home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
User's Choice Windows CD
/
User's Choice Windows CD (CMS Software)(1993).iso
/
utility2
/
wine02bx.zip
/
INFO
/
ELISP.15
< prev
next >
Wrap
Text File
|
1993-03-28
|
48KB
|
1,136 lines
Info file elisp, produced by Makeinfo, -*- Text -*- from input file
elisp.texi.
This file documents GNU Emacs Lisp.
This is edition 1.03 of the GNU Emacs Lisp Reference Manual, for
Emacs Version 18.
Published by the Free Software Foundation, 675 Massachusetts
Avenue, Cambridge, MA 02139 USA
Copyright (C) 1990 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.
File: elisp, Node: Rename or Copy, Next: Numbered Backups, Prev: Making Backups, Up: Backup Files
Backup by Renaming or by Copying?
---------------------------------
There are two ways that Emacs can make a backup file:
* Emacs can rename the original file so that it becomes a backup
file, and then write the buffer being saved into a new file. In
this case, any other names (i.e., hard links) of the original
file will now refer to the backup file. The new file will be
owned by the user doing the editing, and its group will be the
default for the user or the directory.
* Emacs can copy the original file into a backup file, and then
overwrite the original file with new contents. In this case,
any other names (i.e., hard links) of the original file will
still refer to the current version of the file. The file's
owner and group will be unchanged.
The first method, renaming, is the default.
The variable `backup-by-copying', if non-`nil', says to use the
second method, which is to copy the original file and overwrite it
with the new buffer contents. The variable `file-precious-flag', if
non-`nil', also has this effect (as a sideline of its main
significance). *Note Saving Buffers::.
The variables `backup-by-copying-when-linked' and
`backup-by-copying-when-mismatch', if non-`nil', cause the second
method to be used in certain special cases. They have no effect on
the treatment of files that don't fall into the special cases.
* Variable: backup-by-copying
This variable controls whether to make backup files by copying.
If it is non-`nil', then Emacs always copies the current
contents of the file into the backup file before writing the
buffer to be saved to the file. (In many circumstances, this
has the same effect as `file-precious-flag'.)
* Variable: backup-by-copying-when-linked
This variable controls whether to make backups by copying for
files with multiple names (hard links). If it is non-`nil',
then Emacs will use copying to create backups for those files.
This variable is significant only if `backup-by-copying' is
`nil', since copying is always used when that variable is
non-`nil'.
* Variable: backup-by-copying-when-mismatch
This variable controls whether to make backups by copying when
renaming would cause either the owner or the group of the file
to change. If it is non-`nil' then Emacs will create backups by
copying in such cases.
The value has no effect when renaming would not result in
changing the owner or group of the file; that is, for files
which are owned by the user and whose group matches the default
for a new file created there by the user.
This variable is significant only if `backup-by-copying' is
`nil', since copying is always used when that variable is
non-`nil'.
File: elisp, Node: Numbered Backups, Next: Backup Names, Prev: Rename or Copy, Up: Backup Files
Making and Deleting Numbered Backup Files
-----------------------------------------
If a file's name is `foo', the names of its numbered backup
versions are `foo.~V~', for various integers V, like this: `foo.~1~',
`foo.~2~', `foo.~3~', ..., `foo.~259~', and so on.
* User Option: version-control
This variable controls whether to make a single non-numbered
backup file or multiple numbered backups.
`nil'
Make numbered backups if the visited file already has
numbered backups; otherwise, do not.
`never'
Do not make numbered backups.
ANYTHING ELSE
Do make numbered backups.
The use of numbered backups ultimately leads to a large number of
backup versions, which must then be deleted. Emacs can do this
automatically.
* User Option: kept-new-versions
The value of this variable is the number of oldest versions to
keep when a new numbered backup is made. The newly made backup
is included in the count. The default value is 2.
* User Option: kept-old-versions
The value of this variable is the number of oldest versions to
keep when a new numbered backup is made. The default value is 2.
* User Option: dired-kept-versions
This variable plays a role in Dired's `dired-clean-directory'
(`.') command like that played by `kept-old-versions' when a
backup file is made. The default value is 2.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 will be
kept as old versions and those numbered 5 and 7 will be kept as new
versions; backup version 3 will be deleted. The function
`find-backup-file-name' is responsible for determining which backup
versions to delete, but does not delete them itself.
* User Option: trim-versions-without-asking
If this variable is non-`nil', then excess backup versions are
deleted silently. Otherwise, the user is asked whether to
delete them.
File: elisp, Node: Backup Names, Prev: Numbered Backups, Up: Backup Files
Naming Backup Files
-------------------
The functions in this section are documented mainly because you
can customize the naming conventions for backup files by redefining
them.
