil, which is always true in an
interactive call, then find-file expands wildcard characters in
filename and visits all the matching files.
When find-file is called interactively, it prompts for
filename in the minibuffer.
If wildcards is non-nil,
then find-file-noselect expands wildcard
characters in filename and visits all the matching files.
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.
This function displays warning or advisory messages in various peculiar
cases, unless the optional argument nowarn is non-nil. For
example, if it 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 normally calls
after-find-file after reading the file (see section 25.1.2 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.
If the optional argument rawfile is non-nil, then
after-find-file is not called, and the
find-file-not-found-hooks are not run in case of failure. What's
more, a non-nil rawfile value suppresses coding system
conversion (see section 33.10 Coding Systems) and format conversion (see section 25.12 File Format Conversion).
The find-file-noselect function usually returns the buffer that
is visiting the file filename. But, if wildcards are actually
used and expanded, it returns a list of buffers that are visiting the
various files.
(find-file-noselect "/etc/fstab")
=> #<buffer fstab>
|
When this command is called interactively, it prompts for filename.
find-file, but it marks the buffer as read-only. See section 27.7 Read-Only Buffers, for related functions and variables.
When this command is called interactively, it prompts for filename.
view-mode-hook. See section 23.6 Hooks.
When view-file is called interactively, it prompts for
filename.
nil, then the various find-file
commands check for wildcard characters and visit all the files that
match them. If this is nil, then wildcard characters are
not treated specially.
This variable works just like a normal hook, but we think that renaming it would not be advisable. See section 23.6 Hooks.
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 in many cases only some of the functions are called.
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The find-file-noselect function uses two important subroutines
which are sometimes useful in user Lisp code: create-file-buffer
and after-find-file. This section explains how to use them.
Please note: create-file-buffer does not
associate the new buffer with a file and does not select the buffer.
It also does not use the default major mode.
(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 27.9 Creating Buffers).
find-file-noselect
and by the default revert function (see section 26.3 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.
If noauto is non-nil, that says not to enable or disable
Auto-Save mode. The mode remains enabled if it was enabled before.
If after-find-file-from-revert-buffer is non-nil, that
means this call was from revert-buffer. This has no direct
effect, but some mode functions and hook functions check the value
of this variable.
If nomodes is non-nil, that means don't alter the buffer's
major mode, don't process local variables specifications in the file,
and don't run find-file-hooks. This feature is used by
revert-buffer in some cases.
The last thing after-find-file does is call all the functions
in the list find-file-hooks.
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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 pred argument controls which buffers to ask about.
If it is nil, that means to ask only about file-visiting buffers.
If it is t, that means also offer to save certain other non-file
buffers--those that have a non-nil buffer-local value of
buffer-offer-save. (A user who says `yes' to saving a
non-file buffer is asked to specify the file name to use.) The
save-buffers-kill-emacs function passes the value t for
pred.
If pred is neither t nor 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-nil
value in a certain buffer, that means do offer to save that buffer.
set-visited-file-name (see section 27.4 Buffer File Name) and
save-buffer.
If confirm is non-nil, that means to ask for confirmation
before overwriting an existing file.
Saving a buffer runs several hooks. It also performs format conversion (see section 25.12 File Format Conversion), and may save text properties in "annotations" (see section 32.19.7 Saving Text Properties in Files).
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.
The hook functions in write-file-hooks are also responsible for
encoding the data (if desired): they must choose a suitable coding
system (see section 33.10.3 Coding Systems in Lisp), perform the encoding
(see section 33.10.7 Explicit Encoding and Decoding), and set last-coding-system-used to
the coding system that was used (see section 33.10.2 Encoding and I/O).
Do not make this variable buffer-local. To set up buffer-specific hook
functions, use write-contents-hooks instead.
Even though this is not a normal hook, you can use add-hook and
remove-hook to manipulate the list. See section 23.6 Hooks.
write-file-hooks, but it is intended to be
made buffer-local in particular buffers, and used for hooks that pertain
to the file name or the way the buffer contents were obtained.
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. 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. When you use
add-hooks to add an element to this hook, you should not
specify a non-nil local argument, since this variable is
used only buffer-locally.
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.
As a side effect, backups are necessarily made by copying. See section 26.1.2 Backup by Renaming or by Copying?. 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 give this variable a non-nil buffer-local value
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.
See also the function set-visited-file-name (see section 27.4 Buffer File Name).
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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.
