@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001, 2002, @c 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. @c See the file elisp.texi for copying conditions. @setfilename ../info/buffers @node Buffers, Windows, Backups and Auto-Saving, Top @chapter Buffers @cindex buffer A @dfn{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 that are not visiting files. While several buffers may exist at one time, only one buffer is designated the @dfn{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? * Current Buffer:: Designating a buffer as current so that primitives will access its contents. * Buffer Names:: Accessing and changing buffer names. * Buffer File Name:: The buffer file name indicates which file is visited. * Buffer Modification:: A buffer is @dfn{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. * Indirect Buffers:: An indirect buffer shares text with some other buffer. * Buffer Gap:: The gap in the buffer. @end menu @node Buffer Basics @comment node-name, next, previous, up @section Buffer Basics @ifnottex A @dfn{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 that are not visiting files. Although several buffers normally exist, only one buffer is designated the @dfn{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. @end ifnottex Buffers in Emacs editing are objects that have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. You can think of the contents of a buffer as a string that you can extend; insertions and deletions may occur in any part of the buffer. @xref{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 accessible only through special-purpose functions. For example, the visited file name 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 @dfn{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 @code{fill-column} or @code{comment-column} in this way. For more information about buffer-local variables and functions related to them, see @ref{Buffer-Local Variables}. For functions and variables related to visiting files in buffers, see @ref{Visiting Files} and @ref{Saving Buffers}. For functions and variables related to the display of buffers in windows, see @ref{Buffers and Windows}. @defun bufferp object This function returns @code{t} if @var{object} is a buffer, @code{nil} otherwise. @end defun @node Current Buffer @section The Current Buffer @cindex selecting a buffer @cindex changing to another buffer @cindex current buffer There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the @dfn{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 (@pxref{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 temporarily designate any buffer as current 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 @code{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 buffer that the command will apply to. (@xref{Command Loop}.) Therefore, @code{set-buffer} is not the way to switch visibly to a different buffer so that the user can edit it. For that, you must use the functions described in @ref{Displaying Buffers}. @strong{Warning:} Lisp functions that change to a different current buffer should not depend 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 @code{set-buffer} within a @code{save-current-buffer} or @code{save-excursion} (@pxref{Excursions}) form that will restore the current buffer when your function is done. Here is an example, the code for the command @code{append-to-buffer} (with the documentation string abridged): @example @group (defun append-to-buffer (buffer start end) "Append to specified buffer the text of the region. @dots{}" (interactive "BAppend to buffer: \nr") (let ((oldbuf (current-buffer))) (save-current-buffer (set-buffer (get-buffer-create buffer)) (insert-buffer-substring oldbuf start end)))) @end group @end example @noindent This function binds a local variable to record the current buffer, and then @code{save-current-buffer} arranges to make it current again. Next, @code{set-buffer} makes the specified buffer current. Finally, @code{insert-buffer-substring} copies the string from the original current buffer to the specified (and now current) buffer. If the buffer appended to happens to be displayed in some window, 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. If you make local bindings (with @code{let} or function arguments) for a variable that may also have buffer-local bindings, make sure that the same buffer is current at the beginning and at the end of the local binding's scope. Otherwise you might bind it in one buffer and unbind it in another! There are two ways to do this. In simple cases, you may see that nothing ever changes the current buffer within the scope of the binding. Otherwise, use @code{save-current-buffer} or @code{save-excursion} to make sure that the buffer current at the beginning is current again whenever the variable is unbound. Do not rely on using @code{set-buffer} to change the current buffer back, because that won't do the job if a quit happens while the wrong buffer is current. Here is what @emph{not} to do: @example @group (let (buffer-read-only (obuf (current-buffer))) (set-buffer @dots{}) @dots{} (set-buffer