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This is Info file elisp, produced by Makeinfo-1.47 from the 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: Text Lines, Next: Screen Lines, Prev: Buffer End Motion, Up: Motion
Motion by Text Lines
--------------------
Text lines are portions of the buffer delimited by newline
characters, which are regarded as part of the previous line. The first
text line begins at the beginning of the buffer, and the last text line
ends at the end of the buffer whether or not the last character is a
newline. The division of the buffer into text lines is not affected by
the width of the window, or by how tabs and control characters are
displayed.
-- Command: goto-line LINE
This function moves point to the front of the LINEth line,
counting from line 1 at beginning of buffer. If LINE is less than
1, then point is set to the beginning of the buffer. If LINE is
greater than the number of lines in the buffer, then point is set
to the *end of the last line* of the buffer.
If narrowing is in effect, then LINE still counts from the
beginning of the buffer, but point cannot go outside the accessible
portion. So point is set at the beginning or end of the accessible
portion of the text if the line number specifies a position that is
inaccessible.
The return value of `goto-line' is the difference between LINE and
the line number of the line to which point actually was able move
(before taking account of any narrowing). Thus, the value is
positive if the scan encounters the end of the buffer.
In an interactive call, LINE is the numeric prefix argument if one
has been provided. Otherwise LINE is read in the minibuffer.
-- Command: beginning-of-line &optional COUNT
This function moves point to the beginning of the current line.
With an argument COUNT not `nil' or 1, it moves forward COUNT-1
lines and then to the beginning of the line.
If this function reaches the end of the buffer (or of the
accessible portion, if narrowing is in effect), it positions point
at the beginning of the last line. No error is signaled.
-- Command: end-of-line &optional COUNT
This function moves point to the end of the current line. With an
argument COUNT not `nil' or 1, it moves forward COUNT-1 lines and
then to the end of the line.
If this function reaches the end of the buffer (or of the
accessible portion, if narrowing is in effect), it positions point
at the end of the last line. No error is signaled.
-- Command: forward-line &optional COUNT
This function moves point forward COUNT lines, to the beginning of
the line. If COUNT is negative, it moves point -COUNT lines
backward, to the beginning of the line.
If the beginning or end of the buffer (or of the accessible
portion) is encountered before that many lines are found, then
point stops at the beginning or end. No error is signaled.
`forward-line' returns the difference between COUNT and the number
of lines actually moved. If you attempt to move down five lines
from the beginning of a buffer that has only three lines, point
will positioned at the end of the last line, and the value will be
2.
In an interactive call, COUNT is the numeric prefix argument.
-- Function: count-lines START END
This function returns the number of lines between the positions
START and END in the current buffer. If START and END are equal,
then it returns 0. Otherwise it returns at least 1, even if START
and END are on the same line. This is because the text between
them, considered in isolation, must contain at least one line
unless it is empty.
Here is an example of using `count-lines':
(defun current-line ()
"Return the vertical position of point in the selected window.
Top line is 0. Counts each text line only once, even if it wraps."
(+ (count-lines (window-start) (point))
(if (= (current-column) 0) 1 0)
-1))
Also see the functions `bolp' and `eolp' in *Note Near Point::.
These functions do not move point, but test whether it is already at the
beginning or end of a line.
File: elisp, Node: Screen Lines, Next: Vertical Motion, Prev: Text Lines, Up: Motion
Motion by Screen Lines
----------------------
The line functions in the previous section count text lines,
delimited only by newline characters. By contrast, these functions
count screen lines, which are defined by the way the text appears on
the screen. A text line is a single screen line if it is short enough
to fit the width of the selected window, but otherwise it may occupy
several screen lines.
In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines. Then `vertical-motion' moves
point just like `forward-line'. *Note Truncation::.
Because the width of a given string depends on the flags which
control the appearance of certain characters, `vertical-motion' will
behave differently on a given piece of text found in different buffers.
It will even act differently in different windows showing the same
buffer, because the width may differ and so may the truncation flag.
*Note Control Char Display::.
-- Function: vertical-motion COUNT
This function moves point to the start of the screen line COUNT
screen lines down from the screen line containing point. If COUNT
is negative, it moves up instead.
This function returns the number of lines moved. The value may be
less in absolute value than COUNT if the beginning or end of the
buffer was reached.