* Function: backup-file-name-p FILENAME
This function returns a non-`nil' value if FILENAME is a
possible name for a backup file. A file with the name FILENAME
need not exist; the function just checks the name.
(backup-file-name-p "foo")
=> nil
(backup-file-name-p "foo~")
=> 3
The standard definition of this function is as follows:
(defun backup-file-name-p (file)
"Return non-nil if FILE is a backup file name (numeric or not)..."
(string-match "~$" file))
Thus, the function returns a non-`nil' value if the file name
ends with a `~'
This simple expression is placed in a separate function to make
it easy to redefine for customization.
* Function: make-backup-file-name FILENAME
This function returns a string which is the name to use for a
non-numbered backup file for file FILENAME. On Unix, this is
just FILENAME with a tilde appended.
The standard definition of this function is as follows:
(defun make-backup-file-name (file)
"Create the non-numeric backup file name for FILE..."
(concat file "~"))
You can change the backup file naming convention by redefining
this function. In the following example,
`make-backup-file-name' is redefined to prepend a `.' as well as
to append a tilde.
(defun make-backup-file-name (filename)
(concat "." filename "~"))
(make-backup-file-name "backups.texi")
=> ".backups.texi~"
If you do redefine `make-backup-file-name', be sure to redefine
`backup-file-name-p' and `find-backup-file-name' as well.
* Function: find-backup-file-name FILENAME
This function computes the file name for a new backup file for
FILENAME. It may also propose certain existing backup files for
deletion. `find-backup-file-name' returns a list whose CAR is
the name for the new backup file and whose CDR is a list of
backup files whose deletion is proposed.
Two variables called `kept-old-versions' and `kept-new-versions'
determine which old backup versions will be kept (by excluding
them from the list of backup files ripe for deletion). *Note
Numbered Backups::.
In this example, `~rms/foo.~5~' is the name to use for the new
backup file, and `~rms/foo.~3~' is an "excess" version that the
caller should consider deleting now.
(find-backup-file-name "~rms/foo")
=> ("~rms/foo.~5~" "~rms/foo.~3~")
File: elisp, Node: Auto-Saving, Next: Reverting, Prev: Backup Files, Up: Backups and Auto-Saving
Auto-Saving
===========
Emacs periodically saves all files that you are visiting; this is
called "auto-saving". Auto-saving prevents you from losing more than
a limited amount of work if the system crashes. By default,
auto-saves happen every 300 keystrokes. *Note Auto-Save:
(emacs)Auto-Save, for information on auto-save for users. Here we
describe the functions used to implement auto-saving and the
variables that control them.
* Variable: buffer-auto-save-file-name
This buffer-local variable is the name of the file used for
auto-saving the current buffer. It is `nil' if the buffer
should not be auto-saved.
buffer-auto-save-file-name
=> "/xcssun/users/rms/lewis/#files.texi#"
* Command: auto-save-mode ARG
When used interactively without an argument, this command is a
toggle switch: it turns on auto-saving of the current buffer if
it is off, and vice-versa. With an argument ARG, the command
turns auto-saving on if the value of ARG is `t', a nonempty
list, or a positive integer. Otherwise, it turns auto-saving off.
* Function: auto-save-file-name-p FILENAME
This function returns a non-`nil' value if FILENAME is a string
that could be the name of an auto-save file. It works based on
knowledge of the naming convention for auto-save files: a name
that begins and ends with hash marks (`#') is a possible
auto-save file name. The argument FILENAME should not contain a
directory part.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#files.texi#"
(auto-save-file-name-p "#files.texi#")
=> 0
(auto-save-file-name-p "files.texi")
=> nil
The standard definition of this function is as follows:
(defun auto-save-file-name-p (filename)
"Return non-nil if FILENAME can be yielded by..."
(string-match "^#.*#$" filename))
This function exists so that you can customize it if you wish to
change the naming convention for auto-save files. If you
redefine it, be sure to redefine `make-auto-save-file-name'
correspondingly.
* Function: make-auto-save-file-name
This function returns the file name to use for auto-saving the
current buffer. This is just the file name with hash marks
(`#') appended and prepended to it. This function does not look
at the variable `auto-save-visited-file-name'; that should be
checked before this function is called.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#backup.texi#"
The standard definition of this function is as follows:
(defun make-auto-save-file-name ()
"Return file name to use for auto-saves of current buffer..."
(if buffer-file-name
(concat (file-name-directory buffer-file-name)
"#"
(file-name-nondirectory buffer-file-name)
"#")
(expand-file-name (concat "#%" (buffer-name) "#"))))
This exists as a separate function so that you can redefine it
to customize the naming convention for auto-save files. Be sure
to change `auto-save-file-name-p' in a corresponding way.