obuf)) @end group @end example @noindent Using @code{save-current-buffer}, as shown here, handles quitting, errors, and @code{throw}, as well as ordinary evaluation. @example @group (let (buffer-read-only) (save-current-buffer (set-buffer @dots{}) @dots{})) @end group @end example @defun current-buffer This function returns the current buffer. @example @group (current-buffer) @result{} # @end group @end example @end defun @defun set-buffer buffer-or-name This function makes @var{buffer-or-name} the current buffer. This does not display the buffer in any window, so the user cannot necessarily see the buffer. But Lisp programs will now operate on it. This function returns the buffer identified by @var{buffer-or-name}. An error is signaled if @var{buffer-or-name} does not identify an existing buffer. @end defun @defspec save-current-buffer body@dots{} The @code{save-current-buffer} special form saves the identity of the current buffer, evaluates the @var{body} forms, and finally restores that buffer as current. The return value is the value of the last form in @var{body}. The current buffer is restored even in case of an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). If the buffer that used to be current has been killed by the time of exit from @code{save-current-buffer}, then it is not made current again, of course. Instead, whichever buffer was current just before exit remains current. @end defspec @defmac with-current-buffer buffer-or-name body@dots{} The @code{with-current-buffer} macro saves the identity of the current buffer, makes @var{buffer-or-name} current, evaluates the @var{body} forms, and finally restores the buffer. The return value is the value of the last form in @var{body}. The current buffer is restored even in case of an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). An error is signaled if @var{buffer-or-name} does not identify an existing buffer. @end defmac @defmac with-temp-buffer body@dots{} @anchor{Definition of with-temp-buffer} The @code{with-temp-buffer} macro evaluates the @var{body} forms with a temporary buffer as the current buffer. It saves the identity of the current buffer, creates a temporary buffer and makes it current, evaluates the @var{body} forms, and finally restores the previous current buffer while killing the temporary buffer. By default, undo information (@pxref{Undo}) is not recorded in the buffer created by this macro (but @var{body} can enable that, if needed). The return value is the value of the last form in @var{body}. You can return the contents of the temporary buffer by using @code{(buffer-string)} as the last form. The current buffer is restored even in case of an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). See also @code{with-temp-file} in @ref{Definition of with-temp-file,, Writing to Files}. @end defmac @node Buffer Names @section Buffer Names @cindex buffer names Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called @var{buffer-or-name} is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called @var{buffer} must be an actual buffer object, not a name. @cindex hidden buffers @cindex buffers without undo information Buffers that are ephemeral and generally uninteresting to the user have names starting with a space, so that the @code{list-buffers} and @code{buffer-menu} commands don't mention them (but if such a buffer visits a file, it @strong{is} mentioned). A name starting with space also initially disables recording undo information; see @ref{Undo}. @defun buffer-name &optional buffer This function returns the name of @var{buffer} as a string. If @var{buffer} is not supplied, it defaults to the current buffer. If @code{buffer-name} returns @code{nil}, it means that @var{buffer} has been killed. @xref{Killing Buffers}. @example @group (buffer-name) @result{} "buffers.texi" @end group @group (setq foo (get-buffer "temp")) @result{} # @end group @group (kill-buffer foo) @result{} nil @end group @group (buffer-name foo) @result{} nil @end group @group foo @result{} # @end group @end example @end defun @deffn Command rename-buffer newname &optional unique This function renames the current buffer to @var{newname}. An error is signaled if @var{newname} is not a string. @c Emacs 19 feature Ordinarily, @code{rename-buffer} signals an error if @var{newname} is already in use. However, if @var{unique} is non-@code{nil}, it modifies @var{newname} to make a name that is not in use. Interactively, you can make @var{unique} non-@code{nil} with a numeric prefix argument. (This is how the command @code{rename-uniquely} is implemented.) This function returns the name actually given to the buffer. @end deffn @defun get-buffer buffer-or-name This function returns the buffer specified by @var{buffer-or-name}. If @var{buffer-or-name} is a string and there is no buffer with that name, the value is @code{nil}. If @var{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: @example @group (setq b (get-buffer "lewis")) @result{} # @end group @group (get-buffer b) @result{} # @end group @group (get-buffer "Frazzle-nots") @result{} nil @end group @end example See