-- Command: move-to-window-line COUNT
This function moves point with respect to the text currently
displayed in the selected window. Point is moved to the beginning
of the screen line COUNT screen lines from the top of the window.
If COUNT is negative, point moves either to the beginning of the
line -COUNT lines from the bottom or else to the last line of the
buffer if the buffer ends above the specified screen position.
If COUNT is `nil', then point moves to the beginning of the line
in the middle of the window. If the absolute value of COUNT is
greater than the size of the window, then point moves to the place
which would appear on that screen line if the window were tall
enough. This will probably cause the next redisplay to scroll to
bring that location onto the screen.
In an interactive call, COUNT is the numeric prefix argument.
The value returned is the window line number, with the top line in
the window numbered 0.
File: elisp, Node: Vertical Motion, Next: List Motion, Prev: Screen Lines, Up: Motion
The User-Level Vertical Motion Commands
---------------------------------------
A goal column is useful if you want to edit text such as a table in
which you want to move point to a certain column on each line. The goal
column affects the vertical text line motion commands, `next-line' and
`previous-line'. *Note Basic Editing Commands: (emacs)Basic.
-- User Option: goal-column
This variable holds an explicitly specified goal column for
vertical line motion commands. If it is an integer, it specifies
a column, and these commands try to move to that column on each
line. If it is `nil', then the commands set their own goal
columns. Any other value is invalid.
-- Variable: temporary-goal-column
This variable holds the temporary goal column during a sequence of
consecutive vertical line motion commands. It is overridden by
`goal-column' if that is non-`nil'. It is set each time a
vertical motion command is invoked, unless the previous command
was also a vertical motion command.
-- User Option: track-eol
This variable controls how the vertical line motion commands
operate when starting at the end of a line. If `track-eol' is
non-`nil', then vertical motion starting at the end of a line will
keep to the ends of lines. This means moving to the end of each
line moved onto. The value of `track-eol' has no effect if point
is not at the end of a line when the first vertical motion command
is given.
`track-eol' has its effect by causing `temporary-goal-column' to
be set to 9999 instead of to the current column.
-- Command: set-goal-column UNSET
This command sets the variable `goal-column' to specify a permanent
goal column for the vertical line motion commands. If UNSET is
`nil', then `goal-column' is set to the current column of point.
If UNSET is non-`nil', then `goal-column' is set to `nil'.
This function is intended for interactive use; and in an
interactive call, UNSET is the raw prefix argument.
File: elisp, Node: List Motion, Next: Skipping Characters, Prev: Vertical Motion, Up: Motion
Moving over Lists and Other Balanced Expressions
------------------------------------------------
Here are several functions concerned with balanced-parenthesis
expressions (also called "sexps" in connection with moving across them
in Emacs). The syntax table controls how these functions interpret
various characters; see *Note Syntax Tables::. *Note Parsing
Expressions::, for lower-level primitives for scanning sexps or parts of
sexps. For user-level commands, see *Note Lists and Sexps:
(emacs)Lists and Sexps.
-- Command: forward-list ARG
Move forward across ARG balanced groups of parentheses. (Other
syntatic entities such as words or paired string quotes are
ignored.)
-- Command: backward-list ARG
Move backward across ARG balanced groups of parentheses. (Other
syntatic entities such as words or paired string quotes are
ignored.)
-- Command: up-list ARG
Move forward out of ARG levels of parentheses. A negative argument
means move backward but still to a less deep spot.
-- Command: down-list ARG
Move forward down ARG levels of parentheses. A negative argument
means move backward but still go down ARG level.
-- Command: forward-sexp ARG
Move forward across ARG balanced expressions. Balanced expressions
include both those delimited by parentheses and other kinds, such
as words and string constants. For example,
---------- Buffer: foo ----------
(concat-!- "foo " (car x) y z)
---------- Buffer: foo ----------
(forward-sexp 3)
=> nil
---------- Buffer: foo ----------
(concat "foo " (car x) y-!- z)
---------- Buffer: foo ----------
-- Command: backward-sexp ARG
Move backward across ARG balanced expressions.
File: elisp, Node: Skipping Characters, Prev: List Motion, Up: Motion
Skipping Characters
-------------------
The following two functions move point over a specified set of
characters. For example, they are often used to skip whitespace.
