[gnu-emacs] / doc / emacs / mark.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2001, 2002,
@c   2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Mark, Killing, Help, Top
@chapter The Mark and the Region
@cindex mark
@cindex setting a mark
@cindex region

  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 @dfn{the mark} at one end of it, and move point to the other
end.  The text between point and the mark is called @dfn{the region}.

  If the mark is active, the region always extends between point and
the mark, no matter which one comes earlier in the text; each time you
move point, the region changes.  Whenever the mark is active, Emacs
highlights the region.  You can customize the appearance of this
highlighting by changing the @code{region} face (@pxref{Face
Customization}).

  The region persists only until you use it.  The mark is
automatically @dfn{deactivated} after certain non-motion commands,
including any command that changes the text in the buffer.  You can
also explicitly deactivate the mark at any time, by typing @kbd{C-g}
(@pxref{Quitting}).

@vindex highlight-nonselected-windows
  Setting the mark in one buffer has no effect on the marks in other
buffers.  When you return to a buffer with an active mark, the mark is
at the same place as before.  When multiple windows show the same
buffer, they can have different values of point, and thus different
regions, but they all share one common mark position.  @xref{Windows}.
Ordinarily, only the selected window highlights its region; however,
if the variable @code{highlight-nonselected-windows} is
non-@code{nil}, each window highlights its own region.

@menu
* Setting Mark::        Commands to set the mark.
* Marking Objects::     Commands to put region around textual units.
* Using Region::        Summary of ways to operate on contents of the region.
* Mark Ring::           Previous mark positions saved so you can go back there.
* Global Mark Ring::    Previous mark positions in various buffers.
* Shift Selection::     Using shifted cursor motion keys.
* Persistent Mark::     Keeping the mark active all the time.
@end menu

@node Setting Mark
@section Setting the Mark

  Here are some commands for setting the mark:

@table @kbd
@item C-@key{SPC}
Set the mark at point (@code{set-mark-command}).
@item C-@@
The same.
@item C-x C-x
Set the mark at point, and move point where the mark was
(@code{exchange-point-and-mark}).
@item Drag-Mouse-1
Set point and the mark around the text you drag across.
@item Mouse-3
Set the mark at point, then move point to where you click
(@code{mouse-save-then-kill}).
@item @samp{Shifted motion keys}
Set the mark at point if the mark is inactive, then move point.
@end table

@kindex C-SPC
@kindex C-@@
@findex set-mark-command
  The most common way to set the mark is with @kbd{C-@key{SPC}}
(@code{set-mark-command}), which sets the mark where point
is@footnote{There is no @kbd{C-@key{SPC}} character in
@acronym{ASCII}; usually, typing @kbd{C-@key{SPC}} on a text terminal
gives the character @kbd{C-@@}.  This key is also bound to
@code{set-mark-command}, so unless you are unlucky enough to have an
text terminal that behaves differently, you might as well think of
@kbd{C-@@} as @kbd{C-@key{SPC}}.}. You can then move point away,
leaving the mark behind.

  For example, suppose you wish to convert part of the buffer to upper
case.  To accomplish this, go to the beginning of the desired text,
type @kbd{C-@key{SPC}}, and move point until the desired portion of
text is highlighted.  Now type @kbd{C-x C-u} (@code{upcase-region}).
This converts the text in the region to upper case, and then
deactivates the mark.

@kindex C-x C-x
@findex exchange-point-and-mark
  The command @kbd{C-x C-x} (@code{exchange-point-and-mark}) exchanges
the positions of point and the mark, keeping the region unchanged.  If
no mark is active, Emacs first reactivates the mark wherever it was
last set.  @kbd{C-x C-x} is useful when you are satisfied with the
position of point but want to move the other end of the region (where
the mark is).  Using @kbd{C-x C-x} a second time, if necessary, puts
the mark at the new position with point back at its original position.

  You can also set the mark with the mouse.  If you press the left
mouse button (@kbd{down-mouse-1}) and drag the mouse across a range of
text while holding down this button, this sets the mark where you
first pressed the mouse button and puts point where you release it.
Alternatively, clicking the right mouse button (@kbd{mouse-3}) sets
the mark at point and then moves point to where you clicked.  Using
the mouse to mark a region also copies the region into the kill ring
(@pxref{Kill Ring}).  @xref{Mouse Commands}, for a more detailed
description of these mouse commands.