* Variable: auto-save-visited-file-name
If this variable is non-`nil', Emacs will auto-save buffers in
the files they are visiting. That is, the auto-save is done in
the same file which you are editing. Normally, this variable is
`nil', so auto-save files have distinct names that are created
by `make-auto-save-file-name'.
When you change the value of this variable, the value does not
take effect until the next time auto-save mode is reenabled in
any given buffer. If auto-save mode is already enabled,
auto-saves continue to go in the same file name until
`auto-save-mode' is called again.
* Function: recent-auto-save-p
This function returns `t' if the current buffer has been
auto-saved since the last time it was read in or saved.
* Function: set-buffer-auto-saved
This function marks the current buffer as auto-saved. The
buffer will not be auto-saved again until the buffer text is
changed again. The function returns `nil'.
* User Option: auto-save-interval
The value of this variable is the number of characters that
Emacs reads from the keyboard between auto-saves. Each time
this many more characters are read, auto-saving is done for all
buffers in which it is enabled.
* User Option: auto-save-default
If this variable is non-`nil', buffers that are visiting files
have auto-saving enabled by default. Otherwise, they do not.
* Command: do-auto-save &optional NO-MESSAGE
This function auto-saves all buffers that need to be auto-saved.
This is all buffers for which auto-saving is enabled and that
have been changed since the last time they were auto-saved.
Normally, if any buffers are auto-saved, a message
`Auto-saving...' is displayed in the echo area while auto-saving
is going on. However, if NO-MESSAGE is non-`nil', the message
is inhibited.
* Function: delete-auto-save-file-if-necessary
This function deletes the auto-save file for the current buffer
if variable `delete-auto-save-files' is non-`nil'. It is called
every time a buffer is saved.
* Variable: delete-auto-save-files
This variable is used by the function
`delete-auto-save-file-if-necessary'. If it is non-`nil', Emacs
will delete auto-save files when a true save is done (in the
visited file). This saves on disk space and unclutters your
directory.
* Function: rename-auto-save-file
This function adjusts the current buffer's auto-save file name
if the visited file name has changed. It also renames an
existing auto-save file. If the visited file name has not
changed, this function does nothing.
File: elisp, Node: Reverting, Prev: Auto-Saving, Up: Backups and Auto-Saving
Reverting
=========
If you have made extensive changes to a file and then change your
mind about them, you can get rid of them by reading in the previous
version of the file with the `revert-buffer' command. *Note :
(emacs)Reverting.
* Command: revert-buffer &optional NO-AUTO-SAVE-OFFER-P NOCONFIRM
This command replaces the buffer text with the text of the
visited file on disk. This action undoes all changes since the
file was visited or saved.
When the value of the NO-AUTO-SAVE-OFFER-P argument is `nil',
and the latest auto-save file is more recent than the visited
file, `revert-buffer' asks the user whether to use that instead.
Otherwise, it always uses the latest backup file. This argument
is the numeric prefix argument when the function is called
interactively.
When the value of the NOCONFIRM argument is non-`nil',
`revert-buffer' does not ask for confirmation for the reversion
action. This means that the buffer contents are deleted and
replaced by the text from the file on the disk, with no further
opportunities for the user to prevent it.
Since reverting works by deleting the entire text of the buffer
and inserting the file contents, all the buffer's markers are
relocated to point at the beginning of the buffer. This is not
"correct", but then, there is no way to determine what would be
correct. It is not possible to determine, from the text before
and after, which characters after reversion correspond to which
characters before.
If the value of the `revert-buffer-function' variable is
non-`nil', it is called as a function with no arguments to do
the work.
* Variable: revert-buffer-function
The value of this variable is the function to use to revert this
buffer; but if the value of this variable is `nil', then the
`revert-buffer' function carries out its default action. Modes
such as Dired mode, in which the text being edited does not
consist of a file's contents but can be regenerated in some
other fashion, give this variable a buffer-local value that is a
function to regenerate the contents.
* Command: recover-file FILENAME
This function visits FILENAME, but gets the contents from its
last auto-save file. This is useful after the system has
crashed, to resume editing the same file without losing all the
work done in the previous session.
An error is signaled if there is no auto-save file for FILENAME,
or if FILENAME is newer than its auto-save file. If FILENAME
does not exist, but its auto-save file does, then the auto-save
file is read as usual. This last situation may occur if you
visited a nonexistent file and never actually saved it.
File: elisp, Node: Buffers, Next: Windows, Prev: Backups and Auto-Saving, Up: Top
Buffers
*******
A "buffer" is a Lisp object containing text to be edited. Buffers
are used to hold the contents of files that are being visited; there
may also be buffers which are not visiting files. While several
buffers may exist at one time, exactly one buffer is designated the
"current buffer" at any time. Most editing commands act on the
contents of the current buffer. Each buffer, including the current
buffer, may or may not be displayed in any windows.