-- Function: skip-chars-forward CHARACTER-SET &optional LIMIT
This function moves point in the current buffer forward, skipping
over a given set of characters. Emacs first examines the
character following point; if it matches CHARACTER-SET, then point
is advanced and the next character is examined. This continues
until a character is found that does not match. The function
returns `nil'.
The argument CHARACTER-SET is like the inside of a `[...]' in a
regular expression except that `]' is never special and `\' quotes
`^', `-' or `\'. Thus, `"a-zA-Z"' skips over all letters,
stopping before the first nonletter, and `"^a-zA-Z'" skips
nonletters stopping before the first letter. *Note Regular
Expressions::.
If LIMIT is supplied (it must be a number or a marker), it
specifies the maximum position in the buffer that point can be
skipped to. Point will stop at or before LIMIT.
In the following example, point is initially located directly
before the `T'. After the form is evaluated, point is located at
the end of that line (between the `t' of `hat' and the newline).
The function skips all letters and spaces, but not newlines.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(skip-chars-forward "a-zA-Z ")
=> nil
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
-- Function: skip-chars-backward CHARACTER-SET &optional LIMIT
This function moves point backward, skipping characters that match
CHARACTER-SET. It just like `skip-chars-forward' except for the
direction of motion.
File: elisp, Node: Excursions, Next: Narrowing, Prev: Motion, Up: Positions
Excursions
==========
It is often useful to move point "temporarily" within a localized
portion of the program, or to switch buffers temporarily. This is
called an "excursion", and it is done with the `save-excursion' special
form. This construct saves the current buffer and its values of point
and the mark so they can be restored after the completion of the
excursion.
The forms for saving and restoring the configuration of windows are
described elsewhere (*note Window Configurations::.).
-- Special Form: save-excursion FORMS...
The `save-excursion' special form saves the identity of the current
buffer and the values of point and the mark in it, evaluates FORMS,
and finally restores the buffer and its saved values of point and
the mark. All three saved values are restored even in case of an
abnormal exit via throw or error (*note Nonlocal Exits::.).
The `save-excursion' special form is the standard way to switch
buffers or move point within one part of a program and avoid
affecting the rest of the program. It is used more than 500 times
in the Lisp sources of Emacs.
The values of point and the mark for other buffers are not saved by
`save-excursion', so any changes made to point and the mark in the
other buffers will remain in effect after `save-excursion' exits.
Likewise, `save-excursion' does not restore window-buffer
correspondences altered by functions such as `switch-to-buffer'.
One way to restore these correspondences, and the selected window,
is to use `save-window-excursion' inside `save-excursion' (*note
Window Configurations::.).
The value returned by `save-excursion' is the result of the last of
FORMS, or `nil' if no FORMS are given.
(save-excursion
FORMS)
==
(let ((old-buf (current-buffer))
(old-pnt (point-marker))
(old-mark (copy-marker (mark-marker))))
(unwind-protect
(progn FORMS)
(set-buffer old-buf)
(goto-char old-pnt)
(set-marker (mark-marker) old-mark)))
File: elisp, Node: Narrowing, Prev: Excursions, Up: Positions
Narrowing
=========
"Narrowing" means limiting the text addressable by Emacs editing
commands to a limited range of characters in a buffer. The text that
remains addressable is called the "accessible portion" of the buffer.
Narrowing is specified with two buffer positions which become the
beginning and end of the accessible portion. For most editing commands
these positions replace the values of the beginning and end of the
buffer. While narrowing is in effect, no text outside the accessible
portion is displayed, and point cannot move outside the accessible
portion.
Values such as positions or line numbers which usually count from the
beginning of the buffer continue to do so, but the functions which use
them will refuse to operate on text that is inaccessible.
The commands for saving buffers are unaffected by narrowing; the
entire buffer is saved regardless of the any narrowing.
-- Command: narrow-to-region START END
This function sets the accessible portion of the current buffer to
start at START and end at END. Both arguments should be character
positions.
In an interactive call, START and END are set to the bounds of the
current region (point and the mark, with the smallest first).