@cindex shift-selection
  Finally, you can set the mark by holding down the shift key while
typing certain cursor motion commands (such as @kbd{S-@key{right}},
@kbd{S-C-f}, @kbd{S-C-n}, etc.)  This is referred to as
@dfn{shift-selection}.  This sets the mark at point before moving
point, but only if there is no active mark set via shift-selection.
The mark set by mouse commands and by shift-selection behaves slightly
differently from the usual mark: any subsequent unshifted cursor
motion command deactivates it automatically.  For details, @xref{Shift
Selection}.

  Whenever the mark is active, you can deactivate it by typing
@kbd{C-g} (@pxref{Quitting}).  The mark is also automatically
deactivated after certain non-motion commands.

@node Marking Objects
@section Commands to Mark Textual Objects

@cindex marking sections of text
  Here are the commands for placing point and the mark around a textual
object such as a word, list, paragraph or page:

@table @kbd
@item M-@@
Set mark after end of next word (@code{mark-word}).  This does not
move point.
@item C-M-@@
Set mark after end of following balanced expression
(@code{mark-sexp}).  This does not move point.
@item M-h
Move point to the beginning of the current paragraph, and set mark at
the end (@code{mark-paragraph}).
@item C-M-h
Move point to the beginning of the current defun, and set mark at the
end (@code{mark-defun}).
@item C-x C-p
Move point to the beginning of the current page, and set mark at the
end (@code{mark-page}).
@item C-x h
Move point to the beginning of the buffer, and set mark at the end
(@code{mark-whole-buffer}).
@end table

@findex mark-word
@findex mark-sexp
@kbd{M-@@} (@code{mark-word}) puts the mark at the end of the next
word, while @kbd{C-M-@@} (@code{mark-sexp}) puts it at the end of the
next balanced expression (@pxref{Expressions}).  These commands handle
arguments just like @kbd{M-f} and @kbd{C-M-f}.

@kindex C-x h
@findex mark-whole-buffer
   The other commands in the above list set both point and mark, so as
to delimit an object in the buffer.  @kbd{M-h} (@code{mark-paragraph})
moves point to the beginning of the paragraph that surrounds or
follows point, and sets the mark at the end of that paragraph
(@pxref{Paragraphs}).  As a special exception, repeated invocations of
@kbd{M-h} extend the region to subsequent paragraphs.  This is
convenient for indenting, case-converting, or killing entire
paragraphs.

  The @kbd{M-h} command accepts prefix arguments.  If the argument's
value is positive, @kbd{M-h} marks that many paragraphs starting with
the one surrounding point; therefore, @kbd{C-u M-h} is equivalent to
@kbd{M-h M-h M-h M-h}.  If the prefix argument is @minus{}@var{n},
@kbd{M-h} marks @var{n} paragraphs running back from the one
surrounding point; in this case, point moves forward to the end of
that paragraph, and the mark goes at the start of the region.

  Similarly, @kbd{C-M-h} (@code{mark-defun}) sets mark and point
around major top-level definitions (@pxref{Moving by Defuns}), and
@kbd{C-x C-p} (@code{mark-page}) does the same for pages
(@pxref{Pages}).  These treat repeated invokations and prefix
arguments similarly to @code{mark-paragraph}.

  Finally, @kbd{C-x h} (@code{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.'')

@node Using Region
@section Operating on the Region

@cindex operations on a marked region
  Once you have a region, here are some of the ways you can operate on
it:

@itemize @bullet
@item
Kill it with @kbd{C-w} (@pxref{Killing}).
@item
Copy it to the kill ring with @kbd{M-w} (@pxref{Yanking}).
@item
Convert case with @kbd{C-x C-l} or @kbd{C-x C-u} (@pxref{Case}).
@item
Undo changes within it using @kbd{C-u C-/} (@pxref{Undo}).
@item
Replace text within it using @kbd{M-%} (@pxref{Query Replace}).
@item
Indent it with @kbd{C-x @key{TAB}} or @kbd{C-M-\} (@pxref{Indentation}).
@item
Fill it as text with @kbd{M-x fill-region} (@pxref{Filling}).
@item
Print hardcopy with @kbd{M-x print-region} (@pxref{Printing}).
@item
Evaluate it as Lisp code with @kbd{M-x eval-region} (@pxref{Lisp Eval}).
@item
Save it in a register with @kbd{C-x r s} (@pxref{Registers}).
@item
Save it in a buffer or a file (@pxref{Accumulating Text}).
@end itemize

  Most commands that operate on the text in the region have the word
@code{region} in their names.