* Menu:
* Buffer Basics:: What is a buffer?
* Buffer Names:: Accessing and changing buffer names.
* Buffer File Name:: The buffer file name indicates which file is visited.
* Buffer Modification:: A buffer is "modified" if it needs to be saved.
* Modification Time:: Determining whether the visited file was changed
"behind Emacs's back".
* Read Only Buffers:: Modifying text is not allowed in a read-only buffer.
* The Buffer List:: How to look at all the existing buffers.
* Creating Buffers:: Functions that create buffers.
* Killing Buffers:: Buffers exist until explicitly killed.
* Current Buffer:: Designating a buffer as current
so primitives will access its contents.
File: elisp, Node: Buffer Basics, Next: Buffer Names, Prev: Buffers, Up: Buffers
Buffer Basics
=============
A "buffer" is a Lisp object containing text to be edited. Buffers
are used to hold the contents of files that are being visited; there
may also be buffers which are not visiting files. While several
buffers may exist at one time, exactly one buffer is designated the
"current buffer" at any time. Most editing commands act on the
contents of the current buffer. Each buffer, including the current
buffer, may or may not be displayed in any windows.
Buffers in Emacs editing are objects which have distinct names and
hold text that can be edited. Buffers appear to Lisp programs as a
special data type. The contents of a buffer may be viewed as an
extendible string; insertions and deletions may occur in any part of
the buffer. *Note Text::.
A Lisp buffer object contains numerous pieces of information.
Some of this information is directly accessible to the programmer
through variables, while other information is only accessible through
special-purpose functions. For example, the width of a tab character
is directly accessible through a variable, while the value of point
is accessible only through a primitive function.
Buffer-specific information that is directly accessible is stored
in "buffer-local" variable bindings, which are variable values that
are effective only in a particular buffer. This feature allows each
buffer to override the values of certain variables. Most major modes
override variables such as `fill-column' or `comment-column' in this
way. For more information about buffer-local variables and functions
related to them, see *Note Buffer-Local Variables::.
For functions and variables related to visiting files in buffers,
see *Note Visiting Files:: and *Note Saving Buffers::. For functions
and variables related to the display of buffers in windows, see *Note
Buffers and Windows::.
* Function: bufferp OBJECT
This function returns `t' if OBJECT is a buffer, `nil' otherwise.
File: elisp, Node: Buffer Names, Next: Buffer File Name, Prev: Buffer Basics, Up: Buffers
Buffer Names
============
Each buffer has a unique name, which is a string. The buffer name
may be used in place of the buffer object in many functions that
operate on buffers. Buffers that are generally ephemeral and
uninteresting to the user have names starting with a space, which
prevents them from being listed by the `list-buffers' or
`buffer-menu' commands.
Many of the following functions accept either a buffer or a buffer
name (a string) as an argument. Any argument called BUFFER-OR-NAME
is of this sort, and an error is signaled if it is neither a string
nor a buffer. Any argument called BUFFER is required to be an actual
buffer object, not a name.
* Function: buffer-name &optional BUFFER
This function returns the name of BUFFER as a string. If BUFFER
is not supplied, it defaults to the current buffer.
If `buffer-name' returns `nil', it means that BUFFER has been
killed. *Note Killing Buffers::.
(buffer-name)
=> "buffers.texi"
(setq foo (get-buffer "temp"))
=> #<buffer temp>
(kill-buffer foo)
=> nil
(buffer-name foo)
=> nil
foo
=> #<killed buffer>
* Command: rename-buffer NEWNAME
This function renames the current buffer to NEWNAME. An error
is signaled if NEWNAME is not a string, or if there is already a
buffer with that name. The function returns `nil'.
One application of this command is to rename the `*shell*'
buffer to some other name, thus making it possible to create a
second shell buffer under the name `*shell*'.
* Function: get-buffer BUFFER-OR-NAME
This function returns the buffer specified by BUFFER-OR-NAME.
If BUFFER-OR-NAME is a string and there is no buffer with that
name, the value is `nil'. If BUFFER-OR-NAME is a buffer, it is
returned as given. (That is not very useful, so the argument is
usually a name.) For example:
(setq b (get-buffer "lewis"))
=> #<buffer lewis>
(get-buffer b)
=> #<buffer lewis>
(get-buffer "Frazzle-nots")
=> nil
File: elisp, Node: Buffer File Name, Next: Buffer Modification, Prev: Buffer Names, Up: Buffers
Buffer File Name
================
The "buffer file name" is the name of the file that is visited in
that buffer. When a buffer is not visiting a file, its buffer file
name is `nil'. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name
and the buffer name are distinct and can be set independently. *Note
Visiting Files::.
