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@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, 2009, 2010, 2011  Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Registers, Display, Killing, Top
@chapter Registers
@cindex registers

  Emacs @dfn{registers} are compartments where you can save text,
rectangles, positions, and other things for later use.  Once you save
text or a rectangle in a register, you can copy it into the buffer
once, or many times; once you save a position in a register, you can
jump back to that position once, or many times.

  Each register has a name that consists of a single character, which
we will denote by @var{r}; @var{r} can be a letter (such as @samp{a})
or a number (such as @samp{1}); case matters, so register @samp{a} is
not the same as register @samp{A}.

@findex view-register
  A register can store a position, a piece of text, a rectangle, a
number, a window configuration, or a file name, but only one thing at
any given time.  Whatever you store in a register remains there until
you store something else in that register.  To see what register
@var{r} contains, use @kbd{M-x view-register}:

@table @kbd
@item M-x view-register @key{RET} @var{r}
Display a description of what register @var{r} contains.
@end table

  @dfn{Bookmarks} record files and positions in them, so you can
return to those positions when you look at the file again.
Bookmarks are similar enough in spirit to registers that they
seem to belong in this chapter.

@menu
* Position: RegPos.           Saving positions in registers.
* Text: RegText.              Saving text in registers.
* Rectangle: RegRect.         Saving rectangles in registers.
* Configurations: RegConfig.  Saving window configurations in registers.
* Numbers: RegNumbers.        Numbers in registers.
* Files: RegFiles.            File names in registers.
* Bookmarks::                 Bookmarks are like registers, but persistent.
@end menu

@node RegPos
@section Saving Positions in Registers
@cindex saving position in a register

@table @kbd
@item C-x r @key{SPC} @var{r}
Record the position of point and the current buffer in register
@var{r} (@code{point-to-register}).
@item C-x r j @var{r}
Jump to the position and buffer saved in register @var{r}
(@code{jump-to-register}).
@end table

@kindex C-x r SPC
@findex point-to-register
  Typing @kbd{C-x r @key{SPC}} (@code{point-to-register}), followed by
a character @kbd{@var{r}}, saves both the position of point and the
current buffer in register @var{r}.  The register retains this
information until you store something else in it.

@kindex C-x r j
@findex jump-to-register
  The command @kbd{C-x r j @var{r}} switches to the buffer recorded in
register @var{r}, and moves point to the recorded position.  The
contents of the register are not changed, so you can jump to the saved
position any number of times.

  If you use @kbd{C-x r j} to go to a saved position, but the buffer it
was saved from has been killed, @kbd{C-x r j} tries to create the buffer
again by visiting the same file.  Of course, this works only for buffers
that were visiting files.

@node RegText
@section Saving Text in Registers
@cindex saving text in a register

  When you want to insert a copy of the same piece of text several
times, it may be inconvenient to yank it from the kill ring, since each
subsequent kill moves that entry further down the ring.  An alternative
is to store the text in a register and later retrieve it.

@table @kbd
@item C-x r s @var{r}
Copy region into register @var{r} (@code{copy-to-register}).
@item C-x r i @var{r}
Insert text from register @var{r} (@code{insert-register}).
@item M-x append-to-register @key{RET} @var{r}
Append region to text in register @var{r}.
@item M-x prepend-to-register @key{RET} @var{r}
Prepend region to text in register @var{r}.
@end table

@kindex C-x r s
@findex copy-to-register
  @kbd{C-x r s @var{r}} stores a copy of the text of the region into
the register named @var{r}.  If the mark is inactive, Emacs first
reactivates the mark where it was last set.  The mark is deactivated
at the end of this command.  @xref{Mark}.  @kbd{C-u C-x r s @var{r}},
the same command with a prefix argument, copies the text into register
@var{r} and deletes the text from the buffer as well; you can think of
this as ``moving'' the region text into the register.