The function insert-file-contents checks the file contents
against the defined file formats, and converts the file contents if
appropriate. See section 25.12 File Format Conversion. It also calls the functions in
the list after-insert-file-functions; see 32.19.7 Saving Text Properties in Files. Normally, one of the functions in the
after-insert-file-functions list determines the coding system
(see section 33.10 Coding Systems) used for decoding the file's contents.
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.
It is possible to read a special file (such as a FIFO or an I/O device)
with insert-file-contents, as long as replace and
visit are nil.
insert-file-contents except that it does
not do format decoding (see section 25.12 File Format Conversion), does not do
character code conversion (see section 33.10 Coding Systems), does not run
find-file-hooks, does not perform automatic uncompression, and so
on.
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
25.11 Making Certain File Names "Magic".
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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. end is ignored in
this case.
If append is non-nil, then the specified text is appended
to the existing file contents (if any). Starting in Emacs 21, if
append is an integer, then write-region seeks to that byte
offset from the start of the file and writes the data from there.
If mustbenew is non-nil, then write-region asks
for confirmation if filename names an existing file.
Starting in Emacs 21, if mustbenew is the symbol excl,
then write-region does not ask for confirmation, but instead
it signals an error file-already-exists if the file already
exists.
The test for an existing file, when mustbenew is 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 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.
The optional argument lockname, if non-nil, specifies the
file name to use for purposes of locking and unlocking, overriding
filename and visit for that purpose.
The function write-region converts the data which it writes to
the appropriate file formats specified by buffer-file-format.
See section 25.12 File Format Conversion. It also calls the functions in the list
write-region-annotate-functions; see 32.19.7 Saving Text Properties in Files.
Normally, write-region displays the message `Wrote
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.
with-temp-file macro evaluates the body forms with a
temporary buffer as the current buffer; then, at the end, it writes the
buffer contents into file file. It kills the temporary buffer
when finished, restoring the buffer that was current before the
with-temp-file form. Then it returns the value of the last form
in body.
The current buffer is restored even in case of an abnormal exit via
throw or error (see section 10.5 Nonlocal Exits).
See also with-temp-buffer in 27.2 The Current Buffer.
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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. 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.
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 27.6 Comparison of Modification Time.
nil if the file filename is not
locked. It returns 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.
(file-locked-p "foo")
=> nil
|
File locking is not supported on some systems. On systems that do not
support it, the functions lock-buffer, unlock-buffer and
file-locked-p do nothing and return 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-user |
where file is the name of the file and other-user is the
name of the user who has locked the file.
If you wish, you can replace the ask-user-about-lock function
with your own version that makes the decision in another way. The code
for its usual definition is in `userlock.el'.
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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.
25.6.1 Testing Accessibility Is a given file readable? Writable? 25.6.2 Distinguishing Kinds of Files Is it a directory? A symbolic link? 25.6.3 Truenames Eliminating symbolic links from a file name. 25.6.4 Other Information about Files How large is it? Any other names? Etc.
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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 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 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. 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.
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
file which is 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.
nil. However, if the open fails, it signals an error
using string as the error message text.
t if deleting the file filename and
then creating it anew would keep the file's owner unchanged.
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 25.6.4 Other Information about Files.
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This section describes how to distinguish various kinds of files, such as directories, symbolic links, and 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
|
t if the file filename exists and is
a regular file (not a directory, named pipe, terminal, or
other I/O device).
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The truename of a file is the name that you get by following symbolic links at all levels until none remain, then simplifying away `.' and `..' 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.
file-truename returns the truename of the file
filename. The argument must be an absolute file name.
To illustrate the difference between file-chase-links and
file-truename, suppose that `/usr/foo' is a symbolic link to
the directory `/home/foo', and `/home/foo/hello' is an
ordinary file (or at least, not a symbolic link) or nonexistent. Then
we would have:
(file-chase-links "/usr/foo/hello")
;; This does not follow the links in the parent directories.
=> "/usr/foo/hello"
(file-truename "/usr/foo/hello")
;; Assuming that `/home' is not a symbolic link.
=> "/home/foo/hello"
|
See section 27.4 Buffer File Name, for related information.
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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 25.7 Changing File Names and Attributes).
current-time; see 40.5 Time of Day.)
t if the file's GID would change if file were
deleted and recreated; nil otherwise.
(high . low), where low
holds the low 16 bits.
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
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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 -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 |
Now we create a hard link, by calling add-name-to-file, then list
the files again. This shows two names for one file, `foo' and
`foo2'.
(add-name-to-file "foo" "foo2")
=> nil
% 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
|
Finally, we evaluate the following:
(add-name-to-file "foo" "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 "foo1" "foo3")
=> nil
% 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
|
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 file-nlinks in 25.6.4 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 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,
copy-file signals a file-date-error error.