* Function: buffer-file-name &optional BUFFER
This function returns the absolute file name of the file that
BUFFER is visiting. If BUFFER is not visiting any file,
`buffer-file-name' returns `nil'. If BUFFER is not supplied, it
defaults to the current buffer.
(buffer-file-name (other-buffer))
=> "/usr/user/lewis/manual/files.texi"
* Variable: buffer-file-name
This buffer-local variable contains the name of the file being
visited in the current buffer, or `nil' if it is not visiting a
file.
buffer-file-name
=> "/usr/user/lewis/manual/buffers.texi"
It is risky to change this variable's value without doing
various other things. See the definition of
`set-visited-file-name' in `files.el'; some of the things done
there, such as changing the buffer name, are not necessary, but
others are essential to avoid confusing Emacs.
* Function: get-file-buffer FILENAME
This function returns the buffer visiting file FILENAME. If
there is no such buffer, it returns `nil'. The argument
FILENAME, which must be a string, is expanded (*note File Name
Expansion::.), then compared against the visited file names of
all live buffers.
(get-file-buffer "buffers.texi")
=> #<buffer buffers.texi>
In unusual circumstances, there can be more than one buffer
visiting the same file name. In such cases, this function
returns the first such buffer in the buffer list.
* Command: set-visited-file-name FILENAME
If FILENAME is a non-empty string, this function changes the
name of the file visited in current buffer to FILENAME. (If the
buffer had no visited file, this gives it one.) The *next time*
the buffer is saved it will go in the newly-specified file. The
buffer is always marked as modified, since it does not (as far
as Emacs knows) match the contents of FILENAME, even if it
matched the former visited file.
If FILENAME is `nil' or the empty string, that stands for "no
visited file". In this case, `set-visited-file-name' marks the
buffer as having no visited file.
When `set-visited-file-name' is called interactively, it prompts
for FILENAME in the minibuffer.
See also `clear-visited-file-modtime' and
`verify-visited-file-modtime' in *Note Buffer Modification::.
File: elisp, Node: Buffer Modification, Next: Modification Time, Prev: Buffer File Name, Up: Buffers
Buffer Modification
===================
Emacs keeps a flag called the "modified flag" for each buffer, to
record whether you have changed the text of the buffer. This flag is
set to `t' whenever you alter the contents of the buffer, and cleared
to `nil' when you save it. Thus, the flag shows whether there are
unsaved changes. The flag value is normally shown in the mode line
(*note Mode Line Variables::.), and controls saving (*note Saving
Buffers::.) and auto-saving (*note Auto-Saving::.).
Some Lisp programs set the flag explicitly. For example, the Lisp
function `set-visited-file-name' sets the flag to `t', because the
text does not match the newly-visited file, even if it is unchanged
from the file formerly visited.
The functions that modify the contents of buffers are described in
*Note Text::.
* Function: buffer-modified-p &optional BUFFER
This function returns `t' if the buffer BUFFER has been modified
since it was last read in from a file or saved, or `nil'
otherwise. If BUFFER is not supplied, the current buffer is
tested.
* Function: set-buffer-modified-p FLAG
This function marks the current buffer as modified if FLAG is
non-`nil', or as unmodified if the flag is `nil'.
Another effect of calling this function is to cause
unconditional redisplay of the mode line for the current buffer.
In fact, the standard way to force redisplay of the mode line is
as follows:
(set-buffer-modified-p (buffer-modified-p))
* Command: not-modified
This command marks the current buffer as unmodified, and not
needing to be saved. Don't use this function in programs, since
it prints a message; use `set-buffer-modified-p' (above) instead.
File: elisp, Node: Modification Time, Next: Read Only Buffers, Prev: Buffer Modification, Up: Buffers
Comparison of Modification Time
===============================
Suppose that you visit a file and make changes in its buffer, and
meanwhile the file itself is changed on disk. At this point, saving
the buffer would overwrite the changes in the file. Occasionally
this may be what you want, but usually it would lose valuable
information. Emacs therefore checks the file's modification time
using the functions described below before saving the file.
* Function: verify-visited-file-modtime BUFFER
This function compares Emacs's record of the modification time
for the file that the buffer is visiting against the actual
modification time of the file as recorded by the operating
system. The two will be the same unless some other process has
written the file since Emacs visited or saved it.
The function returns `t' if the last actual modification time
and Emacs's recorded modification time are the same, `nil'
otherwise.
* Function: clear-visited-file-modtime
This function clears out the record of the last modification
time of the file being visited by the current buffer. As a
result, the next attempt to save this buffer will not complain
of a discrepancy in file modification times.
