This is Info file elisp, produced by Makeinfo-1.55 from the input file elisp.texi. This version is the edition 2.3 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 19.23. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992, 1993, 1994 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. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and 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 the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English.  File: elisp, Node: The Mark, Next: The Region, Prev: Changing Markers, Up: Markers The Mark ======== One special marker in each buffer is designated "the mark". It records a position for the user for the sake of commands such as `C-w' and `C-x TAB'. Lisp programs should set the mark only to values that have a potential use to the user, and never for their own internal purposes. For example, the `replace-regexp' command sets the mark to the value of point before doing any replacements, because this enables the user to move back there conveniently after the replace is finished. Many commands are designed so that when called interactively they operate on the text between point and the mark. If you are writing such a command, don't examine the mark directly; instead, use `interactive' with the `r' specification. This provides the values of point and the mark as arguments to the command in an interactive call, but permits other Lisp programs to specify arguments explicitly. *Note Interactive Codes::. Each buffer has its own value of the mark that is independent of the value of the mark in other buffers. When a buffer is created, the mark exists but does not point anywhere. We consider this state as "the absence of a mark in that buffer". Once the mark "exists" in a buffer, it normally never ceases to exist. However, it may become "inactive", if Transient Mark mode is enabled. The variable `mark-active', which is always local in all buffers, indicates whether the mark is active: non-`nil' means yes. A command can request deactivation of the mark upon return to the editor command loop by setting `deactivate-mark' to a non-`nil' value (but this deactivation only follows if Transient Mark mode is enabled). The main motivation for using Transient Mark mode is that this mode also enables highlighting of the region when the mark is active. *Note Display::. In addition to the mark, each buffer has a "mark ring" which is a list of markers containing previous values of the mark. When editing commands change the mark, they should normally save the old value of the mark on the mark ring. The variable `mark-ring-max' specifies the maximum number of entries in the mark ring; once the list becomes this long, adding a new element deletes the last element. - Function: mark &optional FORCE This function returns the current buffer's mark position as an integer. If the mark is inactive, `mark' normally signals an error. However, if FORCE is non-`nil', then `mark' returns the mark position anyway--or `nil', if the mark is not yet set for this buffer. - Function: mark-marker This function returns the current buffer's mark. This is the very marker which records the mark location inside Emacs, not a copy. Therefore, changing this marker's position will directly affect the position of the mark. Don't do it unless that is the effect you want. (setq m (mark-marker)) => # (set-marker m 100) => # (mark-marker) => # Like any marker, this marker can be set to point at any buffer you like. We don't recommend that you make it point at any buffer other than the one of which it is the mark. If you do, it will yield perfectly consistent, but rather odd, results. - Function: set-mark POSITION This function sets the mark to POSITION, and activates the mark. The old value of the mark is *not* pushed onto the mark ring. *Please note:* use this function only if you want the user to see that the mark has moved, and you want the previous mark position to be lost. Normally, when a new mark is set, the old one should go on the `mark-ring'. For this reason, most applications should use `push-mark' and `pop-mark', not `set-mark'. Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user's convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example: (let ((beg (point))) (forward-line 1) (delete-region beg (point))). - Function: push-mark &optional POSITION NOMSG ACTIVATE This function sets the current buffer's mark to POSITION, and pushes a copy of the previous mark onto `mark-ring'. If POSITION is `nil', then the value of point is used. `push-mark' returns `nil'. The function `push-mark' normally *does not* activate the mark. To do that, specify `t' for the argument ACTIVATE. A `Mark set' message is displayed unless NOMSG is non-`nil'. - Function: pop-mark This function pops off the top element of `mark-ring' and makes that mark become the buffer's actual mark. This does not move point in the buffer, and it does nothing if `mark-ring' is empty. It deactivates the mark. The return value is not meaningful. - User Option: transient-mark-mode This variable enables Transient Mark mode, in which every buffer-modifying primitive