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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 @ref{Buffers}, and those related to backups and auto-saving are described in @ref{Backups and Auto-Saving}.
| 1.1 Visiting Files | Reading files into Emacs buffers for editing. | |
| 1.2 Saving Buffers | Writing changed buffers back into files. | |
| 1.3 Reading from Files | Reading files into buffers without visiting. | |
| 1.4 Writing to Files | Writing new files from parts of buffers. | |
| 1.5 File Locks | Locking and unlocking files, to prevent simultaneous editing by two people. | |
| 1.6 Information about Files | Testing existence, accessibility, size of files. | |
| 1.7 Contents of Directories | Getting a list of the files in a directory. | |
| 1.8 Creating and Deleting Directories | ||
| 1.9 Changing File Names and Attributes | Renaming files, changing protection, etc. | |
| 1.10 File Names | Decomposing and expanding file names. | |
| 1.11 Making Certain File Names “Magic” | Defining "magic" special handling for certain file names. |
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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 which 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.
| 1.1.1 Functions for Visiting Files | The usual interface functions for visiting. | |
| 1.1.2 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-’. @xref{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.
This function reads the file filename into a buffer and displays that buffer in the selected window so that the user can edit it.
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 @ref{Displaying Buffers}.)
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 reads a file into a buffer and returns the buffer. You may then make the buffer current or display it in a window if you wish, but this function does not do so.
If no buffer is currently visiting filename, then one is created
and the file is visited. If filename does not exist, the buffer
is left empty, and find-file-noselect displays the message
‘New file’ in the echo area.
If a buffer is already visiting filename, then the
find-file-noselect function uses that buffer rather than creating
a new one. However, it does verify 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.
The find-file-noselect function calls after-find-file
after the file is read in (see section Subroutines of Visiting). The
after-find-file function sets the buffer major mode, parses local
variables, warns the user if there exists an auto-save file more recent
than the file just visited, and finishes by running the functions in
find-file-hooks.
The find-file-noselect function returns the buffer that is
visiting the file filename.
(find-file-noselect "/etc/fstab")
⇒ #<buffer fstab>
This function reads the file filename into a buffer and selects it, killing the buffer current at the time the command is run. It is useful if you have visited the wrong file by mistake, so that you can get rid of the buffer that you did not want to create, at the same time as you visit the file you intended.
When this function is called interactively, it prompts for filename.
This function visits the file filename and displays its buffer in a window other than the selected window. It may use another existing window or split a window; see @ref{Displaying Buffers}.
When this function is called interactively, it prompts for filename.
This function visits the file named filename and selects its
buffer, just like find-file, but it marks the buffer as
read-only. @xref{Read Only Buffers}, for related functions and
variables.
When this function is called interactively, it prompts for filename.
This function views filename in View mode, returning to the previous buffer when done. View mode is a mode that allows you to skim rapidly through the file but does not let you modify it.
After loading the file, view-file runs the normal hook
view-hook using run-hooks. @xref{Hooks}.
When this function is called interactively, it prompts for filename.
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 could be a normal hook, but we think that renaming it would not be advisable.
The value of this variable is a list of functions to be called when
find-file or find-file-noselect is passed a nonexistent
filename. These functions are called as soon as the error is
detected. buffer-file-name is already set up. The functions are
called in the order given, until one of them returns non-nil.
This is not a normal hook because the values of the functions are used and they may not all be run.
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The find-file-noselect function uses the
create-file-buffer and after-find-file functions as
subroutines. Sometimes it is useful to call them directly.
This function creates a suitably named buffer for visiting filename, and returns it. The string filename (sans directory) is used unchanged if that name is free; otherwise, a string such as ‘<2>’ is appended to get an unused name. See also @ref{Creating Buffers}.
Please note: create-file-buffer does not
associate the new buffer with a file and does not make it the current
buffer.
(create-file-buffer "foo")
⇒ #<buffer foo>
(create-file-buffer "foo")
⇒ #<buffer foo<2>>
(create-file-buffer "foo")
⇒ #<buffer foo<3>>
This function is used by find-file-noselect.
It uses generate-new-buffer (@pxref{Creating Buffers}).
This function is called by find-file-noselect and by the
default revert function (@pxref{Reverting}). It sets the buffer major
mode, and parses local variables (@pxref{Auto Major Mode}).
