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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 Buffers, and those related to backups and auto-saving are described in 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 Functions that Expand Filenames.
When file I/O functions signal Lisp errors, they usually use the
condition file-error
(see section 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 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 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 Reading from Files.
This command selects a buffer visiting the file filename, using an existing buffer if there is one, and otherwise creating a new buffer and reading the file into it. It also returns that buffer.
The body of the find-file
function is very simple and looks
like this:
(switch-to-buffer (find-file-noselect filename)) |
(See switch-to-buffer
in 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.
This function is the guts of all the file-visiting functions. It finds or creates a buffer visiting the file filename, and returns it. It uses an existing buffer if there is one, and otherwise creates a new buffer and reads the file into it. You may make the buffer current or display it in a window if you wish, but this function does not do so.
If 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 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 Coding Systems) and format conversion (see section 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> |
This command selects a buffer visiting the file filename, but does so in a window other than the selected window. It may use another existing window or split a window; see Displaying Buffers in Windows.
When this command is called interactively, it prompts for filename.
This command selects a buffer visiting the file filename, like
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.
This command visits filename using View mode, returning to the
previous buffer when you exit View mode. View mode is a minor mode that
provides commands to skim rapidly through the file, but does not let you
modify the text. Entering View mode runs the normal hook
view-mode-hook
. See section Hooks.
When view-file
is called interactively, it prompts for
filename.
If this variable is non-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.
The value of this variable is a list of functions to be called after a file is visited. The file’s local-variables specification (if any) will have been processed before the hooks are run. The buffer visiting the file is current when the hook functions are run.
This variable works just like a normal hook, but we think that renaming it would not be advisable. See section Hooks.
The value of this variable is a list of functions to be called when
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.
This function creates a suitably named buffer for visiting filename, and returns it. It uses filename (sans directory) as the name if that name is free; otherwise, it appends a string such as ‘<2>’ to get an unused name. See also Creating Buffers.
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 Creating Buffers).
This function sets the buffer major mode, and parses local variables
(see section How Emacs Chooses a Major Mode). It is called by 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.
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.
This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing.
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.
This command saves some modified file-visiting buffers. Normally it
asks the user about each buffer. But if save-silently-p is
non-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.
This function writes the current buffer into file filename, makes
the buffer visit that file, and marks it not modified. Then it renames
the buffer based on filename, appending a string like ‘<2>’
if necessary to make a unique buffer name. It does most of this work by
calling set-visited-file-name
(see section 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 File Format Conversion), and may save text properties in “annotations” (see section Saving Text Properties in Files).
The value of this variable is a list of functions to be called before
writing out a buffer to its visited file. If one of them returns
non-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 Coding Systems in Lisp), perform the encoding
(see section Explicit Encoding and Decoding), and set last-coding-system-used
to
the coding system that was used (see section 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 Hooks.
This works just like 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.
This works just like 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.
This normal hook runs after a buffer has been saved in its visited file. One use of this hook is in Fast Lock mode; it uses this hook to save the highlighting information in a cache file.
If this variable is non-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 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.
This variable determines whether files may be written out that do
not end with a newline. If the value of the variable is
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 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.
This function inserts the contents of file filename into the current buffer after point. It returns a list of the absolute file name and the length of the data inserted. An error is signaled if filename is not the name of a file that can be read.
The function insert-file-contents
checks the file contents
against the defined file formats, and converts the file contents if
appropriate. See section File Format Conversion. It also calls the functions in
the list after-insert-file-functions
; see Saving Text Properties in Files. Normally, one of the functions in the
after-insert-file-functions
list determines the coding system
(see section 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
.
This function works like insert-file-contents
except that it does
not do format decoding (see section File Format Conversion), does not do
character code conversion (see section 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
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.
This function appends the contents of the region delimited by
start and end in the current buffer to the end of file
filename. If that file does not exist, it is created. This
function returns nil
.
An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.
This function writes the region delimited by start and end in the current buffer into the file specified by filename.
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 File Format Conversion. It also calls the functions in the list
write-region-annotate-functions
; see 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.
The 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 Nonlocal Exits).
See also with-temp-buffer
in 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 Comparison of Modification Time.
This function returns 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 |
This function locks the file filename, if the current buffer is modified. The argument filename defaults to the current buffer’s visited file. Nothing is done if the current buffer is not visiting a file, or is not modified.
This function unlocks the file being visited in the current buffer, if the buffer is modified. If the buffer is not modified, then the file should not be locked, so this function does nothing. It also does nothing if the current buffer is not visiting a file.
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
.
This function is called when the user tries to modify file, but it is locked by another user named other-user. The default definition of this function asks the user to say what to do. The value this function returns determines what Emacs does next:
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.
This function returns 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
.
This function returns 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 |
This function returns 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.
This function returns 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 |
This function returns 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.
This function opens file filename for reading, then closes it and
returns nil
. However, if the open fails, it signals an error
using string as the error message text.
This function returns t
if deleting the file filename and
then creating it anew would keep the file’s owner unchanged.
This function returns 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.
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This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files.
If the file filename is a symbolic link, the 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" |
This function returns 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 |
This function returns 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.
The function file-truename
returns the truename of the file
filename. The argument must be an absolute file name.
This function follows symbolic links, starting with filename, until it finds a file name which is not the name of a symbolic link. Then it returns that 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 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.
This function returns the mode bits of filename, as an integer. The mode bits are also called the file permissions, and they specify access control in the usual Unix fashion. If the low-order bit is 1, then the file is executable by all users, if the second-lowest-order bit is 1, then the file is writable by all users, etc.
The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the 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 |
This functions returns the number of names (i.e., hard links) that
file filename has. If the file does not exist, then this function
returns 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 |
This function returns a list of attributes of file filename. If
the specified file cannot be opened, it returns 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 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
is neither a directory nor a symbolic link.