  Some commands have a default behavior when the region is inactive,
but operate on the text in the region if the region is active.  For
example, @kbd{M-$} (@code{ispell-word}) normally checks the spelling
of the word at point, but it checks the text in the region if the
region is active (@pxref{Spelling}).  Normally, such commands use
their default behavior if the region is empty (i.e., if mark and point
are at the same position).  If you want them to operate on the empty
region, change the variable @code{use-empty-active-region} to
@code{t}.

@cindex Delete Selection mode
@cindex mode, Delete Selection
@findex delete-selection-mode
  If you enable Delete Selection mode, a minor mode, then inserting
text while the region is active causes the selected text to be deleted
first.  This also deactivates the mark.  Many graphical applications
follow this convention, but Emacs does not.  To toggle Delete
Selection mode on or off, type @kbd{M-x delete-selection-mode}.
Another effect of this mode is that some keys, such as @key{DEL} and
@kbd{C-d}, always kill the region if one exists.

@node Mark Ring
@section The Mark Ring

@cindex mark ring
  Aside from delimiting the region, the mark is also useful for
remembering spots that you may want to go back to.  Each buffer
remembers 16 previous locations of the mark, in the @dfn{mark ring}.
Commands that set the mark also push the old mark onto this ring.

@table @kbd
@item C-@key{SPC} C-@key{SPC}
Set the mark, pushing it onto the mark ring, without activating it.
@item C-u C-@key{SPC}
Move point to where the mark was, and restore the mark from the ring
of former marks.
@end table

@kindex C-SPC C-SPC
  The command C-@key{SPC} C-@key{SPC} is handy when you want to use
the mark to remember a position to which you may wish to return.  It
pushes the current point onto the mark ring, without activating the
mark (which would cause Emacs to highlight the region).  This is
actually two consecutive invocations of @kbd{C-@key{SPC}}
(@code{set-mark-command}); the first @kbd{C-@key{SPC}} sets the mark,
and the second @kbd{C-@key{SPC}} deactivates it.  (When Transient Mark
mode is off, C-@key{SPC} C-@key{SPC} instead activates Transient Mark
mode temporarily.  @xref{Persistent Mark}.)

@kindex C-u C-SPC
  To return to a marked position, use @code{set-mark-command} with a
prefix argument: @kbd{C-u C-@key{SPC}}.  This moves point to where the
mark was, and deactivates the mark if it was active.  Each subsequent
@kbd{C-u C-@key{SPC}} jumps to a prior position stored in the mark
ring.  The positions you move through in this way are not lost; they
go to the end of the ring.

@vindex set-mark-command-repeat-pop
  If you set @code{set-mark-command-repeat-pop} to non-@code{nil},
then immediately after you type @kbd{C-u C-@key{SPC}}, you can type
@kbd{C-@key{SPC}} instead of @kbd{C-u C-@key{SPC}} to cycle through
the mark ring.  By default, @code{set-mark-command-repeat-pop} is
@code{nil}.

  Each buffer has its own mark ring.  All editing commands use the
current buffer's mark ring.  In particular, @kbd{C-u C-@key{SPC}}
always stays in the same buffer.

@vindex mark-ring-max
  The variable @code{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
@kbd{C-u C-@key{SPC}} cycles through the positions currently in the
ring.

@vindex mark-even-if-inactive
  If the variable @code{mark-even-if-inactive} is @code{nil}, commands
can only use the mark and the region when it is active.  This variable
is non-@code{nil} by default.

  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 (@pxref{RegPos,, Saving Positions in
Registers}).

@node Global Mark Ring
@section The Global Mark Ring
@cindex global mark ring

  In addition to the ordinary mark ring that belongs to each buffer,
Emacs has a single @dfn{global mark ring}.  Each time you set a mark,
in any buffer, this is recorded in the global mark ring in addition to
the current buffer's own mark ring.

@kindex C-x C-@key{SPC}
@findex pop-global-mark
  The command @kbd{C-x C-@key{SPC}} (@code{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 @kbd{C-x C-@key{SPC}} take
you to earlier buffers and mark positions.

@node Shift Selection
@section Shift Selection
@cindex shift-selection

  If you hold down the shift key while typing a cursor motion command,
this sets the mark before moving point, so that the region extends
from the original position of point to its new position.  This
feature, newly introduced in Emacs 23, is referred to as
@dfn{shift-selection}.  It is similar to the way text is selected in
other editors.

