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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.