sets `deactivate-mark'. The consequence of this is that commands that modify the buffer normally make the mark inactive. - Variable: deactivate-mark If an editor command sets this variable non-`nil', then the editor command loop deactivates the mark after the command returns. - Variable: mark-active The mark is active when this variable is non-`nil'. This variable is always local in each buffer. - Variable: activate-mark-hook - Variable: deactivate-mark-hook These normal hooks are run, respectively, when the mark becomes active and when it becomes inactive. The hook `activate-mark-hook' is also run at the end of a command if the mark is active and the region may have changed. - Variable: mark-ring The value of this buffer-local variable is the list of saved former marks of the current buffer, most recent first. mark-ring => (# # ...) - User Option: mark-ring-max The value of this variable is the maximum size of `mark-ring'. If more marks than this are pushed onto the `mark-ring', `push-mark' discards an old mark when it adds a new one.  File: elisp, Node: The Region, Prev: The Mark, Up: Markers The Region ========== The text between point and the mark is known as "the region". Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here. - Function: region-beginning This function returns the position of the beginning of the region (as an integer). This is the position of either point or the mark, whichever is smaller. If the mark does not point anywhere, an error is signaled. - Function: region-end This function returns the position of the end of the region (as an integer). This is the position of either point or the mark, whichever is larger. If the mark does not point anywhere, an error is signaled. Few programs need to use the `region-beginning' and `region-end' functions. A command designed to operate on a region should normally use `interactive' with the `r' specification to find the beginning and end of the region. This lets other Lisp programs specify the bounds explicitly as arguments. (*Note Interactive Codes::.)  File: elisp, Node: Text, Next: Searching and Matching, Prev: Markers, Up: Top Text **** This chapter describes the functions that deal with the text in a buffer. Most examine, insert or delete text in the current buffer, often in the vicinity of point. Many are interactive. All the functions that change the text provide for undoing the changes (*note Undo::.). Many text-related functions operate on a region of text defined by two buffer positions passed in arguments named START and END. These arguments should be either markers (*note Markers::.) or numeric character positions (*note Positions::.). The order of these arguments does not matter; it is all right for START to be the end of the region and END the beginning. For example, `(delete-region 1 10)' and `(delete-region 10 1)' are equivalent. An `args-out-of-range' error is signaled if either START or END is outside the accessible portion of the buffer. In an interactive call, point and the mark are used for these arguments. Throughout this chapter, "text" refers to the characters in the buffer. * Menu: * Near Point:: Examining text in the vicinity of point. * Buffer Contents:: Examining text in a general fashion. * Comparing Text:: Comparing substrings of buffers. * Insertion:: Adding new text to a buffer. * Commands for Insertion:: User-level commands to insert text. * Deletion:: Removing text from a buffer. * User-Level Deletion:: User-level commands to delete text. * The Kill Ring:: Where removed text sometimes is saved for later use. * Undo:: Undoing changes to the text of a buffer. * Maintaining Undo:: How to enable and disable undo information. How to control how much information is kept. * Filling:: Functions for explicit filling. * Auto Filling:: How auto-fill mode is implemented to break lines. * Sorting:: Functions for sorting parts of the buffer. * Columns:: Computing horizontal positions, and using them. * Indentation:: Functions to insert or adjust indentation. * Case Changes:: Case conversion of parts of the buffer. * Text Properties:: Assigning Lisp property lists to text characters. * Substitution:: Replacing a given character wherever it appears. * Transposition:: Swapping two portions of a buffer. * Registers:: How registers are implemented. Accessing the text or position stored in a register. * Change Hooks:: Supplying functions to be run when text is changed.  