also the function @code{get-buffer-create} in @ref{Creating Buffers}. @end defun @c Emacs 19 feature @defun generate-new-buffer-name starting-name &optional ignore This function returns a name that would be unique for a new buffer---but does not create the buffer. It starts with @var{starting-name}, and produces a name not currently in use for any buffer by appending a number inside of @samp{<@dots{}>}. It starts at 2 and keeps incrementing the number until it is not the name of an existing buffer. If the optional second argument @var{ignore} is non-@code{nil}, it should be a string, a potential buffer name. It means to consider that potential buffer acceptable, if it is tried, even it is the name of an existing buffer (which would normally be rejected). Thus, if buffers named @samp{foo}, @samp{foo<2>}, @samp{foo<3>} and @samp{foo<4>} exist, @example (generate-new-buffer-name "foo") @result{} "foo<5>" (generate-new-buffer-name "foo" "foo<3>") @result{} "foo<3>" (generate-new-buffer-name "foo" "foo<6>") @result{} "foo<5>" @end example See the related function @code{generate-new-buffer} in @ref{Creating Buffers}. @end defun @node Buffer File Name @section Buffer File Name @cindex visited file @cindex buffer file name @cindex file name of buffer The @dfn{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 @code{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. @xref{Visiting Files}. @defun buffer-file-name &optional buffer This function returns the absolute file name of the file that @var{buffer} is visiting. If @var{buffer} is not visiting any file, @code{buffer-file-name} returns @code{nil}. If @var{buffer} is not supplied, it defaults to the current buffer. @example @group (buffer-file-name (other-buffer)) @result{} "/usr/user/lewis/manual/files.texi" @end group @end example @end defun @defvar buffer-file-name This buffer-local variable contains the name of the file being visited in the current buffer, or @code{nil} if it is not visiting a file. It is a permanent local variable, unaffected by @code{kill-all-local-variables}. @example @group buffer-file-name @result{} "/usr/user/lewis/manual/buffers.texi" @end group @end example It is risky to change this variable's value without doing various other things. Normally it is better to use @code{set-visited-file-name} (see below); some of the things done there, such as changing the buffer name, are not strictly necessary, but others are essential to avoid confusing Emacs. @end defvar @defvar buffer-file-truename This buffer-local variable holds the abbreviated truename of the file visited in the current buffer, or @code{nil} if no file is visited. It is a permanent local, unaffected by @code{kill-all-local-variables}. @xref{Truenames}, and @ref{Definition of abbreviate-file-name}. @end defvar @defvar buffer-file-number This buffer-local variable holds the file number and directory device number of the file visited in the current buffer, or @code{nil} if no file or a nonexistent file is visited. It is a permanent local, unaffected by @code{kill-all-local-variables}. The value is normally a list of the form @code{(@var{filenum} @var{devnum})}. This pair of numbers uniquely identifies the file among all files accessible on the system. See the function @code{file-attributes}, in @ref{File Attributes}, for more information about them. If @code{buffer-file-name} is the name of a symbolic link, then both numbers refer to the recursive target. @end defvar @defun get-file-buffer filename This function returns the buffer visiting file @var{filename}. If there is no such buffer, it returns @code{nil}. The argument @var{filename}, which must be a string, is expanded (@pxref{File Name Expansion}), then compared against the visited file names of all live buffers. Note that the buffer's @code{buffer-file-name} must match the expansion of @var{filename} exactly. This function will not recognize other names for the same file. @example @group (get-file-buffer "buffers.texi") @result{} # @end group @end example 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. @end defun @defun find-buffer-visiting filename &optional predicate This is like @code{get-file-buffer}, except that it can return any buffer visiting the file @emph{possibly under a different name}. That is, the buffer's @code{buffer-file-name} does not need to match the expansion of @var{filename} exactly, it only needs to refer to the same file. If @var{predicate} is non-@code{nil}, it should be a function of one argument, a buffer visiting @var{filename}. The buffer is only considered a suitable return value if @var{predicate} returns non-@code{nil}. If it can not find a suitable buffer to return, @code{find-buffer-visiting} returns @code{nil}. @end defun @deffn Command set-visited-file-name filename &optional no-query along-with-file If @var{filename} is a non-empty string, this function changes the name of the file visited in the current buffer to @var{filename}. (If the buffer had no visited file, this gives it one.) The @emph{next time} the buffer is saved it will go in the newly-specified file. This command marks the buffer as