-- Command: narrow-to-page MOVE-COUNT
This function sets the accessible portion of the current buffer to
include just the current page. An optional first argument
MOVE-COUNT non-`nil' means to move forward or backward by
MOVE-COUNT pages and then narrow.
In an interactive call, MOVE-COUNT is set to the numeric prefix
argument.
-- Command: widen
This function cancels any narrowing in the current buffer, so that
the entire contents are accessible. This is called "widening". It
is equivalent to the following expression:
(narrow-to-region 1 (1+ (buffer-size)))
-- Special Form: save-restriction FORMS...
This special form saves the current bounds of the accessible
portion, evaluates FORMS, and finally restores the saved bounds,
thus restoring the same state of narrowing (or absence thereof)
formerly in effect. The state of narrowing is restored even in
the event of an abnormal exit via throw or error (*note Nonlocal
Exits::.). Therefore, this construct is a clean way to narrow a
buffer temporarily.
The value returned by `save-restriction' is that returned by the
last of FORMS, or `nil' if no forms were given.
*Note:* it is easy to make a mistake when using
`save-restriction'. Read the entire description here before you
try it.
Point and the mark are *not* restored by this special form; use
`save-excursion' for that. If you use both `save-restriction' and
`save-excursion' together, `save-excursion' should come first (on
the outside). Otherwise, the old point value would be restored
with temporary narrowing still in effect. If the old point value
were outside the limits of the temporary narrowing, this would
fail to restore it accurately.
The `save-restriction' special form records the values of the
beginning and end of the accessible portion as distances from the
beginning and end of the buffer. In other words, it records the
amount of inaccessible text before and after the accessible
portion.
This technique yields correct results if the body of the form does
further narrowing. However, `save-restriction' can become confused
if the body widens and then makes changes outside the area of the
saved narrowing. When this is what you want to do,
`save-restriction' is not the right tool for the job. Here is
what you must do instead:
(let ((beg (point-min-marker))
(end (point-max-marker)))
(unwind-protect
(progn BODY)
(narrow-to-region beg end)))
Here is a simple example of correct use of `save-restriction':
---------- Buffer: foo ----------
This is the contents of foo
This is the contents of foo
This is the contents of foo-!-
---------- Buffer: foo ----------
(save-excursion
(save-restriction
(goto-char 1)
(forward-line 2)
(narrow-to-region 1 (point))
(goto-char (point-min))
(replace-string "foo" "bar")))
---------- Buffer: foo ----------
This is the contents of bar
This is the contents of bar
This is the contents of foo-!-
---------- Buffer: foo ----------
File: elisp, Node: Markers, Next: Text, Prev: Positions, Up: Top
Markers
*******
A "marker" is a Lisp object used to specify a position in a buffer
relative to the surrounding text. A marker changes its offset from the
beginning of the buffer automatically whenever text is inserted or
deleted, so that it stays with the two characters on either side of it.
* Menu:
* Overview of Markers:: The components of a marker, and how it relocates.
* Predicates on Markers:: Testing whether an object is a marker.
* Creating Markers:: Making empty markers or markers at certain places.
* Information from Markers:: Finding the marker's buffer or character position.
* Changing Markers:: Moving the marker to a new buffer or position.
* The Mark:: How "the mark" is implemented with a marker.
* The Region:: How to access "the region".
File: elisp, Node: Overview of Markers, Next: Predicates on Markers, Prev: Markers, Up: Markers
Overview of Markers
===================
A marker specifies a buffer and a position in that buffer. The
marker can be used to represent a position in the functions that
require one, just as an integer could be used. *Note Positions::, for
a complete description of positions.
A marker has two attributes: the marker position, and the marker
buffer. The marker position is an integer which is equivalent (at the
moment) to the marker as a position in that buffer; however, as text is
inserted or deleted in the buffer, the marker is relocated, so that its
integer equivalent changes. The idea is that a marker positioned
between two characters in a buffer will remain between those two
characters despite any changes made to the contents of the buffer; thus,
a marker's offset from the beginning of a buffer may change often during
the life of the marker.
If the text around a marker is deleted, the marker is repositioned
between the characters immediately before and after the deleted text.
If text is inserted at the position of a marker, the marker remains in
front of the new text unless it is inserted with `insert-before-markers'
(*note Insertion::.). When text is inserted or deleted somewhere
before the marker position (not next to the marker), the marker moves
back and forth with the two neighboring characters.
