(f90-font-lock-keywords-1): Fix highlighting of `type' forms.

[bpt/emacs.git] / man / killing.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985,86,87,93,94,95,97,00,2001 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@iftex
@chapter Killing and Moving Text

  @dfn{Killing} means erasing text and copying it into the @dfn{kill
ring}, from which it can be retrieved by @dfn{yanking} it.  Some systems
use the terms ``cutting'' and ``pasting'' for these operations.

  The most common way of moving or copying text within Emacs is to kill it
and later yank it elsewhere in one or more places.  This is very safe
because Emacs remembers several recent kills, not just the last one.  It
is versatile, because the many commands for killing syntactic units can
also be used for moving those units.  But there are other ways of
copying text for special purposes.

  On terminals that support multiple windows for multiple applications,
the kill commands also provide a way to select text for other applications
to copy, and the Emacs yank commands can access selections made by
other programs.

  Emacs has only one kill ring for all buffers, so you can kill text in
one buffer and yank it in another buffer.

@end iftex

@node Killing, Yanking, Mark, Top
@section Deletion and Killing

@cindex killing text
@cindex cutting text
@cindex deletion
  Most commands which erase text from the buffer save it in the kill
ring so that you can move or copy it to other parts of the buffer.
These commands are known as @dfn{kill} commands.  The rest of the
commands that erase text do not save it in the kill ring; they are known
as @dfn{delete} commands.  (This distinction is made only for erasure of
text in the buffer.)  If you do a kill or delete command by mistake, you
can use the @kbd{C-x u} (@code{undo}) command to undo it
(@pxref{Undo}).

@vindex kill-read-only-ok
@cindex read-only text, killing
  You cannot kill read-only text, since such text does not allow any
kind of modification.  But some users like to use the kill commands to
copy read-only text into the kill ring, without actually changing it.
If you set the variable @code{kill-read-only-ok} to a non-@code{nil}
value, the kill commands work specially in a read-only buffer: they
move over text, and copy it to the kill ring, without actually
deleting it from the buffer.  When this happens, a message in the echo
area tells you what is happening.

  The delete commands include @kbd{C-d} (@code{delete-char}) and
@key{DEL} (@code{delete-backward-char}), which delete only one
character at a time, and those commands that delete only spaces or
newlines.  Commands that can destroy significant amounts of nontrivial
data generally do a kill operation instead.  The commands' names and
individual descriptions use the words @samp{kill} and @samp{delete} to
say which kind of operation they perform.

  On window systems, the most recent kill done in Emacs is also the
primary selection, if it is more recent than any selection you made in
another program.  This means that the paste commands of other window
applications copy the text that you killed in Emacs.

@cindex Delete Selection mode
@cindex mode, Delete Selection
@findex delete-selection-mode
  Many window systems follow the convention that insertion while text
is selected deletes the selected text.  You can make Emacs behave this
way by enabling Delete Selection mode, with @kbd{M-x
delete-selection-mode}, or using Custom.  Another effect of this mode
is that @key{DEL}, @kbd{C-d} and some other keys, when a selection
exists, will kill the whole selection.  It also enables Transient Mark
mode (@pxref{Transient Mark}).

@menu
* Deletion::            Commands for deleting small amounts of text and
                          blank areas.
* Killing by Lines::    How to kill entire lines of text at one time.
* Other Kill Commands:: Commands to kill large regions of text and
                          syntactic units such as words and sentences. 
@end menu

@need 1500
@node Deletion
@subsection Deletion
@findex delete-backward-char
@findex delete-char

  Deletion means erasing text and not saving it in the kill ring.  For
the most part, the Emacs commands that delete text are those that
erase just one character or only whitespace.

@table @kbd
@item C-d
@itemx @key{Delete}
Delete next character (@code{delete-char}).  If your keyboard has a
@key{Delete} function key (usually located in the edit keypad), Emacs
binds it to @code{delete-char} as well.
@item @key{DEL}
@itemx @key{BS}
Delete previous character (@code{delete-backward-char}).  Some keyboards
refer to this key as a ``backspace key'' and label it with a left arrow.
@item M-\
Delete spaces and tabs around point (@code{delete-horizontal-space}).
@item M-@key{SPC}
Delete spaces and tabs around point, leaving one space
(@code{just-one-space}).
@item C-x C-o
Delete blank lines around the current line (@code{delete-blank-lines}).
@item M-^
Join two lines by deleting the intervening newline, along with any
indentation following it (@code{delete-indentation}).
@end table

@kindex DEL
@kindex C-d
  The most basic delete commands are @kbd{C-d} (@code{delete-char}) and
@key{DEL} (@code{delete-backward-char}).  @kbd{C-d} deletes the
character after point, the one the cursor is ``on top of.''  This
doesn't move point.  @key{DEL} deletes the character before the cursor,
and moves point back.  You can delete newlines like any other characters
in the buffer; deleting a newline joins two lines.  Actually, @kbd{C-d}
and @key{DEL} aren't always delete commands; when given arguments, they
kill instead, since they can erase more than one character this way.