modified, since it does not (as far as Emacs knows) match the contents of @var{filename}, even if it matched the former visited file. It also renames the buffer to correspond to the new file name, unless the new name is already in use. If @var{filename} is @code{nil} or the empty string, that stands for ``no visited file.'' In this case, @code{set-visited-file-name} marks the buffer as having no visited file, without changing the buffer's modified flag. Normally, this function asks the user for confirmation if there already is a buffer visiting @var{filename}. If @var{no-query} is non-@code{nil}, that prevents asking this question. If there already is a buffer visiting @var{filename}, and the user confirms or @var{query} is non-@code{nil}, this function makes the new buffer name unique by appending a number inside of @samp{<@dots{}>} to @var{filename}. If @var{along-with-file} is non-@code{nil}, that means to assume that the former visited file has been renamed to @var{filename}. In this case, the command does not change the buffer's modified flag, nor the buffer's recorded last file modification time as reported by @code{visited-file-modtime} (@pxref{Modification Time}). If @var{along-with-file} is @code{nil}, this function clears the recorded last file modification time, after which @code{visited-file-modtime} returns zero. @c Wordy to avoid overfull hbox. --rjc 16mar92 When the function @code{set-visited-file-name} is called interactively, it prompts for @var{filename} in the minibuffer. @end deffn @defvar list-buffers-directory This buffer-local variable specifies a string to display in a buffer listing where the visited file name would go, for buffers that don't have a visited file name. Dired buffers use this variable. @end defvar @node Buffer Modification @section Buffer Modification @cindex buffer modification @cindex modification flag (of buffer) Emacs keeps a flag called the @dfn{modified flag} for each buffer, to record whether you have changed the text of the buffer. This flag is set to @code{t} whenever you alter the contents of the buffer, and cleared to @code{nil} when you save it. Thus, the flag shows whether there are unsaved changes. The flag value is normally shown in the mode line (@pxref{Mode Line Variables}), and controls saving (@pxref{Saving Buffers}) and auto-saving (@pxref{Auto-Saving}). Some Lisp programs set the flag explicitly. For example, the function @code{set-visited-file-name} sets the flag to @code{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 @ref{Text}. @defun buffer-modified-p &optional buffer This function returns @code{t} if the buffer @var{buffer} has been modified since it was last read in from a file or saved, or @code{nil} otherwise. If @var{buffer} is not supplied, the current buffer is tested. @end defun @defun set-buffer-modified-p flag This function marks the current buffer as modified if @var{flag} is non-@code{nil}, or as unmodified if the flag is @code{nil}. Another effect of calling this function is to cause unconditional redisplay of the mode line for the current buffer. In fact, the function @code{force-mode-line-update} works by doing this: @example @group (set-buffer-modified-p (buffer-modified-p)) @end group @end example @end defun @defun restore-buffer-modified-p flag Like @code{set-buffer-modified-p}, but does not force redisplay of mode lines. @end defun @deffn Command not-modified &optional arg This command marks the current buffer as unmodified, and not needing to be saved. If @var{arg} is non-@code{nil}, it marks the buffer as modified, so that it will be saved at the next suitable occasion. Interactively, @var{arg} is the prefix argument. Don't use this function in programs, since it prints a message in the echo area; use @code{set-buffer-modified-p} (above) instead. @end deffn @defun buffer-modified-tick &optional buffer This function returns @var{buffer}'s modification-count. This is a counter that increments every time the buffer is modified. If @var{buffer} is @code{nil} (or omitted), the current buffer is used. The counter can wrap around occasionally. @end defun @defun buffer-chars-modified-tick &optional buffer This function returns @var{buffer}'s character-change modification-count. Changes to text properties leave this counter unchanged; however, each time text is inserted or removed from the buffer, the counter is reset to the value that would be returned @code{buffer-modified-tick}. By comparing the values returned by two @code{buffer-chars-modified-tick} calls, you can tell whether a character change occurred in that buffer in between the calls. If @var{buffer} is @code{nil} (or omitted), the current buffer is used. @end defun @node Modification Time @comment node-name, next, previous, up @section Buffer Modification Time @cindex comparing file modification time @cindex modification time of buffer 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. (@xref{File Attributes}, for how to examine a file's modification time.) @defun verify-visited-file-modtime buffer This function compares what @var{buffer} has recorded for the modification time of its visited