Use xfree, not free, to avoid crash with --enable-checking=xmallocoverrun.

[bpt/emacs.git] / doc / emacs / mark.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985-1987, 1993-1995, 1997, 2001-2011
@c   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}.
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.

  Setting the mark at a position in the text also @dfn{activates} it.
When the mark is active, Emacs indicates the extent of the region by
highlighting the text within it, using the @code{region} face
(@pxref{Face Customization}).  After certain non-motion commands,
including any command that changes the text in the buffer, Emacs
automatically @dfn{deactivates} the mark; this turns off the
highlighting.  You can also explicitly deactivate the mark at any
time, by typing @kbd{C-g} (@pxref{Quitting}).

  This default behavior is known as Transient Mark mode.  Disabling
Transient Mark mode switches Emacs to an alternative behavior, in
which the region is usually not highlighted.  @xref{Disabled Transient Mark}.

@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.
* Disabled Transient Mark:: Leaving regions unhighlighted by default.
@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, and activate it (@code{set-mark-command}).
@item C-@@
The same.
@item C-x C-x
Set the mark at point, and activate it; then move point where the mark
used to be (@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 cursor motion keys}
Set the mark at point if the mark is inactive, then move point.
@xref{Shift Selection}.
@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})@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
a text terminal that behaves differently, you might as well think of
@kbd{C-@@} as @kbd{C-@key{SPC}}.}.  This sets the mark where point is,
and activates it.  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 one end 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.

  Whenever the mark is active, you can deactivate it by typing
@kbd{C-g} (@pxref{Quitting}).  Most commands that operate on the
region also automatically deactivate the mark, like @kbd{C-x C-u} in
the above example.

  Instead of setting the mark in order to operate on a region, you can
also use it to ``remember'' a position in the buffer (by typing
@kbd{C-@key{SPC} C-@key{SPC}}), and later jump back there (by typing
@kbd{C-u C-@key{SPC}}).  @xref{Mark Ring}, for details.

@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.  @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.  Normally, if the mark is inactive, this
command first reactivates the mark wherever it was last set, to ensure
that the region is left highlighted.  However, if you call it with a
prefix argument, it leaves the mark inactive and the region
unhighlighted; you can use this to jump to the mark in a manner
similar to @kbd{C-u C-@key{SPC}}.

  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, 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.  @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 called @dfn{shift-selection}.
It 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}.

  Many commands that insert text, such as @kbd{C-y} (@code{yank}), set
the mark at the other end of the inserted text, without activating it.
This lets you easily return to that position (@pxref{Mark Ring}).  You
can tell that a command does this when it shows @samp{Mark set} in the
echo area.

@cindex primary selection
  Under X, every time the region changes while the mark is active,
Emacs saves the text in the region to the @dfn{primary selection}.
This lets you insert that text into other X applications with
@kbd{mouse-2} clicks.  @xref{Primary Selection}.

@node Marking Objects
@section Commands to Mark Textual Objects

@cindex marking sections of text
  Here are 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

@kindex M-@@
@findex mark-word
  @kbd{M-@@} (@code{mark-word}) sets the mark at the end of the next
word (@pxref{Words}, for information about words).  Repeated
invocations of this command extend the region by advancing the mark
one word at a time.  As an exception, if the mark is active and
located before point, @kbd{M-@@} moves the mark backwards from its
current position one word at a time.

  This command also accepts a numeric argument @var{n}, which tells it
to advance the mark by @var{n} words.  A negative argument moves the
mark back by @var{n} words.

@kindex C-M-@@
@findex mark-sexp
  Similarly, @kbd{C-M-@@} (@code{mark-sexp}) puts the mark at the end
of the next balanced expression (@pxref{Expressions}).  Repeated
invocations extend the region to subsequent expressions, while
positive or negative numeric arguments move the mark forward or
backward by the specified number of expressions.