1
has only one name (the name ‘files.texi’ in the current default directory).
2235
is owned by the user with UID 2235.
75
is in the group with GID 75.
(8489 20284)
was last accessed on Aug 19 00:09.
(8489 20284)
was last modified on Aug 19 00:09.
(8489 20285)
last had its inode changed on Aug 19 00:09.
14906
is 14906 bytes long. (It may not contain 14906 characters, though, if some of the bytes belong to multibyte sequences.)
"-rw-rw-rw-"
has a mode of read and write access for the owner, group, and world.
nil
would retain the same GID if it were recreated.
129500
has an inode number of 129500.
-32252
is on file system number -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
.
This function gives the file named oldname the additional name newname. This means that newname becomes a new “hard link” to oldname.
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 Other Information about Files.
This command renames the file filename as newname.
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.
This command copies the file oldname to newname. An error is signaled if oldname does not exist.
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.
This command deletes the file filename, like the shell command ‘rm filename’. If the file has multiple names, it continues to exist under the other names.
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 Creating and Deleting Directories.
This command makes a symbolic link to filename, named newname. This is like the shell command ‘ln -s filename newname’.
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.
This function defines the logical name name to have the value string. It is available only on VMS.
This function sets mode bits of filename to mode (which must be an integer). Only the low 12 bits of mode are used.
This function sets the default file protection for new files created by
Emacs and its subprocesses. Every file created with Emacs initially has
this protection, or a subset of it (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.
This function returns the current default protection value.
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.
This function returns the directory part of filename (or
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]"
|
This function returns the nondirectory part of filename.
(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"
|
This function returns filename with any file version numbers, backup version numbers, or trailing tildes discarded.
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"
|
This function returns filename minus its “extension,” if any. The extension, in a file name, is the part that starts with the last ‘.’ in the last name component. For example,
(file-name-sans-extension "foo.lose.c") ⇒ "foo.lose" (file-name-sans-extension "big.hack/foo") ⇒ "big.hack/foo" |
This function returns filename’s final “extension,” if any,
after applying 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 ‘..’.
This function returns a string representing filename in a form that the operating system will interpret as the name of a directory. On most systems, this means appending a slash to the string (if it does not already end in one). On VMS, the function converts a string of the form ‘[X]Y.DIR.1’ to the form ‘[X.Y]’.
(file-name-as-directory "~rms/lewis") ⇒ "~rms/lewis/" |
This function returns a string representing dirname in a form that the operating system will interpret as the name of a file. On most systems, this means removing the final slash (or backslash) from the string. On VMS, the function converts a string of the form ‘[X.Y]’ to ‘[X]Y.DIR.1’.
(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.
The variable 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:
This function applies abbreviations from 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.
This function returns 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/../’.
This function converts filename to an absolute file name. If
directory is supplied, it is the default directory to start with
if filename is relative. (The value of directory should
itself be an absolute directory name; it may start with ‘~’.)
Otherwise, the current buffer’s value of 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.
This function does the inverse of expansion—it tries to return a
relative name that is equivalent to filename when interpreted
relative to directory. If directory is omitted or
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" |
The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with ‘~’. This variable is buffer-local in every buffer.
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/" |
This function replaces environment variables references in filename with the environment variable values. Following standard Unix shell syntax, ‘$’ is the prefix to substitute an environment variable value.
The environment variable name is the series of alphanumeric characters (including underscores) that follow the ‘$’. 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.
This function creates a temporary file and returns its name.
The name starts with prefix; it also contains a number that is
different in each Emacs job. If prefix is a relative file name,
it is expanded against 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)) |
This function generates a string that can be used as a unique file name.
The name starts with string, and contains a number that is
different in each Emacs job. It is like 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.
This variable specifies the directory name for creating temporary files.
Its value should be a directory name (see section Directory Names), but it
is good for Lisp programs to cope if the value is a directory’s file
name instead. Using the value as the second argument to
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
.
This variable (new in Emacs 21) specifies the directory name for creating certain temporary files, which are likely to be small.
If you want to write a temporary file which is likely to be small, you should compute the directory like this:
(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 Completion.
This function returns a list of all possible completions for a file whose name starts with partial-filename in directory directory. The order of the completions is the order of the files in the directory, which is unpredictable and conveys no useful information.
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") |
This function completes the file name filename in directory directory. It returns the longest prefix common to all file names in directory directory that start with filename.
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.
This function alters the file name filename to fit the conventions of the operating system in use, and returns the result as a new string.
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.
This function returns a list of the names of the files in the directory directory. By default, the list is in alphabetical order.
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.
This function returns a list of all versions of the file named file in directory dirname.
This function expands the wildcard pattern pattern, returning a list of file names that match it.
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.
This function inserts (in the current buffer) a directory listing for
directory file, formatted with 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.
This variable’s value is the program to run to generate a directory listing
for the function 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.
This function creates a directory named dirname.
If parents is non-nil
, that means to create
the parent directories first, if they don’t already exist.
This function deletes the directory named dirname. The function
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 (emacs)Remote Files 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.
This variable holds a list of handlers whose use is presently inhibited for a certain operation.
The operation for which certain handlers are presently inhibited.
This function returns the handler function for file name file, or
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
.
This function copies file filename to an ordinary non-magic file, if it isn’t one already.
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 function returns the name of a directory that is not magic. It uses the directory part of filename if that is not magic. For a magic file name, it invokes the file name handler, which therefore decides what value to return.
This is useful for running a subprocess; every subprocess must have a non-magic directory to serve as its current directory, and this function is a good way to come up with one.
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This document was generated by Yasutaka SHINDOH on April 18, 2010 using texi2html 1.82.