file against the actual modification time of the file as recorded by the operating system. The two should be the same unless some other process has written the file since Emacs visited or saved it. The function returns @code{t} if the last actual modification time and Emacs's recorded modification time are the same, @code{nil} otherwise. It also returns @code{t} if the buffer has no recorded last modification time, that is if @code{visited-file-modtime} would return zero. It always returns @code{t} for buffers that are not visiting a file, even if @code{visited-file-modtime} returns a non-zero value. For instance, it always returns @code{t} for dired buffers. It returns @code{t} for buffers that are visiting a file that does not exist and never existed, but @code{nil} for file-visiting buffers whose file has been deleted. @end defun @defun 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 @code{set-visited-file-name} and other exceptional places where the usual test to avoid overwriting a changed file should not be done. @end defun @c Emacs 19 feature @defun visited-file-modtime This function returns the current buffer's recorded last file modification time, as a list of the form @code{(@var{high} @var{low})}. (This is the same format that @code{file-attributes} uses to return time values; see @ref{File Attributes}.) If the buffer has no recorded last modification time, this function returns zero. This case occurs, for instance, if the buffer is not visiting a file or if the time has been explicitly cleared by @code{clear-visited-file-modtime}. Note, however, that @code{visited-file-modtime} returns a list for some non-file buffers too. For instance, in a Dired buffer listing a directory, it returns the last modification time of that directory, as recorded by Dired. For a new buffer visiting a not yet existing file, @var{high} is @minus{}1 and @var{low} is 65535, that is, @ifnottex @w{2**16 - 1.} @end ifnottex @tex @math{2^{16}-1}. @end tex @end defun @c Emacs 19 feature @defun set-visited-file-modtime &optional time This function updates the buffer's record of the last modification time of the visited file, to the value specified by @var{time} if @var{time} is not @code{nil}, and otherwise to the last modification time of the visited file. If @var{time} is neither @code{nil} nor zero, it should have the form @code{(@var{high} . @var{low})} or @code{(@var{high} @var{low})}, in either case containing two integers, each of which holds 16 bits of the time. This function is useful if the buffer was not read from the file normally, or if the file itself has been changed for some known benign reason. @end defun @defun ask-user-about-supersession-threat filename This function is used to ask a user how to proceed after an attempt to modify an buffer visiting file @var{filename} when the file is newer than the buffer text. Emacs detects this because the modification time of the file on disk is newer than the last save-time of the buffer. This means some other program has probably altered the file. @kindex file-supersession 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 @code{file-supersession} error with data @code{(@var{filename})}, in which case the proposed buffer modification is not allowed. This function is called automatically by Emacs on the proper occasions. It exists so you can customize Emacs by redefining it. See the file @file{userlock.el} for the standard definition. See also the file locking mechanism in @ref{File Locks}. @end defun @node Read Only Buffers @section Read-Only Buffers @cindex read-only buffer @cindex buffer, read-only If a buffer is @dfn{read-only}, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing. Read-only buffers are used in two kinds of situations: @itemize @bullet @item A buffer visiting a write-protected file is normally read-only. Here, the purpose is to inform 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 @kbd{C-x C-q}. @item Modes such as Dired and Rmail make buffers read-only when altering the contents with the usual editing commands would probably be a mistake. The special commands of these modes bind @code{buffer-read-only} to @code{nil} (with @code{let}) or bind @code{inhibit-read-only} to @code{t} around the places where they themselves change the text. @end itemize @defvar buffer-read-only This buffer-local variable specifies whether the buffer is read-only. The buffer is read-only if this variable is non-@code{nil}. @end defvar @defvar inhibit-read-only If this variable is non-@code{nil}, then read-only buffers and, depending on the actual value, some or all read-only characters may be modified. Read-only characters in a buffer are those that have non-@code{nil} @code{read-only} properties (either text properties or overlay properties). @xref{Special Properties}, for more information about text properties. @xref{Overlays}, for more information about overlays and their properties. If @code{inhibit-read-only} is @code{t}, all @code{read-only} character properties have no effect. If @code{inhibit-read-only} is a list, then @code{read-only} character properties have no effect if