When a buffer is modified, all of its markers must be checked so that
they can be relocated if necessary. This slows processing in a buffer
with a large number of markers. For this reason, it is a good idea to
make a marker point nowhere if you are sure you don't need it any more.
Unreferenced markers will eventually be garbage collected, but until
then will continue to be updated if they do point somewhere.
Because it is quite common to perform arithmetic operations on a
marker position, most of the arithmetic operations (including `+' and
`-') accept markers as arguments. In such cases, the current position
of the marker is used.
Here are examples of creating markers, setting markers, and moving
point to markers:
;; Make a new marker that initially does not point anywhere:
(setq m1 (make-marker))
=> #<marker in no buffer>
;; Set `m1' to point between the 100th and 101st characters.
;; in the current buffer:
(set-marker m1 100)
=> #<marker at 100 in markers.texi>
;; Now insert one character at the beginning of the buffer:
(goto-char (point-min))
=> 1
(insert "Q")
=> nil
;; `m1' is updated appropriately.
m1
=> #<marker at 101 in markers.texi>
;; Two markers that point to the same position
;; are not `eq', but they are `equal'.
(setq m2 (copy-marker m1))
=> #<marker at 101 in markers.texi>
(eq m1 m2)
=> nil
(equal m1 m2)
=> t
;; When you are finished using a marker, make it point nowhere.
(set-marker m1 nil)
=> #<marker in no buffer>
File: elisp, Node: Predicates on Markers, Next: Creating Markers, Prev: Overview of Markers, Up: Markers
Predicates on Markers
=====================
You can test an object to see whether it is a marker, or whether it
is either an integer or a marker. The latter test is useful when you
are using the arithmetic functions that work with both markers and
integers.
-- Function: markerp OBJECT
This function returns `t' if OBJECT is a marker, `nil' otherwise.
In particular, integers are not markers, even though many
functions will accept either a marker or an integer.
-- Function: integer-or-marker-p OBJECT
This function returns `t' if OBJECT is an integer or a marker,
`nil' otherwise.
File: elisp, Node: Creating Markers, Next: Information from Markers, Prev: Predicates on Markers, Up: Markers
Functions That Create Markers
=============================
When you create a new marker, you can make it point nowhere, or point
to the present position of point, or to the beginning or end of the
accessible portion of the buffer, or to the same place as another given
marker.
-- Function: make-marker
This functions returns a newly allocated marker that does not point
anywhere.
(make-marker)
=> #<marker in no buffer>
-- Function: point-marker
This function returns a new marker that points to the present
position of point in the current buffer. *Note Point::. For an
example, see `copy-marker', below.
-- Function: point-min-marker
This function returns a new marker that points to the beginning of
the accessible portion of the buffer. This will be the beginning
of the buffer unless narrowing is in effect. *Note Narrowing::.
-- Function: point-max-marker
This function returns a new marker that points to the end of the
accessible portion of the buffer. This will be the end of the
buffer unless narrowing is in effect. *Note Narrowing::.
Here are examples of this function and `point-min-marker', shown in
a buffer containing a version of the source file for the text of
this chapter.
(point-min-marker)
=> #<marker at 1 in markers.texi>
(point-max-marker)
=> #<marker at 15573 in markers.texi>
(narrow-to-region 100 200)
=> nil
(point-min-marker)
=> #<marker at 100 in markers.texi>
(point-max-marker)
=> #<marker at 200 in markers.texi>
-- Function: copy-marker MARKER-OR-INTEGER
If passed a marker as its argument, `copy-marker' returns a new
marker that points to the same place and the same buffer as does
MARKER-OR-INTEGER. If passed an integer as its argument,
`copy-marker' returns a new marker that points to position
MARKER-OR-INTEGER in the current buffer.
If passed an argument that is an integer whose value is less than
1, `copy-marker' returns a new marker that points to the beginning
of the current buffer. If passed an argument that is an integer
whose value is greater than the length of the buffer, then
`copy-marker' returns a new marker that points to the end of the
buffer.
An error is signaled if MARKER is neither a marker nor an integer.