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 and GNU/Linux, a file is
deletable if its directory is writable.)
See also delete-directory in 25.10 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.
This function is not available on systems that don't support symbolic links.
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 mode must be an integer. On most systems, only the low 9 bits of mode are meaningful. You can use the Lisp construct for octal character codes to enter mode; for example,
(set-default-file-modes ?\644) |
Saving a modified version of an existing file does not count as creating the file; it preserves the existing file's mode, whatever that is. So the default file protection has no effect.
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 one of the
standard executable extensions, such as `.com', `.bat',
`.exe', and some others. Files that begin with the Unix-standard
`#!' signature, such as shell and Perl scripts, are also considered
as executable files. This is reflected in the values returned by
file-modes and file-attributes. Directories are also
reported with executable bit set, for compatibility with Unix.
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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 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.
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 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.
25.8.1 File Name Components The directory part of a file name, and the rest. 25.8.2 Directory Names A directory's name as a directory is different from its name as a file. 25.8.3 Absolute and Relative File Names Some file names are relative to a current directory. 25.8.4 Functions that Expand Filenames Converting relative file names to absolute ones. 25.8.5 Generating Unique File Names Generating names for temporary files. 25.8.6 File Name Completion Finding the completions for a given file name. 25.8.7 Standard File Names If your package uses a fixed file name, how to handle various operating systems simply.
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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 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 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.
nil if filename does not include a directory part). On
most systems, 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"
|
If keep-backup-version is non-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.
(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"
|
(file-name-sans-extension "foo.lose.c")
=> "foo.lose"
(file-name-sans-extension "big.hack/foo")
=> "big.hack/foo"
|
file-name-sans-versions to remove any
version/backup part. If period is non-nil, then the returned
value includes the period that delimits the extension, and if
filename has no extension, the value is "".
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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 most systems, this is simple: a directory name ends in a slash (or backslash), 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.
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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 and GNU/Linux, an absolute file name starts with a slash or a tilde (`~'), 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 `x:/', where x is the drive letter. 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
|
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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"
|
Note that expand-file-name does not expand environment
variables; only substitute-in-file-name does that.
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, filename has no relative equivalent based
on directory if they start with two different device names. In
this case, file-relative-name returns filename in absolute
form.
(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.
Aside from VMS, 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 "$HOME/foo")
=> "/xcssun/users/rms/foo"
|
After substitution, if a `~' or a `/' appears following a `/', everything before the following `/' is discarded:
(substitute-in-file-name "bar/~/foo")
=> "~/foo"
(substitute-in-file-name "/usr/local/$HOME/foo")
=> "/xcssun/users/rms/foo"
;; `/usr/local/' has been discarded.
|
On VMS, `$' substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.
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Some programs need to write temporary files. Here is the usual way to construct a name for such a file, starting in Emacs 21:
(make-temp-file name-of-application) |
The job of make-temp-file is to prevent two different users or
two different jobs from trying to use the exact same file name.
temporary-file-directory.
(make-temp-file "foo")
=> "/tmp/foo232J6v"
|
When 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 dir-flag is non-nil, make-temp-file creates
an empty directory instead of an empty file.
To prevent conflicts among different libraries running in the same
Emacs, each Lisp program that uses make-temp-file should have its
own prefix. The number added to the end of 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.
The default directory for temporary files is controlled by the
variable temporary-file-directory. This variable gives the user
a uniform way to specify the directory for all temporary files. Some
programs use small-temporary-file-directory instead, if that is
non-nil. To use it, you should expand the prefix against
the proper directory before calling make-temp-file.
In older Emacs versions where make-temp-file does not exist,
you should use make-temp-name instead:
(make-temp-name
(expand-file-name name-of-application
temporary-file-directory))
|
make-temp-file except
that it just constructs a name, and does not create a file. On MS-DOS,
the string prefix can be truncated to fit into the 8+3 file-name
limits.
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 TMPDIR, TMP and 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 make-temp-name to choose the temporary
file's name, 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 small-temporary-file-directory first if
that is non-nil.
If you want to write a temporary file which is likely to be small, you should compute the directory like this:
(make-temp-file
(expand-file-name prefix
(or small-temporary-file-directory
temporary-file-directory)))
|
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This section describes low-level subroutines for completing a file name. For other completion functions, see 20.5 Completion.
The argument partial-filename must be a file name containing no directory part and no slash (or backslash on some systems). The current buffer's default directory is prepended to directory, if directory is not absolute.