they are members of the list (comparison is done with @code{eq}). @end defvar @deffn Command toggle-read-only &optional arg This command toggles whether the current buffer is read-only. It is intended for interactive use; do not 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 @code{buffer-read-only} explicitly to the proper value, @code{t} or @code{nil}. If @var{arg} is non-@code{nil}, it should be a raw prefix argument. @code{toggle-read-only} sets @code{buffer-read-only} to @code{t} if the numeric value of that prefix argument is positive and to @code{nil} otherwise. @xref{Prefix Command Arguments}. @end deffn @defun barf-if-buffer-read-only This function signals a @code{buffer-read-only} error if the current buffer is read-only. @xref{Using Interactive}, for another way to signal an error if the current buffer is read-only. @end defun @node The Buffer List @section The Buffer List @cindex buffer list The @dfn{buffer list} is a list of all live buffers. The order of the buffers in the list is based primarily on how recently each buffer has been displayed in a window. Several functions, notably @code{other-buffer}, use this ordering. A buffer list displayed for the user also follows this order. Creating a buffer adds it to the end of the buffer list, and killing a buffer removes it. Buffers move to the front of the list when they are selected for display in a window (@pxref{Displaying Buffers}), and to the end when they are buried (see @code{bury-buffer}, below). There are no functions available to the Lisp programmer which directly manipulate the buffer list. In addition to the fundamental Emacs buffer list, each frame has its own version of the buffer list, in which the buffers that have been selected in that frame come first, starting with the buffers most recently selected @emph{in that frame}. (This order is recorded in @var{frame}'s @code{buffer-list} frame parameter; see @ref{Buffer Parameters}.) The buffers that were never selected in @var{frame} come afterward, ordered according to the fundamental Emacs buffer list. @defun buffer-list &optional frame This function returns the buffer list, including all buffers, even those whose names begin with a space. The elements are actual buffers, not their names. If @var{frame} is a frame, this returns @var{frame}'s buffer list. If @var{frame} is @code{nil}, the fundamental Emacs buffer list is used: all the buffers appear in order of most recent selection, regardless of which frames they were selected in. @example @group (buffer-list) @result{} (# # # # #) @end group @group ;; @r{Note that the name of the minibuffer} ;; @r{begins with a space!} (mapcar (function buffer-name) (buffer-list)) @result{} ("buffers.texi" " *Minibuf-1*" "buffer.c" "*Help*" "TAGS") @end group @end example @end defun The list that @code{buffer-list} returns is constructed specifically by @code{buffer-list}; it is not an internal Emacs data structure, and modifying it has no effect on the order of buffers. If you want to change the order of buffers in the frame-independent buffer list, here is an easy way: @example (defun reorder-buffer-list (new-list) (while new-list (bury-buffer (car new-list)) (setq new-list (cdr new-list)))) @end example With this method, you can specify any order for the list, but there is no danger of losing a buffer or adding something that is not a valid live buffer. To change the order or value of a frame's buffer list, set the frame's @code{buffer-list} frame parameter with @code{modify-frame-parameters} (@pxref{Parameter Access}). @defun other-buffer &optional buffer visible-ok frame This function returns the first buffer in the buffer list other than @var{buffer}. Usually this is the buffer selected most recently (in frame @var{frame} or else the currently selected frame, @pxref{Input Focus}), aside from @var{buffer}. Buffers whose names start with a space are not considered at all. If @var{buffer} is not supplied (or if it is not a buffer), then @code{other-buffer} returns the first buffer in the selected frame's buffer list that is not now visible in any window in a visible frame. If @var{frame} has a non-@code{nil} @code{buffer-predicate} parameter, then @code{other-buffer} uses that predicate to decide which buffers to consider. It calls the predicate once for each buffer, and if the value is @code{nil}, that buffer is ignored. @xref{Buffer Parameters}. @c Emacs 19 feature If @var{visible-ok} is @code{nil}, @code{other-buffer} avoids returning a buffer visible in any window on any visible frame, except as a last resort. If @var{visible-ok} is non-@code{nil}, then it does not matter whether a buffer is displayed somewhere or not. If no suitable buffer exists, the buffer @samp{*scratch*} is returned (and created, if necessary). @end defun @deffn Command bury-buffer &optional buffer-or-name This function puts @var{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 @code{other-buffer} to return. The argument can be either a buffer itself or the name of one. @code{bury-buffer} operates on each frame's @code{buffer-list} parameter as well as the frame-independent Emacs buffer