This function is called in `set-visited-file-name' and other
exceptional places where the usual test to avoid overwriting a
changed file should not be done.
* Function: ask-user-about-supersession-threat FN
This function is used to ask a user how to proceed after an
attempt to modify an obsolete buffer. An "obsolete buffer" is
an unmodified buffer for which the associated file on disk is
newer than the last save-time of the buffer. This means some
other program has probably altered the file.
This function is called automatically by Emacs on the proper
occasions. It exists so you can customize Emacs by redefining it.
See the file `userlock.el' for the standard definition.
Depending on the user's answer, the function may return
normally, in which case the modification of the buffer proceeds,
or it may signal a `file-supersession' error with data `(FN)',
in which case the proposed buffer modification is not allowed.
See also the file locking mechanism in *Note File Locks::.
File: elisp, Node: Read Only Buffers, Next: The Buffer List, Prev: Modification Time, Up: Buffers
Read-Only Buffers
=================
A buffer may be designated as "read-only". This means that the
buffer's contents may not be modified, although you may change your
view of the contents by scrolling, narrowing, or widening, etc.
Read-only buffers are used in two kinds of situations:
* A buffer visiting a file is made read-only if the file is
write-protected.
Here, the purpose is to show the user that editing the buffer
with the aim of saving it in the file may be futile or
undesirable. The user who wants to change the buffer text
despite this can do so after clearing the read-only flag with
the function `toggle-read-only'.
* Modes such as Dired and Rmail make buffers read-only when
altering the contents with the usual editing commands is
probably a mistake.
The special commands of the mode in question bind
`buffer-read-only' to `nil' (with `let') around the places where
they change the text.
* Variable: buffer-read-only
This buffer-local variable specifies whether the buffer is
read-only. The buffer is read-only if this variable is non-`nil'.
* Command: toggle-read-only
This command changes whether the current buffer is read-only.
It is intended for interactive use; don't use it in programs.
At any given point in a program, you should know whether you
want the read-only flag on or off; so you can set
`buffer-read-only' explicitly to the proper value, `t' or `nil'.
* Function: barf-if-buffer-read-only
This function signals a `buffer-read-only' error if the current
buffer is read-only. *Note Interactive Call::, for another way
to signal an error if the current buffer is read-only.
File: elisp, Node: The Buffer List, Next: Creating Buffers, Prev: Read Only Buffers, Up: Buffers
The Buffer List
===============
The "buffer list" is a list of all buffers that have not been
killed. The order of the buffers in the list is based primarily on
how recently each buffer has been displayed in the selected window.
Several functions, notably `other-buffer', make use of this ordering.
* Function: buffer-list
This function returns a list of all buffers, including those
whose names begin with a space. The elements are actual
buffers, not their names.
(buffer-list)
=> (#<buffer buffers.texi> #<buffer *Minibuf-1*>
#<buffer buffer.c> #<buffer *Help*> #<buffer TAGS>)
;; Note that the name of the minibuffer begins with a space!
(mapcar (function buffer-name) (buffer-list))
=> ("buffers.texi" " *Minibuf-1*" "buffer.c" "*Help*" "TAGS")
This list is a copy of a list used inside Emacs; modifying it
has no effect on the buffers.
* Function: other-buffer &optional BUFFER-OR-NAME
This function returns the first buffer in the buffer list other
than BUFFER-OR-NAME. Usually this is the buffer most recently
shown in the selected window, aside from BUFFER-OR-NAME.
Buffers are moved to the front of the list when they are
selected and to the end when they are buried. Buffers whose
names start with a space are not even considered.
If BUFFER-OR-NAME is not supplied (or if it is not a buffer),
then `other-buffer' returns the first buffer on the buffer list
that is not visible in any window.
If no suitable buffer exists, the buffer `*scratch*' is returned
(and created, if necessary).
* Command: list-buffers &optional FILES-ONLY
This function displays a listing of the names of existing
buffers. It clears the buffer `*Buffer List*', then inserts the
listing into that buffer and displays it in a window.
`list-buffers' is intended for interactive use, and is described
fully in ``The GNU Emacs Manual''. It returns `nil'.
* Command: bury-buffer &optional BUFFER-OR-NAME
This function puts BUFFER-OR-NAME at the end of the buffer list
without changing the order of any of the other buffers on the
list. This buffer therefore becomes the least desirable
candidate for `other-buffer' to return, and appears last in the
list displayed by `list-buffers'.
If BUFFER-OR-NAME is the current buffer, then it is replaced in
the selected window by the buffer chosen using `other-buffer'.
If the buffer is displayed in a window other than the selected
one, it remains there.
If BUFFER-OR-NAME is not supplied, it defaults to the current
buffer. This is what happens in an interactive call.