File: elisp, Node: Near Point, Next: Buffer Contents, Up: Text Examining Text Near Point ========================= Many functions are provided to look at the characters around point. Several simple functions are described here. See also `looking-at' in *Note Regexp Search::. - Function: char-after POSITION This function returns the character in the current buffer at (i.e., immediately after) position POSITION. If POSITION is out of range for this purpose, either before the beginning of the buffer, or at or beyond the end, then the value is `nil'. In the following example, assume that the first character in the buffer is `@': (char-to-string (char-after 1)) => "@" - Function: following-char This function returns the character following point in the current buffer. This is similar to `(char-after (point))'. However, if point is at the end of the buffer, then `following-char' returns 0. Remember that point is always between characters, and the terminal cursor normally appears over the character following point. Therefore, the character returned by `following-char' is the character the cursor is over. In this example, point is between the `a' and the `c'. ---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (char-to-string (preceding-char)) => "a" (char-to-string (following-char)) => "c" - Function: preceding-char This function returns the character preceding point in the current buffer. See above, under `following-char', for an example. If point is at the beginning of the buffer, `preceding-char' returns 0. - Function: bobp This function returns `t' if point is at the beginning of the buffer. If narrowing is in effect, this means the beginning of the accessible portion of the text. See also `point-min' in *Note Point::. - Function: eobp This function returns `t' if point is at the end of the buffer. If narrowing is in effect, this means the end of accessible portion of the text. See also `point-max' in *Note Point::. - Function: bolp This function returns `t' if point is at the beginning of a line. *Note Text Lines::. The beginning of the buffer (or its accessible portion always counts as the beginning of a line. - Function: eolp This function returns `t' if point is at the end of a line. The end of the buffer (or of its accessible portion) is always considered the end of a line.  File: elisp, Node: Buffer Contents, Next: Comparing Text, Prev: Near Point, Up: Text Examining Buffer Contents ========================= This section describes two functions that allow a Lisp program to convert any portion of the text in the buffer into a string. - Function: buffer-substring START END This function returns a string containing a copy of the text of the region defined by positions START and END in the current buffer. If the arguments are not positions in the accessible portion of the buffer, `buffer-substring' signals an `args-out-of-range' error. It is not necessary for START to be less than END; the arguments can be given in either order. But most often the smaller argument is written first. ---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-substring 1 10) => "This is t" (buffer-substring (point-max) 10) => "he contents of buffer foo " - Function: buffer-string This function returns the contents of the accessible portion of the current buffer as a string. This is the portion between `(point-min)' and `(point-max)' (*note Narrowing::.). ---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-string) => "This is the contents of buffer foo "  File: elisp, Node: Comparing Text, Next: Insertion, Prev: Buffer Contents, Up: Text Comparing Text ============== This function lets you compare portions of the text in a buffer, without copying them into strings first. - Function: compare-buffer-substrings BUFFER1 START1 END1 BUFFER2 START2 END2 This function lets you compare two substrings of the same buffer or two different buffers. The first three arguments specify one substring, giving a buffer and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use `nil' for BUFFER1, BUFFER2 or both to stand for the current buffer. The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings. This function ignores case when comparing characters if `case-fold-search' is non-`nil'. Suppose the current buffer contains the text `foobarbar haha!rara!'; then in this example the two substrings are `rbar ' and `rara!'. The value is 2 because the first substring is greater at the second character. (compare-buffer-substring nil 6 11 nil 16 21) => 2 This function does not exist in Emacs version 18 and earlier.  File: elisp, Node: Insertion, Next: Commands for Insertion, Prev: Comparing Text, Up: Text Insertion ========= "Insertion" means adding new text to a buffer. The inserted text goes at point--between the character before point and the character after point. Insertion relocates markers that point at positions after the insertion point, so that they stay with the surrounding text (*note Markers::.). When a marker points at the place of insertion, insertion normally doesn't relocate the marker, so that it points to the beginning of the inserted text; however, certain special functions such as `insert-before-markers' relocate such markers to point after the inserted text. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the latter insertion "before point". Insertion functions signal an error if the current buffer is read-only. - Function: insert &rest ARGS This function inserts the strings and/or characters ARGS into the current buffer, at point, moving point forward. An error is signaled unless all ARGS are either strings or characters. The value is `nil'. - Function: insert-before-markers &rest ARGS This function inserts the strings and/or characters ARGS into the current buffer, at point, moving point forward. An error is signaled unless all ARGS are either strings or characters. The value is `nil'. This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text. - Function: insert-char CHARACTER COUNT This function inserts COUNT instances of CHARACTER into the current buffer before point. The argument COUNT must be a number, and CHARACTER must be a character. The value is `nil'. - Function: insert-buffer-substring FROM-BUFFER-OR-NAME &optional START END This function inserts a portion of buffer FROM-BUFFER-OR-NAME (which must already exist) into the current buffer before point. The text inserted is the region from START and END. (These arguments default to the beginning and end of the accessible portion of that buffer.) This function returns `nil'. In this example, the form is executed with buffer `bar' as the current buffer. We assume that buffer `bar' is initially empty. ---------- Buffer: foo ---------- We hold these truths to be self-evident, that all ---------- Buffer: foo ---------- (insert-buffer-substring "foo" 1 20) => nil ---------- Buffer: bar ---------- We hold these truth ---------- Buffer: bar ---------- *Note Sticky Properties::, for other insertion functions that inherit text properties from the nearby text.  File: elisp, Node: Commands for Insertion, Next: Deletion, Prev: Insertion, Up: Text User-Level Insertion Commands ============================= This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs. - Command: insert-buffer FROM-BUFFER-OR-NAME This command inserts the entire contents of FROM-BUFFER-OR-NAME (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is `nil'. - Command: self-insert-command COUNT This command inserts the last character typed COUNT times and returns `nil'. Most printing characters are bound to this command. In routine use, `self-insert-command' is the most frequently called function in Emacs, but programs rarely use it except to install it on a keymap. In an interactive call, COUNT is the numeric prefix argument. This function calls `auto-fill-function' if the current column number is greater than the value of `fill-column' and the character inserted is a space (*note Auto Filling::.). This function performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (*Note Abbrevs::, and *Note Syntax Class Table::.) This function is also responsible for calling `blink-paren-function' when the inserted character has close parenthesis syntax (*note Blinking::.). - Command: newline &optional NUMBER-OF-NEWLINES This command inserts newlines into the current buffer before point. If NUMBER-OF-NEWLINES is supplied, that many newline characters are inserted. In Auto Fill mode, `newline' can break the preceding line if NUMBER-OF-NEWLINES is not supplied. When this happens, it actually inserts two newlines at different places: one at point, and another earlier in the line. `newline' does not auto-fill if NUMBER-OF-NEWLINES is non-`nil'. The value returned is `nil'. In an interactive call, COUNT is the numeric prefix argument. - Command: split-line This command splits the current line, moving the portion of the line after point down vertically, so that it is on the next line directly below where it was before. Whitespace is inserted as needed at the beginning of the lower line, using the `indent-to' function. `split-line' returns the position of point. Programs hardly ever use this function. - Variable: overwrite-mode This variable controls whether overwrite mode is in effect: a non-`nil' value enables the mode. It is automatically made buffer-local when set in any fashion.  File: elisp, Node: Deletion, Next: User-Level Deletion, Prev: Commands for Insertion, Up: Text Deletion of Text ================ Deletion means removing part of the text in a buffer, without saving it in the kill ring (*note The Kill Ring::.). Deleted text can't be yanked, but can be reinserted using the undo mechanism (*note Undo::.). Some deletion functions save text in the kill ring in some cases but not in the usual case. All of the deletion functions operate on the current buffer, and all return a value of `nil'. - Function: erase-buffer This function deletes the entire text of the current buffer, leaving it empty. If the buffer is read-only, it signals a `buffer-read-only' error. Otherwise, it deletes the text without asking for any confirmation. It returns `nil'. Normally, deleting a large amount of text from a buffer inhibits further auto-saving of that buffer "because it has shrunk". However, `erase-buffer' does not do this, the idea being that the future text is not really related to the former text, and its size should not be compared with that of the former text. - Command: delete-region START END This command deletes the text in the current buffer in the region defined by START and END. The value is `nil'. - Command: delete-char COUNT &optional KILLP This command deletes COUNT characters directly after point, or before point if COUNT is negative. If KILLP is non-`nil', then it saves the deleted characters in the kill ring. In an interactive call, COUNT is the numeric prefix argument, and KILLP is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring. The value returned is