  The mark set via shift-selection behaves a little differently from
what we have described above.  Firstly, in addition to the usual ways
of deactivating the mark (such as changing the buffer text or typing
@kbd{C-g}), the mark is deactivated by any @emph{unshifted} cursor
motion command.  Secondly, any subsequent @emph{shifted} cursor motion
command avoids setting the mark anew.  Therefore, a series of shifted
cursor motion commands will continuously extend the region.

  Shift-selection only works if the shifted cursor motion key is not
already bound to a separate command (@pxref{Customization}).  For
example, if you bind @kbd{S-C-f} to another command, typing
@kbd{S-C-f} runs that command instead of performing a shift-selected
version of @kbd{C-f} (@code{forward-char}).

  A mark set via mouse commands behaves the same as a mark set via
shift-selection (@pxref{Setting Mark}).  For example, if you specify a
region by dragging the mouse, you can continue to extend the region
using shifted cursor motion commands.  In either case, any unshifted
cursor motion command deactivates the mark.

  To turn off shift-selection, set @code{shift-select-mode} to
@code{nil}.  Doing this does not disable setting the mark via mouse
commands.

@node Persistent Mark
@section Persistent Marks
@cindex mode, Transient Mark
@cindex Transient Mark mode
@cindex highlighting region
@cindex region highlighting
@cindex Zmacs mode

  By default, the region is highlighted whenever it exists, and
disappears once you use it or explicitly deactivate the mark.  This
behavior is called Transient Mark mode@footnote{It is also sometimes
called @dfn{Zmacs mode}, because the Zmacs editor on the MIT Lisp
Machine handled the mark in a similar way.}.

@findex transient-mark-mode
  Turning off Transient Mark mode switches Emacs to an alternative
mode of operation, which was the default prior to Emacs 23.  When
Transient Mark mode is off, the mark is persistent: it is @emph{never}
deactivated, but can be set to different locations using commands such
as @kbd{C-@key{SPC}}.  After the first time you set the mark in a
buffer, there is always a region in that buffer.  Emacs will not
highlight the region, because that would be a nuisance.  As a special
exception, the region is temporarily highlighted after it is set with
the mouse.

  To turn off Transient Mark mode, type @kbd{M-x transient-mark-mode}.
This command toggles the mode; you can use the same command to turn
Transient Mark mode on again.  You can also turn off Transient Mark
mode using the menu bar: in the @samp{Options} menu, toggle the
@samp{Active Region Highlighting} menu item.

  Here are the details of how Emacs behaves when Transient Mark mode
is off:

@itemize @bullet
@item
Emacs does not show where the mark is located---you have to remember.
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 check the
location of the mark by using @kbd{C-x C-x}, which exchanges the
positions of the point and the mark (@pxref{Setting Mark}).

@item
Many commands that insert text, such as @kbd{C-y} (@code{yank}),
position point and the mark at opposite ends of the inserted text, so
that the region consists of the text just inserted.  You can tell when
a command sets the mark because it displays @samp{Mark set} in the
echo area.

@item
Many commands that move point long distances, like @kbd{M-<} and
@kbd{C-s}, first set the mark where point was.

@item
Some commands that ordinarily operate on the region, if one exists,
act instead on the entire buffer.  For instance, @kbd{C-x u} normally
reverses changes within the region if one exists; when Transient Mark
mode is off, it acts on the entire buffer.  However, you can type
@kbd{C-u C-x u} to make it operate on the region.  @xref{Undo}.  Other
commands that act this way are identified in their own documentation.
@end itemize

  While Transient Mark mode is off, you can activate it temporarily
using @kbd{C-@key{SPC} C-@key{SPC}} or @kbd{C-u C-x C-x}.

@table @kbd
@item C-@key{SPC} C-@key{SPC}
@kindex C-@key{SPC} C-@key{SPC}
Set the mark at point (like plain @kbd{C-@key{SPC}}) and enable
Transient Mark mode just once, until the mark is deactivated.  (This
is not really a separate command; you are using the @kbd{C-@key{SPC}}
command twice.)

@item C-u C-x C-x
@kindex C-u C-x C-x
Activate the mark without changing it; enable Transient Mark mode just
once, until the mark is deactivated.  (This is the @kbd{C-x C-x}
command, @code{exchange-point-and-mark}, with a prefix argument.)
@end table

  These commands set or activate the mark, and enable Transient Mark
mode only until the mark is deactivated.  One reason you may want to
use them is that some commands operate on the entire buffer instead of
the region when Transient Mark mode is off.  Enabling Transient Mark
mode momentarily gives you a way to use these commands on the region.

@ignore
   arch-tag: f35e4d82-911b-4cfc-a3d7-3c87b2abba20
@end ignore