File: elisp, Node: Creating Buffers, Next: Killing Buffers, Prev: The Buffer List, Up: Buffers
Creating Buffers
================
This section describes the two primitives for creating buffers.
`get-buffer-create' creates a buffer if it finds no existing buffer;
`generate-new-buffer' always creates a new buffer, and gives it a
unique name.
Two other functions to create buffers are
`with-output-to-temp-buffer' (*note Temporary Displays::.) and
`create-file-buffer' (*note Visiting Files::.).
* Function: get-buffer-create NAME
This function returns a buffer named NAME. If such a buffer
already exists, it is returned. If such a buffer does not
exist, one is created and returned. The buffer does not become
the current buffer--this function does not change which buffer
is current.
An error is signaled if NAME is not a string.
(get-buffer-create "foo")
=> #<buffer foo>
The major mode for the new buffer is chosen according to the
value of `default-major-mode'. *Note Auto Major Mode::.
* Function: generate-new-buffer NAME
This function returns a newly created, empty buffer. If there
is no buffer named NAME, then that is the name of the new
buffer. If there is a buffer with that name, then suffixes of
the form `<N>' are added to NAME, where N stands for successive
integers starting with 2. New suffixes are tried until an
unused name is found.
An error is signaled if NAME is not a string.
(generate-new-buffer "bar")
=> #<buffer bar>
(generate-new-buffer "bar")
=> #<buffer bar<2>>
(generate-new-buffer "bar")
=> #<buffer bar<3>>
The major mode for the new buffer is chosen according to the
value of `default-major-mode'. *Note Auto Major Mode::.
File: elisp, Node: Killing Buffers, Next: Current Buffer, Prev: Creating Buffers, Up: Buffers
Killing Buffers
===============
"Killing a buffer" makes its name unknown to Emacs and makes its
space available for other use.
The buffer object for the buffer which has been killed remains in
existence as long as anything refers to it, but it is specially
marked so that you cannot make it current or display it. Killed
buffers retain their identity, however; two distinct buffers, when
killed, remain distinct according to `eq'.
The `buffer-name' of a killed buffer is `nil'. You can use this
feature to test whether a buffer has been killed:
(defun killed-buffer-p (buffer)
"Return t if BUFFER is killed."
(not (buffer-name buffer)))
* Command: kill-buffer BUFFER-OR-NAME
This function kills the buffer BUFFER-OR-NAME, freeing all its
memory for use as space for other buffers. (In Emacs version
18, the memory is not returned to the operating system.) It
returns `nil'.
Any processes that have this buffer as the `process-buffer' are
sent the `SIGHUP' signal, which normally causes them to terminate.
(The usual meaning of `SIGHUP' is that a dialup line has been
disconnected.) *Note Deleting Processes::.
If the buffer is visiting a file when `kill-buffer' is called
and the buffer has not been saved since it was last modified,
the user is asked to confirm before the buffer is killed. This
is done even if `kill-buffer' is not called interactively. To
prevent the request for confirmation, clear the modified flag
before calling `kill-buffer'. *Note Buffer Modification::.
(kill-buffer "foo.unchanged")
=> nil
(kill-buffer "foo.changed")
---------- Buffer: Minibuffer ----------
Buffer foo.changed modified; kill anyway? (yes or no) `yes'
---------- Buffer: Minibuffer ----------
=> nil
File: elisp, Node: Current Buffer, Prev: Killing Buffers, Up: Buffers
The Current Buffer
==================
There are in general many buffers in an Emacs session. At any
time, one of them is designated as the "current buffer". This is the
buffer in which most editing takes place, because most of the
primitives for examining or changing text in a buffer operate
implicitly on the current buffer (*note Text::.). Normally the
buffer that is displayed on the screen in the selected window is the
current buffer, but this is not always so: a Lisp program can
designate any buffer as current temporarily in order to operate on
its contents, without changing what is displayed on the screen.
The way to designate a current buffer in a Lisp program is by
calling `set-buffer'. The specified buffer remains current until a
new one is designated.
When an editing command returns to the editor command loop, the
command loop designates the buffer displayed in the selected window
as current, to prevent confusion: the buffer that the cursor is in,
when Emacs reads a command, is the one to which the command will apply.
(*Note Command Loop::.) Therefore, `set-buffer' is not usable for
switching visibly to a different buffer so that the user can edit it.
For this, you must use the functions described in *Note Displaying
Buffers::.
