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Many Emacs commands operate on an arbitrary contiguous part of the current buffer. To specify the text for such a command to operate on, you set the mark at one end of it, and move point to the other end. The text between point and the mark is called the region. Emacs highlights the region whenever there is one, if you enable Transient Mark mode (see section Transient Mark Mode).
Certain Emacs commands set the mark; other editing commands do not affect it, so the mark remains where you set it last. Each Emacs buffer has its own mark, and setting the mark in one buffer has no effect on other buffers' marks. When you return to a buffer that was current earlier, its mark is at the same place as before.
The ends of the region are always point and the mark. It doesn't matter which of them was put in its current place first, or which one comes earlier in the text--the region starts from point or the mark (whichever comes first), and ends at point or the mark (whichever comes last). Every time you move point, or set the mark in a new place, the region changes.
Many commands that insert text, such as C-y (yank) and
M-x insert-buffer, position point and the mark at opposite ends
of the inserted text, so that the region consists of the text just
inserted.
Aside from delimiting the region, the mark is also useful for remembering a spot that you may want to go back to. To make this feature more useful, each buffer remembers 16 previous locations of the mark in the mark ring.
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Here are some commands for setting the mark:
Set the mark where point is (set-mark-command).
The same.
Interchange mark and point (exchange-point-and-mark).
Set point and the mark around the text you drag across.
Set the mark where point is, then move point to where you click
(mouse-save-then-kill).
For example, suppose you wish to convert part of the buffer to
upper case, using the C-x C-u (upcase-region) command,
which operates on the text in the region. You can first go to the
beginning of the text to be capitalized, type C-SPC to put
the mark there, move to the end, and then type C-x C-u. Or, you
can set the mark at the end of the text, move to the beginning, and then
type C-x C-u.
The most common way to set the mark is with the C-SPC command
(set-mark-command). This sets the mark where point is. Then you
can move point away, leaving the mark behind.
There are two ways to set the mark with the mouse. You can drag mouse button one across a range of text; that puts point where you release the mouse button, and sets the mark at the other end of that range. Or you can click mouse button three, which sets the mark at point (like C-SPC) and then moves point where you clicked (like Mouse-1).
Using the mouse to mark a region copies the region into the kill ring in addition to setting the mark; that gives behavior consistent with other window-driven applications. If you don't want to modify the kill ring, you must use keyboard commands to set the mark. See section Mouse Commands for Editing.
When Emacs was developed, terminals had only one cursor, so Emacs does not show where the mark is located-you have to remember. If you enable Transient Mark mode (see below), then the region is highlighted when it is active; you can tell mark is at the other end of the highlighted region. But this only applies when the mark is active.
The usual solution to this problem is to set the mark and then use
it soon, before you forget where it is. Alternatively, you can see
where the mark is with the command C-x C-x
(exchange-point-and-mark) which puts the mark where point was
and point where the mark was. The extent of the region is unchanged,
but the cursor and point are now at the previous position of the mark.
In Transient Mark mode, this command also reactivates the mark.
C-x C-x is also useful when you are satisfied with the position of point but want to move the other end of the region (where the mark is); do C-x C-x to put point at that end of the region, and then move it. Using C-x C-x a second time, if necessary, puts the mark at the new position with point back at its original position.
For more facilities that allow you to go to previously set marks, see The Mark Ring.
There is no such character as C-SPC in ASCII;
when you type SPC while holding down CTRL on a text
terminal, what you get is the character C-@. This key is also
bound to set-mark-command-so unless you are unlucky enough to
have a text terminal where typing C-SPC does not produce
C-@, you might as well think of this character as
C-SPC.
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On a terminal that supports colors, Emacs has the ability to highlight the current region. But normally it does not. Why not?
In the normal mode of use, every command that sets the mark also activates it, and nothing ever deactivates it. Thus, once you have set the mark in a buffer, there is always a region in that buffer. Highlighting the region all the time would be a nuisance. So normally Emacs highlights the region only immediately after you have selected one with the mouse.
If you want region highlighting, you can use Transient Mark mode. This is a more rigid mode of operation in which the region "lasts" only until you use it; operating on the region text deactivates the mark, so there is no region any more. Therefore, you must explicitly set up a region for each command that uses one.
When Transient Mark mode is enabled, Emacs highlights the region, whenever there is a region. In Transient Mark mode, most of the time there is no region; therefore, highlighting the region when it exists is useful and not annoying.