If there was an error in opening the file, the calling function
should pass error a non-nil value. In that case,
after-find-file issues a warning: ‘(New File)’. Note that,
for serious errors, you would not even call after-find-file.
Only “file not found” errors get here with a non-nil
error.
If warn is non-nil, then this function issues a warning
if an auto-save file exists and is more recent than the visited file.
The last thing after-find-file does is call all the functions
in find-file-hooks.
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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 or if the buffer was previously
modified. 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 exiting argument, if non-nil, requests this
function to offer also to save certain other buffers that are not
visiting files. These are buffers that have a non-nil local
value of buffer-offer-save. (A user who says yes to saving one
of these is asked to specify a file name to use.) The
save-buffers-kill-emacs function passes a non-nil value
for this argument.
When this variable is non-nil in a buffer, Emacs offers to save
the buffer on exit even if the buffer is not visiting a file. The
variable is automatically local in all buffers. Normally, Mail mode
(used for editing outgoing mail) sets this to t.
This function writes the current buffer into file filename, makes the buffer visit that file, and marks it not modified. The buffer is renamed to correspond to filename unless that name is already in use.
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 basic-save-buffer does when it writes a
file in the usual way.
Here is an example showing how to add an element to
write-file-hooks but avoid adding it twice:
(or (memq 'my-write-file-hook write-file-hooks)
(setq write-file-hooks
(cons
'my-write-file-hook write-file-hooks)))
This works just like write-file-hooks, but it is intended
to be made local to particular buffers. It’s not a good idea to make
write-file-hooks local to a buffer—use this variable instead.
The variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. This is convenient for packages that read “file” contents in special ways, and set up hooks to save the data in a corresponding way.
This works just like write-file-hooks, but it is intended to be
used for hooks that pertain to the contents of the file, as opposed to
hooks that pertain to where the file came from.
This normal hook runs after a buffer has been saved in its visited 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.
(This feature worked differently in older Emacs versions.)
Some modes set this non-nil locally 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 Emacs silently puts 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 Emacs
asks the user whether to add a newline each time the case arises.
If the value of the variable is nil, then Emacs doesn’t add
newlines at all. nil is the default value, but a few major modes
set it to t in particular buffers.
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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.
If visit is non-nil, it also 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 should probably not use it yourself.
If you want to pass a file name to another process so that another
program can read the file, see the function file-local-copy in
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 (of the current buffer) delimited by start and end 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.
If append is non-nil, then the region is appended to the
existing file contents (if any).
If visit is t, then Emacs establishes an association
between the buffer and the file: the buffer is then visiting that file.
It also sets the last file modification time for the current buffer to
filename’s modtime, and marks the buffer as not modified. This
feature is used by write-file and you should probably 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.
Normally, write-region displays a message ‘Wrote file
filename’ in the echo area. If visit is neither t
nor nil nor a string, then this message is inhibited. This
feature is useful for programs that use files for internal purposes,
files which the user does not need to know about.
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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.
File locks do not work properly when multiple machines can share file systems, such as with NFS. Perhaps a better file locking system will be implemented in the future. When file locks do not work, it is possible for two users to make changes simultaneously, but Emacs can still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see @ref{Modification Time}.
This function returns nil if the file filename is not
locked by this Emacs process. It returns t if it is locked by
this Emacs, and it returns the name of the user who has locked it if it
is locked by someone else.
(file-locked-p "foo")
⇒ nil
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.
This function is called when the user tries to modify file, but it is locked by another user name other-user. The value it returns tells Emacs what to do next:
t tells Emacs to grab the lock on the file. Then
this user may edit the file and other-user loses the lock.
nil tells Emacs to ignore the lock and let this
user edit the file anyway.
file-locked error, in which
case the change to the buffer which 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.
The default definition of this function asks the user to choose what
to do. If you wish, you can replace the ask-user-about-lock
function with your own version that decides in another way. The code
for its usual definition is in ‘userlock.el’.
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The functions described in this section are similar in as much as they all operate on strings which are interpreted as file names. All have names that begin with the word ‘file’. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted.