However, Lisp functions that change to a different current buffer
should not rely on the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other
programs as well as from the command loop. It is convenient for the
caller if the subroutine does not change which buffer is current
(unless, of course, that is the subroutine's purpose). Therefore,
you should normally use `set-buffer' within a `save-excursion' that
will restore the current buffer when your program is done (*note
Excursions::.). Here is an example, the code for the command
`append-to-buffer' (with the documentation string abridged):
(defun append-to-buffer (buffer start end)
"Append to specified buffer the text of the region..."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(save-excursion
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
In this function, a local variable is bound to the current buffer,
and then `save-excursion' records the values of point, the mark, and
the original buffer. Next, `set-buffer' makes another buffer current.
Finally, `insert-buffer-substring' copies the string from the
original current buffer to the new current buffer.
If the buffer appended to happens to be displayed in some window,
then the next redisplay will show how its text has changed.
Otherwise, you will not see the change immediately on the screen.
The buffer becomes current temporarily during the execution of the
command, but this does not cause it to be displayed.
* Function: current-buffer
This function returns the current buffer.
(current-buffer)
=> #<buffer buffers.texi>
* Function: set-buffer BUFFER-OR-NAME
This function makes BUFFER-OR-NAME the current buffer. However,
it does not display the buffer in the currently selected window
or in any other window. This means that the user cannot
necessarily see the buffer, but Lisp programs can in any case
work on it.
This function returns the buffer identified by BUFFER-OR-NAME.
An error is signaled if BUFFER-OR-NAME does not identify an
existing buffer.
File: elisp, Node: Windows, Next: Positions, Prev: Buffers, Up: Top
Windows
*******
This chapter describes most of the functions and variables related
to Emacs windows. See *Note Emacs Display::, for information on how
text is displayed in windows.
* Menu:
* Basic Windows:: Basic information on using windows.
* Splitting Windows:: Splitting one window into two windows.
* Deleting Windows:: Deleting a window gives its space to other windows.
* Selecting Windows:: The selected window is the one that you edit in.
* Cyclic Window Ordering:: Moving around the existing windows.
* Buffers and Windows:: Each window displays the contents of a buffer.
* Displaying Buffers:: Higher-lever functions for displaying a buffer
and choosing a window for it.
* Window Point:: Each window has its own location of point.
* Window Start:: The display-start position controls which text
is on-screen in the window.
* Vertical Scrolling:: Moving text up and down in the window.
* Horizontal Scrolling:: Moving text sideways on the window.
* Size of Window:: Accessing the size of a window.
* Resizing Windows:: Changing the size of a window.
* Window Configurations:: Saving and restoring the state of the screen.
File: elisp, Node: Basic Windows, Next: Splitting Windows, Prev: Windows, Up: Windows
Basic Concepts of Emacs Windows
===============================
A "window" is the physical area of the screen in which a buffer is
displayed. The term is also used to refer to a Lisp object which
represents that screen area in Emacs Lisp. It should be clear from
the context which is meant.
There is always at least one window displayed on the screen, and
there is exactly one window that we call the "selected window". The
cursor is in the selected window. The selected window's buffer is
usually the current buffer (except when `set-buffer' has been used.)
*Note Current Buffer::.
For all intents, a window only exists while it is displayed on the
terminal. Once removed from the display, the window is effectively
deleted and should not be used, *even though there may still be
references to it* from other Lisp objects. (*Note Deleting Windows::.)
Each window has the following attributes:
* window height
* window width
* window edges with respect to the screen
* the buffer it displays
* position within the buffer at the upper left of the window
* the amount of horizontal scrolling, in columns
* point
* the mark
* how recently the window was selected
Applications use multiple windows for a variety of reasons, but
most often to give different views of the same information. In
Rmail, for example, you can move through a summary buffer in one
window while the other window shows messages one at a time as they
are reached.
Use of the word "window" to refer to a view of a buffer was
established long ago in Emacs. The metaphor was inspired by how you
look out a house window--at part (or sometimes all) of an overall view.
You see part (or sometimes all) of a buffer through an Emacs window.
In Emacs, each window may look on a different view, like different
windows of a house.
The term "window" as used in this manual means something different
from the term as used in a window system like X Windows. In this
manual, the term "window" refers to the nonoverlapping subdivisions
of the Emacs display. If Emacs is displaying on a window system, the
Emacs display may itself be one X window among many on the screen.
But Emacs version 18 knows nothing of this.
For those familiar with windowing systems, Emacs's windows are
rectangles tiled onto the rectangle of the screen, and every portion
of the screen is part of some window, except (sometimes) the
minibuffer area. This limitation helps avoid wasting the
historically scarce resource of screen space. It also works well
with character-only terminals. Because of the way in which Emacs
creates new windows and resizes them, you can't create every
conceivable tiling on an Emacs screen. *Note Splitting Windows::.
Also, see *Note Size of Window::.
*Note Emacs Display::, for information on how the contents of the
window's buffer are displayed in the window.
* Function: windowp OBJECT
This function returns `t' if OBJECT is a window.