list; therefore, the buffer that you bury will come last in the value of @code{(buffer-list @var{frame})} and in the value of @code{(buffer-list nil)}. If @var{buffer-or-name} is @code{nil} or omitted, this means to bury the current buffer. In addition, if the buffer is displayed in the selected window, this switches to some other buffer (obtained using @code{other-buffer}) in the selected window. But if the buffer is displayed in some other window, it remains displayed there. To replace a buffer in all the windows that display it, use @code{replace-buffer-in-windows}. @xref{Buffers and Windows}. @end deffn @node Creating Buffers @section Creating Buffers @cindex creating buffers @cindex buffers, creating This section describes the two primitives for creating buffers. @code{get-buffer-create} creates a buffer if it finds no existing buffer with the specified name; @code{generate-new-buffer} always creates a new buffer and gives it a unique name. Other functions you can use to create buffers include @code{with-output-to-temp-buffer} (@pxref{Temporary Displays}) and @code{create-file-buffer} (@pxref{Visiting Files}). Starting a subprocess can also create a buffer (@pxref{Processes}). @defun get-buffer-create name This function returns a buffer named @var{name}. It returns a live buffer with that name, if one exists; otherwise, it creates a new buffer. The buffer does not become the current buffer---this function does not change which buffer is current. If @var{name} is a buffer instead of a string, it is returned, even if it is dead. An error is signaled if @var{name} is neither a string nor a buffer. @example @group (get-buffer-create "foo") @result{} # @end group @end example The major mode for a newly created buffer is set to Fundamental mode. (The variable @code{default-major-mode} is handled at a higher level; see @ref{Auto Major Mode}.) If the name begins with a space, the buffer initially disables undo information recording (@pxref{Undo}). @end defun @defun generate-new-buffer name This function returns a newly created, empty buffer, but does not make it current. If there is no buffer named @var{name}, then that is the name of the new buffer. If that name is in use, this function adds suffixes of the form @samp{<@var{n}>} to @var{name}, where @var{n} is an integer. It tries successive integers starting with 2 until it finds an available name. An error is signaled if @var{name} is not a string. @example @group (generate-new-buffer "bar") @result{} # @end group @group (generate-new-buffer "bar") @result{} #> @end group @group (generate-new-buffer "bar") @result{} #> @end group @end example The major mode for the new buffer is set to Fundamental mode. The variable @code{default-major-mode} is handled at a higher level. @xref{Auto Major Mode}. See the related function @code{generate-new-buffer-name} in @ref{Buffer Names}. @end defun @node Killing Buffers @section Killing Buffers @cindex killing buffers @cindex buffers, killing @dfn{Killing a buffer} makes its name unknown to Emacs and makes the memory space it occupied available for other use. The buffer object for the buffer that 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; if you kill two distinct buffers, they remain distinct according to @code{eq} although both are dead. If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can in general change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn't current). @xref{Current Buffer}. If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect buffers are automatically killed as well. The @code{buffer-name} of a killed buffer is @code{nil}. You can use this feature to test whether a buffer has been killed: @example @group (defun buffer-killed-p (buffer) "Return t if BUFFER is killed." (not (buffer-name buffer))) @end group @end example @deffn Command kill-buffer buffer-or-name This function kills the buffer @var{buffer-or-name}, freeing all its memory for other uses or to be returned to the operating system. If @var{buffer-or-name} is @code{nil}, it kills the current buffer. Any processes that have this buffer as the @code{process-buffer} are sent the @code{SIGHUP} signal, which normally causes them to terminate. (The basic meaning of @code{SIGHUP} is that a dialup line has been disconnected.) @xref{Signals to Processes}. If the buffer is visiting a file and contains unsaved changes, @code{kill-buffer} asks the user to confirm before the buffer is killed. It does this even if not called interactively. To prevent the request for confirmation, clear the modified flag before calling @code{kill-buffer}. @xref{Buffer Modification}. Killing a buffer that is already dead has no effect. This function returns @code{t} if it actually killed the buffer. It returns @code{nil} if the user refuses to confirm or if @var{buffer-or-name} was already dead. @smallexample (kill-buffer "foo.unchanged") @result{} t (kill-buffer "foo.changed") ---------- Buffer: Minibuffer ---------- Buffer foo.changed modified; kill anyway? (yes or no) @kbd{yes} ---------- Buffer: Minibuffer ---------- @result{} t @end smallexample @end deffn @defvar