Most of the file-oriented functions take a single argument,
filename, which must be a string. The file name is expanded using
expand-file-name, so ‘~’ is handled correctly, as are
relative file names (including ‘../’). Environment variable
substitutions, such as ‘$HOME’, are not recognized by these
functions. See section Functions that Expand Filenames.
| 1.6.1 Testing Accessibility | Is a given file readable? Writable? | |
| 1.6.2 Distinguishing Kinds of Files | Is it a directory? A symbolic link? | |
| 1.6.3 Truenames | Eliminating symbolic links from a file name. | |
| 1.6.4 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, 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. If the file
is a directory, execute permission means you can access files inside
the directory.
This function returns t if filename can be written or
created by you. It is writable if the file exists and you can write it.
It is creatable if the file does not exist, but the specified directory
does exist and you can write in that directory. file-writable-p
returns nil otherwise.
In the third example below, ‘foo’ is not writable because the parent directory does not exist, even though the user could create it.
(file-writable-p "~rms/foo")
⇒ t
(file-writable-p "/foo")
⇒ nil
(file-writable-p "~rms/no-such-dir/foo")
⇒ nil
This function returns t if you have permission to open existing
files in directory dirname; otherwise (and if there is no such
directory), it returns nil. The value of dirname may be
either a directory name or the file name of a directory.
Example: after the following,
(file-accessible-directory-p "/foo")
⇒ nil
we can deduce that any attempt to read a file in ‘/foo/’ will give an error.
This functions 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.
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.
In the following example, assume that the file ‘aug-19’ was written on the 19th, and ‘aug-20’ was written on the 20th. 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
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This section describes how to distinguish directories and symbolic links from ordinary files.
If 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 of
no file at all.
If 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
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The truename of a file is the name that you get by following symbolic links until none remain, then expanding to get rid of ‘.’ and ‘..’ as components. Strictly speaking, a file need not have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.
The function file-truename returns the true name of the file
filename. This is the name that you get by following symbolic
links until none remain. The argument must be an absolute file name.
@xref{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 @ref{Time of Day}.)
t if the file’s GID would change if file were
deleted and recreated; nil otherwise.
For example, here are the file attributes for ‘files.texi’:
(file-attributes "files.texi")
⇒ (nil
1
2235
75
(8489 20284)
(8489 20284)
(8489 20285)
14906
"-rw-rw-rw-"
nil
129500
-32252)
and here is how the result is interpreted:
nilis neither a directory nor a symbolic link.
1has only one name (the name ‘files.texi’ in the current default directory).
2235is owned by the user with UID 2235.
75is in the group with GID 75.
(8489 20284)was last accessed on Aug 19 00:09. Unfortunately, you cannot convert this number into a time string in Emacs.
(8489 20284)was last modified on Aug 19 00:09.
(8489 20285)last had its inode changed on Aug 19 00:09.
14906is 14906 characters long.
"-rw-rw-rw-"has a mode of read and write access for the owner, group, and world.
nilwould retain the same GID if it were recreated.
129500has an inode number of 129500.
-32252is on file system number -32252.
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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 value of switches 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 just the names relative to
the specified directory.
If match-regexp is non-nil, this function returns only
those file names that contain that regular expression—the other file
names are discarded from the list.
If nosort is non-nil, that inhibits sorting 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 inserts a directory listing for directory dir, formatted according to switches. It leaves point after the inserted text.
The argument dir may be either a directory name or a file
specification including wildcard characters. If wildcard is
non-nil, that means treat file as a file specification with
wildcards.
If full-directory-p is non-nil, that means file is a
directory and switches do not contain ‘d’, so that a full listing
is expected.
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.
This variable’s value is the program to run to generate a directory listing
for the function insert-directory.
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This function creates a directory named dirname.
This function deletes the directory named dirname. The function
delete-file does not work for files that are directories; you
must use delete-directory in that case.
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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 is signaled 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 -l fo* -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Then we evaluate the form (add-name-to-file "~/lewis/foo"
"~/lewis/foo2"). Again we list the files. This shows two names,
‘foo’ and ‘foo2’.
(add-name-to-file "~/lewis/foo1" "~/lewis/foo2")
⇒ nil
% ls -l fo* -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Finally, we evaluate the following:
(add-name-to-file "~/lewis/foo" "~/lewis/foo3" t)
and list the files again. Now there are three names for one file: ‘foo’, ‘foo2’, and ‘foo3’. The old contents of ‘foo3’ are lost.