always `nil'. - Command: delete-backward-char COUNT &optional KILLP This command deletes COUNT characters directly before point, or after point if COUNT is negative. If KILLP is non-`nil', then it saves the deleted characters in the kill ring. In an interactive call, COUNT is the numeric prefix argument, and KILLP is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring. The value returned is always `nil'. - Command: backward-delete-char-untabify COUNT &optional KILLP This command deletes COUNT characters backward, changing tabs into spaces. When the next character to be deleted is a tab, it is first replaced with the proper number of spaces to preserve alignment and then one of those spaces is deleted instead of the tab. If KILLP is non-`nil', then the command saves the deleted characters in the kill ring. Conversion of tabs to spaces happens only if COUNT is positive. If it is negative, exactly -COUNT characters after point are deleted. In an interactive call, COUNT is the numeric prefix argument, and KILLP is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring. The value returned is always `nil'.  File: elisp, Node: User-Level Deletion, Next: The Kill Ring, Prev: Deletion, Up: Text User-Level Deletion Commands ============================ This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs. - Command: delete-horizontal-space This function deletes all spaces and tabs around point. It returns `nil'. In the following examples, we call `delete-horizontal-space' four times, once on each line, with point between the second and third characters on the successive line. ---------- Buffer: foo ---------- I -!-thought I -!- thought We-!- thought Yo-!-u thought ---------- Buffer: foo ---------- (delete-horizontal-space) ; Four times. => nil ---------- Buffer: foo ---------- Ithought Ithought Wethought You thought ---------- Buffer: foo ---------- - Command: delete-indentation &optional JOIN-FOLLOWING-P This function joins the line point is on to the previous line, deleting any whitespace at the join and in some cases replacing it with one space. If JOIN-FOLLOWING-P is non-`nil', `delete-indentation' joins this line to the following line instead. The value is `nil'. If there is a fill prefix, and the second of the lines being joined starts with the prefix, then `delete-indentation' deletes the fill prefix before joining the lines. In the example below, point is located on the line starting `events', and it makes no difference if there are trailing spaces in the preceding line. ---------- Buffer: foo ---------- When in the course of human -!- events, it becomes necessary ---------- Buffer: foo ---------- (delete-indentation) => nil ---------- Buffer: foo ---------- When in the course of human-!- events, it becomes necessary ---------- Buffer: foo ---------- After the lines are joined, the function `fixup-whitespace' is responsible for deciding whether to leave a space at the junction. - Function: fixup-whitespace This function replaces all the white space surrounding point with either one space or no space, according to the context. It returns `nil'. At the beginning or end of a line, the appropriate amount of space is none. Before a character with close parenthesis syntax, or after a character with open parenthesis or expression-prefix syntax, no space is also appropriate. Otherwise, one space is appropriate. *Note Syntax Class Table::. In the example below, `fixup-whitespace' is called the first time with point before the word `spaces' in the first line. for the second invocation, Point is directly after the `('. ---------- Buffer: foo ---------- This has too many -!-spaces This has too many spaces at the start of (-!- this list) ---------- Buffer: foo ---------- (fixup-whitespace) => nil (fixup-whitespace) => nil ---------- Buffer: foo ---------- This has too many spaces This has too many spaces at the start of (this list) ---------- Buffer: foo ---------- - Command: just-one-space This command replaces any spaces and tabs around point with a single space. It returns `nil'. - Command: delete-blank-lines This function deletes blank lines surrounding point. If point is on a blank line with one or more blank lines before or after it, then all but one of them are deleted. If point is on an isolated blank line, then it is deleted. If point is on a nonblank line, the command deletes all blank lines following it. A blank line is defined as a line containing only tabs and spaces. `delete-blank-lines' returns `nil'.  File: elisp, Node: The Kill Ring, Next: Undo, Prev: User-Level Deletion, Up: Text The Kill Ring ============= "Kill" functions delete text like the deletion functions, but save it so that the user can reinsert it by "yanking". Most of these functions have `kill-' in their name. By contrast, the functions whose names start with `delete-' normally do not save text for yanking (though they can still be undone); these are "deletion" functions. Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. You can use these functions to write commands for killing text. When you need to deleting text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. *Note Deletion::. Killed text is saved for later yanking in the "kill ring". This is a list which holds, not just the last text kill, but a number of recent kills. We call this a "ring" because yanking treats it as a cyclic order. The list is kept in the variable `kill-ring', and can be operated on with the usual functions for lists; there are also specialized functions, described in this section, which treat it as a ring. Some people think this use of the word "kill" is unfortunate, since it refers to operations which specifically *do not* destroy the entities "killed". This is in sharp contrast to ordinary life, in which death is permanent and "killed" entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term "cut ring" makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now. * Menu: * Kill Ring Concepts:: What text looks like in the kill ring. * Kill Functions:: Functions that kill text. * Yank Commands:: Commands that access the kill ring. * Low Level Kill Ring:: Functions and variables for kill ring access. * Internals of Kill Ring:: Variables that hold kill-ring data.  File: elisp, Node: Kill Ring Concepts, Next: Kill Functions, Up: The Kill Ring Kill Ring Concepts ------------------ The kill ring records killed text as strings in a list, most recent first. A short kill ring, for example, might look like this: ("some text" "a different piece of text" "even older text") When the list reaches `kill-ring-max' entries in length, adding a new entry automatically deletes the last entry. When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single entry in the kill ring, which would be yanked as a unit. The second and subsequent consecutive kill commands add text to the entry made by the first one. For yanking, one entry in the kill ring is designated the "front" of the ring. Some yank commands "rotate" the ring by designating a different element as the "front." But this virtual rotation doesn't change the list itself--the most recent entry always comes first in the list.  File: elisp, Node: Kill Functions, Next: Yank Commands, Prev: Kill Ring Concepts, Up: The Kill Ring Functions for Killing --------------------- `kill-region' is the usual subroutine for killing text. Any command that calls this function is a "kill command" (and should probably have `kill' in its name). `kill-region' puts the newly killed text in a new element at the beginning of the kill ring or adds it to the most recent element. It uses the `last-command' variable to determine whether the previous was a kill command, and if so appends the killed text to the most recent entry. - Command: kill-region START END This function kills the text in the region defined by START and END. The text is deleted but saved in the kill ring. The value is always `nil'. In an interactive call, START and END are point and the mark. If the buffer is read-only, `kill-region' modifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use all the kill commands to copy text into the kill ring from a read-only buffer. - Command: copy-region-as-kill START END This command saves the region defined by START and END on the kill ring, but does not delete the text from the buffer. It returns `nil'. It also indicates the extent of the text copied by moving the cursor momentarily, or by displaying a message in the echo area. Don't call `copy-region-as-kill' in Lisp programs unless you aim to support Emacs 18. For Emacs 19, it is better to use `kill-new' or `kill-append' instead. *Note Low Level Kill Ring::.  File: elisp, Node: Yank Commands, Next: Low Level Kill Ring, Prev: Kill Functions, Up: The Kill Ring Functions for Yanking --------------------- "Yanking" means reinserting an entry of previously killed text from the kill ring. - Command: yank &optional ARG This command inserts before point the text in the first entry in the kill ring. It positions the mark at the beginning of that text, and point at the end. If ARG is a list (which occurs interactively when the user types `C-u' with no digits), then `yank' inserts the text as described above, but puts point before the yanked text and puts the mark after it. If ARG is a number, then `yank' inserts the ARGth most recently killed text--the ARGth element of the kill ring list. `yank' does not alter the contents of the kill ring or rotate it. It returns `nil'. - Command: yank-pop ARG This command replaces the just-yanked entry from the kill ring with a different entry from the kill ring. This is allowed only immediately after a `yank' or another `yank-pop'. At such a time, the region contains text that was just inserted by yanking. `yank-pop' deletes that text and inserts in its place a different piece of killed text. It does not add the deleted text to the kill ring, since it is already in the kill ring somewhere. If ARG is `nil', then the replacement text is the previous element of the kill ring. If ARG is numeric, the replacement is the ARGth previous kill. If ARG is negative, a more recent kill is the replacement. The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest. The value is always `nil'.  