(setq p (point-marker))
=> #<marker at 2139 in markers.texi>
(setq q (copy-marker p))
=> #<marker at 2139 in markers.texi>
(eq p q)
=> nil
(equal p q)
=> t
(copy-marker 0)
=> #<marker at 1 in markers.texi>
(copy-marker 20000)
=> #<marker at 7572 in markers.texi>
File: elisp, Node: Information from Markers, Next: Changing Markers, Prev: Creating Markers, Up: Markers
Information from Markers
========================
This section describes the functions for accessing the components of
a marker object.
-- Function: marker-position MARKER
This function returns the position that MARKER points to, or `nil'
if it points nowhere.
-- Function: marker-buffer MARKER
This function returns the buffer that MARKER points into, or `nil'
if it points nowhere.
(setq m (make-marker))
=> #<marker in no buffer>
(marker-position m)
=> nil
(marker-buffer m)
=> nil
(set-marker m 3770 (current-buffer))
=> #<marker at 3770 in markers.texi>
(marker-buffer m)
=> #<buffer markers.texi>
(marker-position m)
=> 3770
Two distinct markers will be found `equal' (even though not `eq') to
each other if they have the same position and buffer, or if they both
point nowhere.
File: elisp, Node: Changing Markers, Next: The Mark, Prev: Information from Markers, Up: Markers
Changing Markers
================
This section describes how to change the position of an existing
marker. When you do this, be sure you know whether the marker is used
outside of your program, and, if so, what effects will result from
moving it--otherwise, confusing things may happen in other parts of
Emacs.
-- Function: set-marker MARKER POSITION &optional BUFFER
This function moves MARKER to POSITION in BUFFER. If BUFFER is
not provided, it defaults to the current buffer.
If POSITION is less than 1, `set-marker' moves marker to the
beginning of the buffer. If the value of POSITION is greater than
the size of the buffer, `set-marker' moves marker to the end of
the buffer. If POSITION is `nil' or a marker that points nowhere,
then MARKER is set to point nowhere.
The value returned is MARKER.
(setq m (point-marker))
=> #<marker at 4714 in markers.texi>
(set-marker m 55)
=> #<marker at 55 in markers.texi>
(setq b (get-buffer "foo"))
=> #<buffer foo>
(set-marker m 0 b)
=> #<marker at 1 in foo>
-- Function: move-marker MARKER POSITION &optional BUFFER
This is another name for `set-marker'.
File: elisp, Node: The Mark, Next: The Region, Prev: Changing Markers, Up: Markers
The Mark
========
A 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 will provide the values of point and
the mark as arguments to the command in an interactive call, but will
permit 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".
In addition to the mark, each buffer has a "mark ring" which is a
list of markers that are the 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 mark ring may contain no more than the
maximum number of entries specified by the variable `mark-ring-max';
excess entries are discarded on a first-in-first-out basis.
-- Function: mark
This function returns the position of the current buffer's mark as
an integer. `nil' is returned if the mark is not yet set for this
buffer.
-- Function: mark-marker
This function returns the current buffer's mark. This 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))
=> #<marker at 3420 in markers.texi>
(set-marker m 100)
=> #<marker at 100 in markers.texi>
(mark-marker)
=> #<marker at 100 in markers.texi>
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, if rather odd, results.
-- Command: set-mark-command JUMP
If JUMP is `nil', this command sets the mark to the value of point
and pushes the previous value of the mark on the mark ring. The
message `Mark set' is also displayed in the echo area.
If JUMP is not `nil', this command sets point to the value of the
mark, and sets the mark to the previous saved mark value, which is
popped off the mark ring.
This function is *only* intended for interactive use.
-- Function: set-mark POSITION
This function sets the mark to POSITION. The old value of the mark
is *not* pushed onto the mark ring.
*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', which is why 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))).
-- 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
=> (#<marker at 11050 in markers.texi>
#<marker at 10832 in markers.texi>
...)
-- 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', it discards
marks on a first-in, first-out basis.
-- Function: push-mark &optional POSITION NOMSG
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'.
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 change
the buffer's point and does nothing if `mark-ring' is empty.
The return value is not useful.
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 instead
use `interactive' with the `r' specification, so that the same function
can be called with explicit bounds arguments from programs. (*Note
Interactive Codes::.)