@kindex BACKSPACE
@kindex BS
@kindex DELETE
  Every keyboard has a large key, labeled @key{DEL}, @key{BACKSPACE},
@key{BS} or @key{DELETE}, which is a short distance above the
@key{RET} or @key{ENTER} key and is normally used for erasing what you
have typed.  Regardless of the actual name on the key, in Emacs it is
equivalent to @key{DEL}---or it should be.

  Many keyboards (including standard PC keyboards) have a
@key{BACKSPACE} key a short ways above @key{RET} or @key{ENTER}, and a
@key{DELETE} key elsewhere.  In that case, the @key{BACKSPACE} key is
@key{DEL}, and the @key{DELETE} key is equivalent to @kbd{C-d}---or it
should be.

  Why do we say ``or it should be''?  When Emacs starts up using a
window system, it determines automatically which key or keys should be
equivalent to @key{DEL}.  As a result, @key{BACKSPACE} and/or @key{DELETE}
keys normally do the right things.  But in some unusual cases Emacs
gets the wrong information from the system.  If these keys don't do
what they ought to do, you need to tell Emacs which key to use for
@key{DEL}.  @xref{DEL Does Not Delete}, for how to do this.

@findex normal-erase-is-backspace-mode
  On most text-only terminals, Emacs cannot tell which keys the
keyboard really has, so it follows a uniform plan which may or may not
fit your keyboard.  The uniform plan is that the ASCII @key{DEL}
character deletes, and the ASCII @key{BS} (backspace) character asks
for help (it is the same as @kbd{C-h}).  If this is not right for your
keyboard, such as if you find that the key which ought to delete backwards
enters Help instead, see @ref{DEL Does Not Delete}.

@kindex M-\
@findex delete-horizontal-space
@kindex M-SPC
@findex just-one-space
  The other delete commands are those which delete only whitespace
characters: spaces, tabs and newlines.  @kbd{M-\}
(@code{delete-horizontal-space}) deletes all the spaces and tab
characters before and after point.  @kbd{M-@key{SPC}}
(@code{just-one-space}) does likewise but leaves a single space after
point, regardless of the number of spaces that existed previously (even
if there were none before).

  @kbd{C-x C-o} (@code{delete-blank-lines}) deletes all blank lines
after the current line.  If the current line is blank, it deletes all
blank lines preceding the current line as well (leaving one blank line,
the current line).

  @kbd{M-^} (@code{delete-indentation}) joins the current line and the
previous line, by deleting a newline and all surrounding spaces, usually
leaving a single space.  @xref{Indentation,M-^}.

@node Killing by Lines
@subsection Killing by Lines

@table @kbd
@item C-k
Kill rest of line or one or more lines (@code{kill-line}).
@end table

@kindex C-k
@findex kill-line
  The simplest kill command is @kbd{C-k}.  If given at the beginning of
a line, it kills all the text on the line, leaving it blank.  When used
on a blank line, it kills the whole line including its newline.  To kill
an entire non-blank line, go to the beginning and type @kbd{C-k} twice.

  More generally, @kbd{C-k} kills from point up to the end of the line,
unless it is at the end of a line.  In that case it kills the newline
following point, thus merging the next line into the current one.
Spaces and tabs that you can't see at the end of the line are ignored
when deciding which case applies, so if point appears to be at the end
of the line, you can be sure @kbd{C-k} will kill the newline.

  When @kbd{C-k} is given a positive argument, it kills that many lines
and the newlines that follow them (however, text on the current line
before point is not killed).  With a negative argument @minus{}@var{n}, it
kills @var{n} lines preceding the current line (together with the text
on the current line before point).  Thus, @kbd{C-u - 2 C-k} at the front
of a line kills the two previous lines.

  @kbd{C-k} with an argument of zero kills the text before point on the
current line.

@vindex kill-whole-line
  If the variable @code{kill-whole-line} is non-@code{nil}, @kbd{C-k} at
the very beginning of a line kills the entire line including the
following newline.  This variable is normally @code{nil}.