File: elisp, Node: Low Level Kill Ring, Next: Internals of Kill Ring, Prev: Yank Commands, Up: The Kill Ring Low Level Kill Ring ------------------- These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs. They take care of interaction with X Window selections. They do not exist in Emacs version 18. - Function: current-kill N &optional DO-NOT-MOVE The function `current-kill' rotates the yanking pointer in the kill ring by N places, and returns the text at that place in the ring. If the optional second argument DO-NOT-MOVE is non-`nil', then `current-kill' doesn't alter the yanking pointer; it just returns the Nth kill forward from the current yanking pointer. If N is zero, indicating a request for the latest kill, `current-kill' calls the value of `interprogram-paste-function' (documented below) before consulting the kill ring. - Function: kill-new STRING This function puts the text STRING into the kill ring as a new entry at the front of the ring. It discards the oldest entry if appropriate. It also invokes the value of `interprogram-cut-function' (see below). - Function: kill-append STRING BEFORE-P This function appends the text STRING to the first entry in the kill ring. Normally STRING goes at the end of the entry, but if BEFORE-P is non-`nil', it goes at the beginning. This function also invokes the value of `interprogram-cut-function' (see below). - Variable: interprogram-paste-function This variable provides a way of transferring killed text from other programs, when you are using a window system. Its value should be `nil' or a function of no arguments. If the value is a function, `current-kill' calls it to get the "most recent kill". If the function returns a non-`nil' value, then that value is used as the "most recent kill". If it returns `nil', then the first element of `kill-ring' is used. The normal use of this hook is to get the X server's primary selection as the most recent kill, even if the selection belongs to another X client. *Note X Selections::. - Variable: interprogram-cut-function This variable provides a way of communicating killed text to and from other programs, when you are using a window system. Its value should be `nil' or a function of one argument. If the value is a function, `kill-new' and `kill-append' call it with the new first element of the kill ring as an argument. The normal use of this hook is to set the X server's primary selection to the newly killed text.  File: elisp, Node: Internals of Kill Ring, Prev: Low Level Kill Ring, Up: The Kill Ring Internals of the Kill Ring -------------------------- The variable `kill-ring' holds the kill ring contents, in the form of a list of strings. The most recent kill is always at the front of the list. The `kill-ring-yank-pointer' variable points to a link in the kill ring list, whose CAR is the text to yank next. Moving `kill-ring-yank-pointer' to a different link is called "rotating the kill ring"; we say it identifies the "front" of the ring. We call the kill ring a "ring" because the functions that move the yank pointer wrap around from the end of the list to the beginning, or vice-versa. Rotation of the kill ring is virtual; it does not change the value of `kill-ring'. Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables whose values are normally lists. The word "pointer" in the name of the `kill-ring-yank-pointer' indicates that the variable's purpose is to identify one element of the list for use by the next yank command. The value of `kill-ring-yank-pointer' is always `eq' to one of the links in the kill ring list. The element it identifies is the CAR of that link. Kill commands, which change the kill ring, also set this variable from `kill-ring'. The effect is to rotate the ring so that the newly killed text is at front. Here is a diagram that shows the variable `kill-ring-yank-pointer' pointing to the second entry in the kill ring `("some text" "a different piece of text" "yet older text")'. kill-ring kill-ring-yank-pointer | | | ___ ___ ---> ___ ___ ___ ___ --> |___|___|------> |___|___|--> |___|___|--> nil | | | | | | | | -->"yet older text" | | | --> "a different piece of text" | --> "some text" This state of affairs might occur after `C-y' (`yank') immediately followed by `M-y' (`yank-pop'). - Variable: kill-ring This variable holds list of killed text sequences, most recently killed first. - Variable: kill-ring-yank-pointer This variable's value indicates which element of the kill ring is at the "front" of the ring for yanking. More precisely, the value is a tail of the value of `kill-ring', and its CAR is the kill string that `C-y' should yank. - User Option: kill-ring-max The value of this variable is the maximum length to which the kill ring can grow, before elements are thrown away at the end. The default value for `kill-ring-max' is 30.  