@findex append-to-register
@findex prepend-to-register
  @kbd{M-x append-to-register @key{RET} @var{r}} appends the copy of
the text in the region to the text already stored in the register
named @var{r}.  If invoked with a prefix argument, it deletes the
region after appending it to the register.  The command
@code{prepend-to-register} is similar, except that it @emph{prepends}
the region text to the text in the register instead of
@emph{appending} it.

@kindex C-x r i
@findex insert-register
  @kbd{C-x r i @var{r}} inserts in the buffer the text from register
@var{r}.  Normally it leaves point before the text and places the mark
after, but with a numeric argument (@kbd{C-u}) it puts point after the
text and the mark before.

@node RegRect
@section Saving Rectangles in Registers
@cindex saving rectangle in a register

  A register can contain a rectangle instead of linear text.
@xref{Rectangles}, for basic information on how to specify a rectangle
in the buffer.

@table @kbd
@findex copy-rectangle-to-register
@kindex C-x r r
@item C-x r r @var{r}
Copy the region-rectangle into register @var{r}
(@code{copy-rectangle-to-register}).  With numeric argument, delete it as
well.
@item C-x r i @var{r}
Insert the rectangle stored in register @var{r} (if it contains a
rectangle) (@code{insert-register}).
@end table

  The @kbd{C-x r i @var{r}} command inserts a text string if the
register contains one, and inserts a rectangle if the register contains
one.

  See also the command @code{sort-columns}, which you can think of
as sorting a rectangle.  @xref{Sorting}.

@node RegConfig
@section Saving Window Configurations in Registers
@cindex saving window configuration in a register

@findex window-configuration-to-register
@findex frame-configuration-to-register
@kindex C-x r w
@kindex C-x r f
  You can save the window configuration of the selected frame in a
register, or even the configuration of all windows in all frames, and
restore the configuration later.  @xref{Windows}, for information
about window configurations.

@table @kbd
@item C-x r w @var{r}
Save the state of the selected frame's windows in register @var{r}
(@code{window-configuration-to-register}).
@item C-x r f @var{r}
Save the state of all frames, including all their windows, in register
@var{r} (@code{frame-configuration-to-register}).
@end table

  Use @kbd{C-x r j @var{r}} to restore a window or frame configuration.
This is the same command used to restore a cursor position.  When you
restore a frame configuration, any existing frames not included in the
configuration become invisible.  If you wish to delete these frames
instead, use @kbd{C-u C-x r j @var{r}}.

@node RegNumbers
@section Keeping Numbers in Registers
@cindex saving number in a register

  There are commands to store a number in a register, to insert
the number in the buffer in decimal, and to increment it.  These commands
can be useful in keyboard macros (@pxref{Keyboard Macros}).

@table @kbd
@item C-u @var{number} C-x r n @var{r}
@kindex C-x r n
@findex number-to-register
Store @var{number} into register @var{r} (@code{number-to-register}).
@item C-u @var{number} C-x r + @var{r}
@kindex C-x r +
@findex increment-register
Increment the number in register @var{r} by @var{number}
(@code{increment-register}).
@item C-x r i @var{r}
Insert the number from register @var{r} into the buffer.
@end table

  @kbd{C-x r i} is the same command used to insert any other sort of
register contents into the buffer.  @kbd{C-x r +} with no numeric
argument increments the register value by 1; @kbd{C-x r n} with no
numeric argument stores zero in the register.

@node RegFiles
@section Keeping File Names in Registers
@cindex saving file name in a register

  If you visit certain file names frequently, you can visit them more
conveniently if you put their names in registers.  Here's the Lisp code
used to put a file name in a register:

@smallexample
(set-register ?@var{r} '(file . @var{name}))
@end smallexample

@need 3000
@noindent
For example,

@smallexample
(set-register ?z '(file . "/gd/gnu/emacs/19.0/src/ChangeLog"))
@end smallexample

@noindent
puts the file name shown in register @samp{z}.