In the following example, suppose that `~rms/lewis' is the current default directory, and 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")
|
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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 `~/.abbrev_defs'; the completion
package stores completions in the 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
convert-standard-filename makes this easy to do.
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 convert-standard-filename instead of using it directly. Here
is an example from the completion package:
(defvar save-completions-file-name
(convert-standard-filename "~/.completions")
"*The file name to save completions to.")
|
On GNU and Unix systems, and on some other systems as well,
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 `.' to `_', converting a `_' in the middle of the name to `.' if there is no other `.', inserting a `.' after eight characters if there is none, and truncating to three characters after the `.'. (It makes other changes as well.) Thus, `.abbrev_defs' becomes `_abbrev.def', and `.completions' becomes `_complet.ion'.
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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.
If pattern is written as an absolute file name, the values are absolute also.
If 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
full is non-nil, they are absolute.
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 the directory
listing is expected to show the full contents of a directory. You
should specify t when file is a directory and switches do
not contain `-d'. (The `-d' option to ls says to
describe a directory itself as a file, rather than showing its
contents.)
On most systems, 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.
MS-DOS and MS-Windows systems usually lack the standard Unix program
ls, so this function emulates the standard Unix program ls
with Lisp code.
insert-directory. It is ignored on systems
which generate the listing with Lisp code.
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Most Emacs Lisp file-manipulation functions get errors when used on
files that are directories. For example, you cannot delete a directory
with delete-file. These special functions exist to create and
delete directories.
nil, that means to create
the parent directories first, if they don't already exist.
delete-file does not work for files that are directories; you
must use delete-directory for them. If the directory contains
any files, delete-directory signals an error.
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You can implement special handling for certain file names. This is called making those names magic. The principal use for this feature is in implementing remote file names (see section `Remote Files' in 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 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 primitive. (The first of these arguments is most often 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) |
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:
(expand-file-name filename dirname) |
then it checks for a handler for filename and then for a handler for dirname. In either case, the handler is called like this:
(funcall handler 'expand-file-name filename dirname) |
The handler then needs to figure out whether to handle filename or dirname.
Here are the operations that a magic file name handler gets to handle:
add-name-to-file, copy-file, delete-directory,
delete-file,
diff-latest-backup-file,
directory-file-name,
directory-files,
dired-call-process,
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-ownership-preserved-p,
file-readable-p, file-regular-p, file-symlink-p,
file-truename, file-writable-p,
find-backup-file-name,
get-file-buffer,
insert-directory,
insert-file-contents,
load, make-directory,
make-symbolic-link, rename-file, set-file-modes,
set-visited-file-modtime, shell-command,
unhandled-file-name-directory,
vc-registered,
verify-visited-file-modtime,
write-region.
Handlers for insert-file-contents typically need to clear the
buffer's modified flag, with (set-buffer-modified-p nil), if the
visit argument is non-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:
(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.
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The variable format-alist defines a list of 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.
Each format definition is a list of this form:
(name doc-string regexp from-fn to-fn modify mode-fn) |
Here is what the elements in a format definition mean:
A shell command is represented as a string; Emacs runs the command as a filter to perform the conversion.
If from-fn is a function, it is called with two arguments, begin and 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, from-fn should return the modified end position.
One responsibility of from-fn is to make sure that the beginning of the file no longer matches regexp. Otherwise it is likely to get called again.
If to-fn is a string, it is a shell command; Emacs runs the command as a filter to perform the conversion.
If to-fn is a function, it is called with two arguments, begin and end, which specify the part of the buffer it should convert. There are two ways it can do the conversion:
(position . string), where position is an
integer specifying the relative position in the text to be written, and
string is the annotation to add there. The list must be sorted in
order of position when to-fn returns it.
When 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.
t if the encoding function modifies the buffer, and
nil if it works by returning a list of annotations.
The function 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 find-file-noselect or the commands that use
it, performs conversion likewise (because it calls
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 buffer-file-format.
When write-region writes data into a file, it first calls the
encoding functions for the formats listed in buffer-file-format,
in the order of appearance in the list.
The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just
RET for format specifies nil.
nil, they specify which part of the file to read, as in
insert-file-contents (see section 25.3 Reading from Files).
The return value is like what insert-file-contents returns: a
list of the absolute file name and the length of the data inserted
(after conversion).
The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just
RET for format specifies nil.
buffer-file-format; however, it is used instead of
buffer-file-format for writing auto-save files. This variable is
always buffer-local in all buffers.
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