File: elisp, Node: Undo, Next: Maintaining Undo, Prev: The Kill Ring, Up: Text Undo ==== Most buffers have an "undo list" which records all changes made to the buffer's text so that they can be undone. (The buffers which don't have one are usually special-purpose buffers for which Emacs assumes that undoing is not useful.) All the primitives which modify the text in the buffer automatically add elements to the front of the undo list, which is in the variable `buffer-undo-list'. - Variable: buffer-undo-list This variable's value is the undo list of the current buffer. A value of `t' disables the recording of undo information. Here are the kinds of elements an undo list can have: `INTEGER' This kind of element records a previous value of point. Ordinary cursor motion does not get any sort of undo record, but deletion commands use these entries to record where point was before the command. `(BEG . END)' This kind of element indicates how to delete text that was inserted. Upon insertion, the text occupied the range BEG-END in the buffer. `(POS . DELETED)' This kind of element indicates how to reinsert text that was deleted. The deleted text itself is the string DELETED. The place to reinsert it is POS. `(t HIGH . LOW)' This kind of element indicates that an unmodified buffer became modified. The elements HIGH and LOW are two integers, each recording 16 bits of the visited file's modification time as of when it was previously visited or saved. `primitive-undo' uses those values to determine whether to mark the buffer as unmodified once again; it does so only if the file's modification time matches those numbers. `(nil PROPERTY VALUE BEG . END)' This kind of element records a change in a text property. Here's how you might undo the change: (put-text-property BEG END PROPERTY VALUE) `nil' This element is a boundary. The elements between two boundaries are called a "change group"; normally, each change group corresponds to one keyboard command, and undo commands normally undo an entire group as a unit. - Function: undo-boundary This function places a boundary element in the undo list. The undo command stops at such a boundary, and successive undo commands undo to earlier and earlier boundaries. This function returns `nil'. The editor command loop automatically creates an undo boundary between keystroke commands. Thus, each undo normally undoes the effects of one command. Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example, `query-replace' calls this function after each replacement so that the user can undo individual replacements one by one. - Function: primitive-undo COUNT LIST This is the basic function for undoing elements of an undo list. It undoes the first COUNT elements of LIST, returning the rest of LIST. You could write this function in Lisp, but it is convenient to have it in C. `primitive-undo' adds elements to the buffer's undo list when it changes the buffer. Undo commands avoid confusion by saving the undo list value at the beginning of a sequence of undo operations. Then the undo operations use and update the saved value. The new elements added by undoing are not part of the saved value, so they don't interfere with continuing to undo.  File: elisp, Node: Maintaining Undo, Next: Filling, Prev: Undo, Up: Text Maintaining Undo Lists ====================== This section describes how to enable and disable undo information for a given buffer. It also explains how the undo list is truncated automatically so it doesn't get too big. Recording of undo information in a newly created buffer is normally enabled to start with; but if the buffer name starts with a space, the undo recording is initially disabled. You can explicitly enable or disable undo recording with the following two functions, or by setting `buffer-undo-list' yourself. - Command: buffer-enable-undo &optional BUFFER-OR-NAME This command enables recording undo information for buffer BUFFER-OR-NAME, so that subsequent changes can be undone. If no argument is supplied, then the current buffer is used. This function does nothing if undo recording is already enabled in the buffer. It returns `nil'. In an interactive call, BUFFER-OR-NAME is the current buffer. You cannot specify any other buffer. - Function: buffer-disable-undo &optional BUFFER - Function: buffer-flush-undo &optional BUFFER This function discards the undo list of BUFFER, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of BUFFER is already disabled, this function has no effect. This function returns `nil'. It cannot be called interactively. The name `buffer-flush-undo' is not considered obsolete, but the preferred name `buffer-disable-undo' is new as of Emacs versions 19. As editing continues, undo lists get longer and longer. To prevent them from using up all available memory space, garbage collection trims them back to size limits you can set. (For this purpose, the "size" of an undo list measures the cons cells that make up the list, plus the strings of deleted text.) Two variables control the range of acceptable sizes: `undo-limit' and `undo-strong-limit'. - Variable: undo-limit This is the soft limit for the acceptable size of an undo list. The change group at which this size is exceeded is the last one kept. - Variable: undo-strong-limit The upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all subsequent changes). There is one exception: garbage collection always keeps the very latest change group no matter how big it is.