To enable Transient Mark mode, type M-x transient-mark-mode. This command toggles the mode; you can use the same command to turn the mode off again.
Here are the details of Transient Mark mode:
To set the mark, type C-SPC (set-mark-command).
This makes the mark active and thus begins highlighting of the region.
As you move point, you will see the highlighted region grow and
shrink.
The mouse commands for specifying the mark also make it active. So do keyboard commands whose purpose is to specify a region, including M-@, C-M-@, M-h, C-M-h, C-x C-p, and C-x h.
You can tell that the mark is active because the region is highlighted.
When the mark is active, you can execute commands that operate on the region, such as killing, indenting, or writing to a file.
Any change to the buffer, such as inserting or deleting a character, deactivates the mark. This means any subsequent command that operates on a region will get an error and refuse to operate. You can make the region active again by typing C-x C-x.
If Delete Selection mode is also enabled, some commands delete the region when used while the mark is active. See section Mouse Commands for Editing.
Quitting with C-g deactivates the mark.
Commands like M-> and C-s, that "leave the mark behind" in
addition to some other primary purpose, do not activate the new mark.
You can activate the new region by executing C-x C-x
(exchange-point-and-mark).
Commands that normally set the mark before moving long distances (like M-< and C-s) do not alter the mark in Transient Mark mode when the mark is active.
Some commands operate on the region if a region is active. For instance, C-x u in Transient Mark mode operates on the region, when there is a region. (Outside Transient Mark mode, you must type C-u C-x u if you want it to operate on the region.) See section Undo. Other commands that act this way are identified in their own documentation.
The highlighting of the region uses the region face; you can
customize the appearance of the highlighted region by changing this
face. See section Customizing Faces.
When multiple windows show the same buffer, they can have different
regions, because they can have different values of point (though they
all share one common mark position). Ordinarily, only the selected
window highlights its region (see section Multiple Windows). However, if the
variable highlight-nonselected-windows is non-nil, then
each window highlights its own region (provided that Transient Mark mode
is enabled and the mark in the window's buffer is active).
If the variable mark-even-if-inactive is non-nil in
Transient Mark mode, then commands can use the mark and the region
even when it is inactive. Region highlighting appears and disappears
just as it normally does in Transient Mark mode, but the mark doesn't
really go away when the highlighting disappears, so you can still use
region commands.
Transient Mark mode is also sometimes known as "Zmacs mode" because the Zmacs editor on the MIT Lisp Machine handled the mark in a similar way.
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If you don't like Transient Mark mode in general, you might still want to use it once in a while. To do this, type C-SPC C-SPC or C-u C-x C-x. These commands set or activate the mark, and enable Transient Mark mode only until the mark is deactivated.
Set the mark at point (like plain C-SPC), and enable Transient Mark mode just once until the mark is deactivated. (This is not really a separate command; you are using the C-SPC command twice.)
Activate the mark without changing it; enable Transient Mark mode just
once, until the mark is deactivated. (This is the C-x C-x
command, exchange-point-and-mark, with a prefix argument.)
One of the secondary features of Transient Mark mode is that certain commands operate only on the region, when there is an active region. If you don't use Transient Mark mode, the region once set never becomes inactive, so there is no way for these commands to make such a distinction. Enabling Transient Mark mode momentarily gives you a way to use these commands on the region.
Momentary use of Transient Mark mode is also a way to highlight the region for the time being.
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Once you have a region and the mark is active, here are some of the ways you can operate on the region:
Kill it with C-w (see section Killing and Moving Text).
Save it in a register with C-x r s (see section Registers).
Save it in a buffer or a file (see section Accumulating Text).
Convert case with C-x C-l or C-x C-u (see section Case Conversion Commands).
Indent it with C-x TAB or C-M-\ (see section Indentation).
Fill it as text with M-x fill-region (see section Filling Text).
Print hardcopy with M-x print-region (see section Printing Hard Copies).
Evaluate it as Lisp code with M-x eval-region (see section Evaluating Emacs Lisp Expressions).
Undo changes within it using C-u C-x u (see section Undo).
Most commands that operate on the text in the region have the word
region in their names.
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Here are the commands for placing point and the mark around a textual object such as a word, list, paragraph or page.
Set mark after end of next word (mark-word). This command and
the following one do not move point.
Set mark after end of following balanced expression (mark-sexp).