  To visit the file whose name is in register @var{r}, type @kbd{C-x r j
@var{r}}.  (This is the same command used to jump to a position or
restore a frame configuration.)

@node Bookmarks
@section Bookmarks
@cindex bookmarks

  @dfn{Bookmarks} are somewhat like registers in that they record
positions you can jump to.  Unlike registers, they have long names, and
they persist automatically from one Emacs session to the next.  The
prototypical use of bookmarks is to record ``where you were reading'' in
various files.

@table @kbd
@item C-x r m @key{RET}
Set the bookmark for the visited file, at point.

@item C-x r m @var{bookmark} @key{RET}
@findex bookmark-set
Set the bookmark named @var{bookmark} at point (@code{bookmark-set}).

@item C-x r b @var{bookmark} @key{RET}
@findex bookmark-jump
Jump to the bookmark named @var{bookmark} (@code{bookmark-jump}).

@item C-x r l
@findex list-bookmarks
List all bookmarks (@code{list-bookmarks}).

@item M-x bookmark-save
@findex bookmark-save
Save all the current bookmark values in the default bookmark file.
@end table

@kindex C-x r m
@findex bookmark-set
@kindex C-x r b
@findex bookmark-jump
  The prototypical use for bookmarks is to record one current position
in each of several files.  So the command @kbd{C-x r m}, which sets a
bookmark, uses the visited file name as the default for the bookmark
name.  If you name each bookmark after the file it points to, then you
can conveniently revisit any of those files with @kbd{C-x r b}, and move
to the position of the bookmark at the same time.

@kindex C-x r l
  To display a list of all your bookmarks in a separate buffer, type
@kbd{C-x r l} (@code{list-bookmarks}).  If you switch to that buffer,
you can use it to edit your bookmark definitions or annotate the
bookmarks.  Type @kbd{C-h m} in the bookmark buffer for more
information about its special editing commands.

  When you kill Emacs, Emacs offers to save your bookmark values in your
default bookmark file, @file{~/.emacs.bmk}, if you have changed any
bookmark values.  You can also save the bookmarks at any time with the
@kbd{M-x bookmark-save} command.  The bookmark commands load your
default bookmark file automatically.  This saving and loading is how
bookmarks persist from one Emacs session to the next.

@vindex bookmark-save-flag
  If you set the variable @code{bookmark-save-flag} to 1, each command
that sets a bookmark will also save your bookmarks; this way, you
don't lose any bookmark values even if Emacs crashes.  (The value, if
a number, says how many bookmark modifications should go by between
saving.)

@vindex bookmark-search-size
  Bookmark position values are saved with surrounding context, so that
@code{bookmark-jump} can find the proper position even if the file is
modified slightly.  The variable @code{bookmark-search-size} says how
many characters of context to record on each side of the bookmark's
position.

  Here are some additional commands for working with bookmarks:

@table @kbd
@item M-x bookmark-load @key{RET} @var{filename} @key{RET}
@findex bookmark-load
Load a file named @var{filename} that contains a list of bookmark
values.  You can use this command, as well as @code{bookmark-write}, to
work with other files of bookmark values in addition to your default
bookmark file.

@item M-x bookmark-write @key{RET} @var{filename} @key{RET}
@findex bookmark-write
Save all the current bookmark values in the file @var{filename}.

@item M-x bookmark-delete @key{RET} @var{bookmark} @key{RET}
@findex bookmark-delete
Delete the bookmark named @var{bookmark}.

@item M-x bookmark-insert-location @key{RET} @var{bookmark} @key{RET}
@findex bookmark-insert-location
Insert in the buffer the name of the file that bookmark @var{bookmark}
points to.

@item M-x bookmark-insert @key{RET} @var{bookmark} @key{RET}
@findex bookmark-insert
Insert in the buffer the @emph{contents} of the file that bookmark
@var{bookmark} points to.
@end table