kill-buffer-query-functions After confirming unsaved changes, @code{kill-buffer} calls the functions in the list @code{kill-buffer-query-functions}, in order of appearance, with no arguments. The buffer being killed is the current buffer when they are called. The idea of this feature is that these functions will ask for confirmation from the user. If any of them returns @code{nil}, @code{kill-buffer} spares the buffer's life. @end defvar @defvar kill-buffer-hook This is a normal hook run by @code{kill-buffer} after asking all the questions it is going to ask, just before actually killing the buffer. The buffer to be killed is current when the hook functions run. @xref{Hooks}. This variable is a permanent local, so its local binding is not cleared by changing major modes. @end defvar @defvar buffer-offer-save This variable, if non-@code{nil} in a particular buffer, tells @code{save-buffers-kill-emacs} and @code{save-some-buffers} (if the second optional argument to that function is @code{t}) to offer to save that buffer, just as they offer to save file-visiting buffers. @xref{Definition of save-some-buffers}. The variable @code{buffer-offer-save} automatically becomes buffer-local when set for any reason. @xref{Buffer-Local Variables}. @end defvar @defvar buffer-save-without-query This variable, if non-@code{nil} in a particular buffer, tells @code{save-buffers-kill-emacs} and @code{save-some-buffers} to save this buffer (if it's modified) without asking the user. The variable automatically becomes buffer-local when set for any reason. @end defvar @defun buffer-live-p object This function returns @code{t} if @var{object} is a buffer which has not been killed, @code{nil} otherwise. @end defun @node Indirect Buffers @section Indirect Buffers @cindex indirect buffers @cindex base buffer An @dfn{indirect buffer} shares the text of some other buffer, which is called the @dfn{base buffer} of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer. The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves. In all other respects, the indirect buffer and its base buffer are completely separate. They have different names, independent values of point, independent narrowing, independent markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), independent major modes, and independent buffer-local variable bindings. An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually saves the base buffer. Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer. @deffn Command make-indirect-buffer base-buffer name &optional clone This creates and returns an indirect buffer named @var{name} whose base buffer is @var{base-buffer}. The argument @var{base-buffer} may be a live buffer or the name (a string) of an existing buffer. If @var{name} is the name of an existing buffer, an error is signaled. If @var{clone} is non-@code{nil}, then the indirect buffer originally shares the ``state'' of @var{base-buffer} such as major mode, minor modes, buffer local variables and so on. If @var{clone} is omitted or @code{nil} the indirect buffer's state is set to the default state for new buffers. If @var{base-buffer} is an indirect buffer, its base buffer is used as the base for the new buffer. If, in addition, @var{clone} is non-@code{nil}, the initial state is copied from the actual base buffer, not from @var{base-buffer}. @end deffn @defun clone-indirect-buffer newname display-flag &optional norecord This function creates and returns a new indirect buffer that shares the current buffer's base buffer and copies the rest of the current buffer's attributes. (If the current buffer is not indirect, it is used as the base buffer.) If @var{display-flag} is non-@code{nil}, that means to display the new buffer by calling @code{pop-to-buffer}. If @var{norecord} is non-@code{nil}, that means not to put the new buffer to the front of the buffer list. @end defun @defun buffer-base-buffer &optional buffer This function returns the base buffer of @var{buffer}, which defaults to the current buffer. If @var{buffer} is not indirect, the value is @code{nil}. Otherwise, the value is another buffer, which is never an indirect buffer. @end defun @node Buffer Gap @section The Buffer Gap Emacs buffers are implemented using an invisible @dfn{gap} to make insertion and deletion faster. Insertion works by filling in part of the gap, and deletion adds to the gap. Of course, this means that the gap must first be moved to the locus of the insertion or deletion. Emacs moves the gap only when you try to insert or delete. This is why your first editing command in one part of a large buffer, after previously editing in another far-away part, sometimes involves a noticeable delay. This mechanism works invisibly, and Lisp code should never be affected by the gap's current location, but these functions are available for getting information about the gap status. @defun gap-position This function returns the current gap position in the current buffer. @end defun @defun gap-size This function returns the current gap size of the current buffer. @end defun @ignore arch-tag: 2e53cfab-5691-41f6-b5a8-9c6a3462399c @end ignore