(add-name-to-file "~/lewis/foo1" "~/lewis/foo3")
⇒ nil
% ls -l fo* -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
This function is meaningless on VMS, where multiple names for one file are not allowed.
See also file-nlinks in 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 functions gives the new
file the same last-modified time that the old one has. (This works on
only some operating systems.)
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
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. (In Unix, 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, filename and newname are read in the minibuffer, and ok-if-exists is set to the numeric prefix argument.
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 12 low 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. On Unix, the default protection is the bitwise complement of the “umask” value.
The argument mode must be an integer. Only the 9 low bits of mode are used.
Saving a modified version of an existing file does not count as creating the file; it does not change the file’s mode, and does not use the default file protection.
This function returns the current default protection value.
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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 the names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory.
On VMS, all these functions understand both VMS file name syntax and Unix syntax. This is so that all the standard Lisp libraries can specify file names in Unix syntax and work properly on VMS without change.
| 1.10.1 File Name Components | The directory part of a file name, and the rest. | |
| 1.10.2 Directory Names | A directory’s name as a directory is different from its name as a file. | |
| 1.10.3 Absolute and Relative File Names | Some file names are relative to a current directory. | |
| 1.10.4 Functions that Expand Filenames | Converting relative file names to absolute ones. | |
| 1.10.5 Generating Unique File Names | Generating names for temporary files. | |
| 1.10.6 File Name Completion | Finding the completions for a given file name. |
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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 in that directory. Therefore, a file name in Emacs is considered to have two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name.
On Unix, the directory part is everything up to and including the last slash; the nondirectory part is the rest. The rules in VMS syntax are complicated.
For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On Unix, only backup files have version numbers in their names; on VMS, every file has a version number, but most of the time the file name actually used in Emacs omits the version number. Version numbers are found mostly in directory lists.
This function returns the directory part of filename (or
nil if filename does not include a directory part). On
Unix, the function returns a string ending in a slash. On VMS, it
returns a string ending in one of the three characters ‘:’,
‘]’, or ‘>’.
(file-name-directory "lewis/foo") ; Unix example
⇒ "lewis/"
(file-name-directory "foo") ; Unix example
⇒ nil
(file-name-directory "[X]FOO.TMP") ; VMS example
⇒ "[X]"
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 without any file version numbers, backup version numbers, or trailing tildes.
(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"
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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 Unix, this is simple: a directory name ends in a slash, whereas the directory’s name as a file lacks that slash. On VMS, the relationship is more complicated.
The difference between a directory name and its name as a file is subtle but crucial. When an Emacs variable or function argument is described as being a directory name, a file name of a directory is not acceptable.
These two functions take a single argument, filename, which must
be a string. Environment variable substitutions such as ‘$HOME’,
and the symbols ‘~’, and ‘..’, are not expanded. Use
expand-file-name or substitute-in-file-name for that
(see section Functions that Expand Filenames).
This function returns a string representing filename in a form that the operating system will interpret as the name of a directory. In Unix, this means that a slash is appended to the string. 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 Unix, this means removing a final slash 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.
If you wish 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.
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"))
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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 an relative file name. On Unix, an absolute file name starts with a slash or a tilde (‘~’), and a relative one does not. The rules on VMS are complicated.
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 directory to start with if
filename is relative. (The value of directory should itself
be an absolute, expanded file name; it should not 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"
‘~/’ is expanded into the user’s home directory. A ‘/’ or ‘~’ following a ‘/’ is taken to be the start of an absolute file name that overrides what precedes it, so everything before that ‘/’ or ‘~’ is deleted. For example:
(expand-file-name
"/a1/gnu//usr/local/lib/emacs/etc/MACHINES")
⇒ "/usr/local/lib/emacs/etc/MACHINES"
(expand-file-name "/a1/gnu/~/foo")
⇒ "/xcssun/users/rms/foo"
In both cases, ‘/a1/gnu/’ is discarded because an absolute file name follows it.
Note that expand-file-name does not expand environment
variables; that is done only by substitute-in-file-name.
This function does the inverse of expansion—it tries to return a relative name which is equivalent to filename when interpreted relative to directory. (If such a relative name would be longer than the absolute name, it returns the absolute name instead.)