File: elisp, Node: Text, Next: Searching and Matching, Prev: Markers, Up: Top
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 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)' perform identically. 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.
* 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.
* Auto Filling:: How auto-fill mode is implemented to break lines.
* Filling:: Functions for explicit filling.
* Sorting:: Functions for sorting parts of the buffer.
* Indentation:: Functions to insert or adjust indentation.
* Columns:: Computing horizontal positions, and using them.
* Case Changes:: Case conversion of parts of the buffer.
* Substitution:: Replacing a given character wherever it appears.
* Underlining:: Inserting or deleting underlining-by-overstrike.
* Registers:: How registers are implemented. Accessing the text or
position stored in a register.
File: elisp, Node: Near Point, Next: Buffer Contents, Prev: Text, 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 Searching and Matching::.
-- 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, than the value is `nil'.
Remember that point is always between characters, and the terminal
cursor normally appears over the character following point.
Therefore, the character returned by `char-after' is the character
the cursor is over.
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, point
is at the end of the buffer, then the result of `following-char' is
0.
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, then the result of
`preceding-char' is 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::.
-- Function: eolp
This function returns `t' if point is at the end of a line. The
end of the buffer is always considered the end of a line.
File: elisp, Node: Buffer Contents, Next: Insertion, 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, Emacs 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: Insertion, Next: Commands for Insertion, Prev: Buffer Contents, Up: Text
Insertion
=========
Insertion takes place at point. Markers pointing at positions after
the insertion point are relocated with the surrounding text (*note
Markers::.). When a marker points at the place of insertion, it is
normally not relocated, so that it points to the beginning of the
inserted text; however, when `insert-before-markers' is used, all such
markers are relocated to point after the inserted text.
Point may end up either before or after inserted text, depending on
the function used. If point is left after the inserted text, we speak
of insertion "before point".
Each of these functions signals 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 a
marker whose position initially equals point is relocated to come
after the newly inserted text.
-- Function: insert-char CHARACTER COUNT
This function inserts COUNT instances of CHARACTER into the
current buffer before point. COUNT must be a number, and
CHARACTER must be a character. The value is `nil'.
-- Function: insert-buffer-substring FROM-BUFFER-OR-NAME START END
This function inserts a substring of the contents of buffer
FROM-BUFFER-OR-NAME (which must already exist) into the current
buffer before point. The text inserted consists of the characters
in the region defined by START and END. The value is `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 ----------
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 function 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 unpredictable.
-- Command: quoted-insert COUNT
This function reads the next input character verbatim and inserts
it. It is primarily useful for inserting control characters. You
may also type up to 3 octal digits, to insert a character with
that code.
The argument COUNT is the number of these characters to insert. An
error is signaled if COUNT is not a number.
This function is primarily for interactive use; there is no reason
to use it in a program except for installing it on a keymap. It
returns `nil'.
-- Command: self-insert-command COUNT
This function inserts the last character typed COUNT times and
returns `nil'. This is the function that most printing characters
are bound to. 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-hook' 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 (*note
Abbrevs::.) is enabled and the inserted character does not have
word-constituent syntax (*note Syntax Class Table::.).
This function is also responsible for calling the
`blink-paren-hook' when the inserted character has close
parenthesis syntax (*note Blinking::.).
-- Command: newline &optional NUMBER-OF-NEWLINES
This function 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 function 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.
-- Command: open-line COUNT
This function inserts COUNT newlines into the current buffer after
point, leaving point where it was.
In an interactive call, COUNT is the numeric prefix argument.
Programs hardly ever use this function. The value is
unpredictable.
-- Command: overwrite-mode ARGUMENT
This function turns Overwrite mode on or off. If ARGUMENT is
`nil' then the mode is toggled. Otherwise, if ARGUMENT is a
positive number (greater than zero), then the mode is turned on;
any other argument turns it off.
When Overwrite mode is on, self-inserting graphic characters
replace existing text character for character, and do not push the
existing text to the right.
This function affects primarily `self-insert-command'.
In an interactive call, ARGUMENT is set to the raw prefix
argument. The return value of `overwrite-mode' is unpredictable.
-- Variable: overwrite-mode
Overwrite mode is in effect when this variable is non-`nil'. It is
automatically made buffer-local when set in any fashion.