   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})
marks paragraphs (@pxref{Paragraphs}), @kbd{C-M-h} (@code{mark-defun})
marks top-level definitions (@pxref{Moving by Defuns}), and @kbd{C-x
C-p} (@code{mark-page}) marks pages (@pxref{Pages}).  Repeated
invocations again play the same role, extending the region to
consecutive objects; similarly, numeric arguments specify how many
objects to move the mark by.

@kindex C-x h
@findex mark-whole-buffer
@cindex select all
  @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.

@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
Check the spelling of words within it with @kbd{M-$} (@pxref{Spelling}).
@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

  Some commands have a default behavior when the mark is inactive, but
operate on the text in the region if the mark 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}.

@vindex mark-even-if-inactive
  Other commands always operate on the text in the region, and have no
default behavior.  Such commands usually have the word @code{region}
in their names, like @kbd{C-w} (@code{kill-region}) and @code{C-x C-u}
(@code{upcase-region}).  If the mark is inactive, they operate on the
``inactive region''---that is, on the text between point and the
position at which the mark was last set (@pxref{Mark Ring}).  To
disable this behavior, change the variable
@code{mark-even-if-inactive} to @code{nil}.  Then these commands will
instead signal an error if the mark is inactive.

@cindex Delete Selection mode
@cindex mode, Delete Selection
@findex delete-selection-mode
  By default, text insertion occurs normally even if the mark is
active---for example, typing @kbd{a} inserts the character @samp{a},
then deactivates the mark.  If you enable Delete Selection mode, a
minor mode, then inserting text while the mark is active causes the
text in the region to be deleted first.  To toggle Delete Selection
mode on or off, type @kbd{M-x delete-selection-mode}.

@node Mark Ring
@section The Mark Ring

@cindex mark ring
  Each buffer remembers previous locations of the mark, in the
@dfn{mark ring}.  Commands that set the mark also push the old mark
onto this ring.  One of the uses of the mark ring is to remember spots
that you may want to go back to.

@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 @kbd{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, @kbd{C-@key{SPC} C-@key{SPC}} instead activates Transient
Mark mode temporarily; @pxref{Disabled Transient 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.  This defaults to 16 entries.  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.

  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{Position Registers,, Saving
Positions in Registers}).

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

@vindex global-mark-ring-max
  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.  The length of this ring can be
controlled by @code{global-mark-ring-max}, and is 16 by default.

@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
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 adjust 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 so does not disable setting the mark via mouse
commands.

@node Disabled Transient Mark
@section Disabling Transient Mark Mode
@cindex mode, Transient Mark
@cindex Transient Mark mode
@cindex highlighting region
@cindex region highlighting
@cindex Zmacs mode
@findex transient-mark-mode

  The default behavior of the mark and region, in which setting the
mark activates it and highlights the region, is called Transient Mark
mode.  This is a minor mode that is enabled by default.  It can be
toggled with @kbd{M-x transient-mark-mode}, or with the @samp{Active
Region Highlighting} menu item in the @samp{Options} menu.  Turning it
off switches Emacs to an alternative mode of operation:

@itemize @bullet
@item
Setting the mark, with commands like @kbd{C-@key{SPC}} or @kbd{C-x
C-x}, does not highlight the region.  Therefore, you can't tell by
looking 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.  You can also check where the
mark is by using @kbd{C-x C-x}, which exchanges the positions of the
point and the mark (@pxref{Setting Mark}).

@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, which ordinarily act on the region when the mark is
active, no longer do so.  For example, normally @kbd{M-%}
(@code{query-replace}) performs replacements within the region, if the
mark is active.  When Transient Mark mode is off, it always operates
from point to the end of the buffer.  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 and enable Transient Mark mode temporarily, until
the mark is next 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.

  When you specify a region with the mouse (@pxref{Setting Mark}), or
with shift-selection (@pxref{Shift Selection}), this likewise
activates Transient Mark mode temporarily and highlights the region.