(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 is local in every buffer.
expand-file-name uses the default directory when its second
argument is nil.
On Unix systems, the value is always a string ending with a slash.
default-directory
⇒ "/user/lewis/manual/"
This function replaces environment variables names in filename with the values to which they are set by the operating system. 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 ‘$’ is a ‘{’, then the variable name is everything up to the matching ‘}’.
Here we assume that the environment variable HOME, which holds
the user’s home directory name, has the value ‘/xcssun/users/rms’.
(substitute-in-file-name "$HOME/foo")
⇒ "/xcssun/users/rms/foo"
If a ‘~’ or a ‘/’ appears following a ‘/’, after substitution, everything before the following ‘/’ is discarded:
(substitute-in-file-name "bar/~/foo")
⇒ "~/foo"
(substitute-in-file-name "/usr/local/$HOME/foo")
⇒ "/xcssun/users/rms/foo"
On VMS, ‘$’ substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.
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Some programs need to write temporary files. Here is the usual way to construct a name for such a file:
(make-temp-name (concat "/tmp/" name-of-application))
Here we use the directory ‘/tmp/’ because that is the standard
place on Unix for temporary files. The job of make-temp-name is
to prevent two different users or two different jobs from trying to use
the same name.
This function generates string that can be used as a unique name. The name starts with the prefix string, and ends with a number that is different in each Emacs job.
(make-temp-name "/tmp/foo")
⇒ "/tmp/foo021304"
To prevent conflicts among different application libraries run in the same Emacs, each application should have its own string. The number added to the end of the name distinguishes between the same application running in different Emacs jobs.
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This section describes low-level subroutines for completing a file name. For other completion functions, see @ref{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. The current buffer’s default directory is prepended to directory, if directory is not an absolute file name.
In the following example, suppose that the current default directory, ‘~rms/lewis’, has five files whose names begin with ‘f’: ‘foo’, ‘file~’, ‘file.c’, ‘file.c.~1~’, and ‘file.c.~2~’.
(file-name-all-completions "f" "")
⇒ ("foo" "file~" "file.c.~2~"
"file.c.~1~" "file.c")
(file-name-all-completions "fo" "")
⇒ ("foo")
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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You can implement special handling for certain file names. This is called making those names magic. You must supply a regular expression to define the class of names (all those which match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match.
The value of file-name-handler-alist is a list of handlers,
together with regular expressions that decide when to apply each
handler. Each element has this form:
(regexp . handler)
All the Emacs primitives for file access and file name transformation
check the given file name against file-name-handler-alist. If
the file name matches regexp, the primitives handle that file by
calling handler.
The first argument given to handler is the name of the primitive; the remaining arguments are the arguments that were passed to that operation. (The first of these arguments is typically the file name itself.) For example, if you do this:
(file-exists-p filename)
and filename has handler handler, then handler is called like this:
(funcall handler 'file-exists-p filename)
Here are the operations that you can handle for a magic file name:
add-name-to-file, copy-file, delete-directory,
delete-file, directory-file-name, directory-files,
dired-compress-file, dired-uncache,
expand-file-name, file-accessible-directory-p,
file-attributes, file-directory-p,
file-executable-p, file-exists-p, file-local-copy,
file-modes, file-name-all-completions,
file-name-as-directory, file-name-completion,
file-name-directory, file-name-nondirectory,
file-name-sans-versions, file-newer-than-file-p,
file-readable-p, file-symlink-p, file-writable-p,
insert-directory, insert-file-contents,
make-directory, make-symbolic-link, rename-file,
set-file-modes, set-visited-file-modtime,
unhandled-file-name-directory,
verify-visited-file-modtime, write-region.
The handler function must handle all of the above operations, and possibly others to be added in the future. Therefore, it should always reinvoke the ordinary Lisp primitive when it receives an operation it does not recognize. Here’s one way to do this:
(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 (file-name-handler-alist) (apply operation args)))))
This function returns the handler function for file name file, or
nil if there is none.
This function copies file filename to the local site, if it isn’t there 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. Otherwise, it asks the handler what to do.
This is used for running a subprocess; any subprocess must have a non-magic directory to serve as its current directory.
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