Put region around current paragraph (mark-paragraph).
Put region around current defun (mark-defun).
Put region around the entire buffer (mark-whole-buffer).
Put region around current page (mark-page).
M-@ (mark-word) puts the mark at the end of the next
word, while C-M-@ (mark-sexp) puts it at the end of the
next balanced expression (see section Expressions with Balanced Parentheses). These commands handle
arguments just like M-f and C-M-f. Repeating these
commands extends the region. For example, you can type either
C-u 2 M-@ or M-@ M-@ to mark the next two words. These
commands also extend the region in Transient Mark mode, regardless of
the last command.
Other commands set both point and mark, to delimit an object in the
buffer. For example, M-h (mark-paragraph) moves point to
the beginning of the paragraph that surrounds or follows point, and
puts the mark at the end of that paragraph (see section Paragraphs). It
prepares the region so you can indent, case-convert, or kill a whole
paragraph. With a prefix argument, if the argument's value is positive,
M-h marks that many paragraphs starting with the one surrounding
point. If the prefix argument is -n, M-h also
marks n paragraphs, running back form the one surrounding point.
In that last case, point moves forward to the end of that paragraph,
and the mark goes at the start of the region. Repeating the M-h
command extends the region to subsequent paragraphs.
C-M-h (mark-defun) similarly puts point before, and the
mark after, the current (or following) major top-level definition, or
defun (see section Moving by Defuns). Repeating C-M-h extends
the region to subsequent defuns.
C-x C-p (mark-page) puts point before the current page,
and mark at the end (see section Pages). The mark goes after the
terminating page delimiter (to include it in the region), while point
goes after the preceding page delimiter (to exclude it). A numeric
argument specifies a later page (if positive) or an earlier page (if
negative) instead of the current page.
Finally, C-x h (mark-whole-buffer) sets up the entire
buffer as the region, by putting point at the beginning and the mark at
the end. (In some programs this is called "select all.")
In Transient Mark mode, all of these commands activate the mark.
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Aside from delimiting the region, the mark is also useful for
remembering a spot that you may want to go back to. To make this
feature more useful, each buffer remembers 16 previous locations of the
mark, in the mark ring. Commands that set the mark also push the
old mark onto this ring. To return to a marked location, use C-u
C-SPC (or C-u C-@); this is the command
set-mark-command given a numeric argument. It moves point to
where the mark was, and restores the mark from the ring of former
marks.
If you set set-mark-command-repeat-pop to non-nil,
then when you repeat the character C-SPC after typing
C-u C-SPC, each repetition moves point to a previous mark
position from the ring. The mark positions you move through in this
way are not lost; they go to the end of the ring.
Each buffer has its own mark ring. All editing commands use the current buffer's mark ring. In particular, C-u C-SPC always stays in the same buffer.
Many commands that can move long distances, such as M-<
(beginning-of-buffer), start by setting the mark and saving the
old mark on the mark ring. This is to make it easier for you to move
back later. Searches set the mark if they move point. However, in
Transient Mark mode, these commands do not set the mark when the mark
is already active. You can tell when a command sets the mark because
it displays `Mark set' in the echo area.
If you want to move back to the same place over and over, the mark ring may not be convenient enough. If so, you can record the position in a register for later retrieval (see section Saving Positions in Registers).
The variable mark-ring-max specifies the maximum number of
entries to keep in the mark ring. If that many entries exist and
another one is pushed, the earliest one in the list is discarded. Repeating
C-u C-SPC cycles through the positions currently in the
ring.
The variable mark-ring holds the mark ring itself, as a list of
marker objects, with the most recent first. This variable is local in
every buffer.
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In addition to the ordinary mark ring that belongs to each buffer, Emacs has a single global mark ring. It records a sequence of buffers in which you have recently set the mark, so you can go back to those buffers.
Setting the mark always makes an entry on the current buffer's mark ring. If you have switched buffers since the previous mark setting, the new mark position makes an entry on the global mark ring also. The result is that the global mark ring records a sequence of buffers that you have been in, and, for each buffer, a place where you set the mark.
The command C-x C-SPC (pop-global-mark) jumps to
the buffer and position of the latest entry in the global ring. It also
rotates the ring, so that successive uses of C-x C-SPC take
you to earlier and earlier buffers.
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This document was generated by Mark Kaminski on July, 3 2008 using texi2html 1.70.