@node Other Kill Commands
@subsection Other Kill Commands
@findex kill-region
@kindex C-w

@table @kbd
@item C-w
Kill region (from point to the mark) (@code{kill-region}).
@item M-d
Kill word (@code{kill-word}).  @xref{Words}.
@item M-@key{DEL}
Kill word backwards (@code{backward-kill-word}).
@item C-x @key{DEL}
Kill back to beginning of sentence (@code{backward-kill-sentence}).
@xref{Sentences}.
@item M-k
Kill to end of sentence (@code{kill-sentence}).
@item C-M-k
Kill the following balanced expression (@code{kill-sexp}).  @xref{Expressions}.
@item M-z @var{char}
Kill through the next occurrence of @var{char} (@code{zap-to-char}).
@end table

  A kill command which is very general is @kbd{C-w}
(@code{kill-region}), which kills everything between point and the
mark.  With this command, you can kill any contiguous sequence of
characters, if you first set the region around them.

@kindex M-z
@findex zap-to-char
  A convenient way of killing is combined with searching: @kbd{M-z}
(@code{zap-to-char}) reads a character and kills from point up to (and
including) the next occurrence of that character in the buffer.  A
numeric argument acts as a repeat count.  A negative argument means to
search backward and kill text before point.

  Other syntactic units can be killed: words, with @kbd{M-@key{DEL}}
and @kbd{M-d} (@pxref{Words}); balanced expressions, with @kbd{C-M-k}
(@pxref{Expressions}); and sentences, with @kbd{C-x @key{DEL}} and
@kbd{M-k} (@pxref{Sentences}).@refill

  You can use kill commands in read-only buffers.  They don't actually
change the buffer, and they beep to warn you of that, but they do copy
the text you tried to kill into the kill ring, so you can yank it into
other buffers.  Most of the kill commands move point across the text
they copy in this way, so that successive kill commands build up a
single kill ring entry as usual.

@node Yanking, Accumulating Text, Killing, Top
@section Yanking
@cindex moving text
@cindex copying text
@cindex kill ring
@cindex yanking
@cindex pasting

  @dfn{Yanking} means reinserting text previously killed.  This is what
some systems call ``pasting.''  The usual way to move or copy text is to
kill it and then yank it elsewhere one or more times.

@table @kbd
@item C-y
Yank last killed text (@code{yank}).
@item M-y
Replace text just yanked with an earlier batch of killed text
(@code{yank-pop}).
@item M-w
Save region as last killed text without actually killing it
(@code{kill-ring-save}).
@item C-M-w
Append next kill to last batch of killed text (@code{append-next-kill}).
@end table

  On window systems, if there is a current selection in some other
application, and you selected it more recently than you killed any
text in Emacs, @kbd{C-y} copies the selection instead of text
killed within Emacs.

@menu
* Kill Ring::		Where killed text is stored.  Basic yanking.
* Appending Kills::	Several kills in a row all yank together.
* Earlier Kills::	Yanking something killed some time ago.
@end menu

@node Kill Ring
@subsection The Kill Ring

  All killed text is recorded in the @dfn{kill ring}, a list of blocks of
text that have been killed.  There is only one kill ring, shared by all
buffers, so you can kill text in one buffer and yank it in another buffer.
This is the usual way to move text from one file to another.
(@xref{Accumulating Text}, for some other ways.)

@kindex C-y
@findex yank
  The command @kbd{C-y} (@code{yank}) reinserts the text of the most recent
kill.  It leaves the cursor at the end of the text.  It sets the mark at
the beginning of the text.  @xref{Mark}.

  @kbd{C-u C-y} leaves the cursor in front of the text, and sets the
mark after it.  This happens only if the argument is specified with just
a @kbd{C-u}, precisely.  Any other sort of argument, including @kbd{C-u}
and digits, specifies an earlier kill to yank (@pxref{Earlier Kills}).

@cindex yanking and text properties
@vindex yank-excluded-properties
  The yank commands discard certain text properties from the text that
is thanked, those that might lead to annoying results.  For instance,
they discard text properties that respond to the mouse or specify key
bindings.  The variable @code{yank-excluded-properties} specifies the
properties to discard.  Yanking of register contents and rectangles
also discard these properties.

@kindex M-w
@findex kill-ring-save
  To copy a block of text, you can use @kbd{M-w}
(@code{kill-ring-save}), which copies the region into the kill ring
without removing it from the buffer.  This is approximately equivalent
to @kbd{C-w} followed by @kbd{C-x u}, except that @kbd{M-w} does not
alter the undo history and does not temporarily change the screen.

@node Appending Kills
@subsection Appending Kills

@cindex appending kills in the ring
@cindex television
  Normally, each kill command pushes a new entry onto the kill ring.
However, two or more kill commands in a row combine their text into a
single entry, so that a single @kbd{C-y} yanks all the text as a unit,
just as it was before it was killed.

  Thus, if you want to yank text as a unit, you need not kill all of it
with one command; you can keep killing line after line, or word after
word, until you have killed it all, and you can still get it all back at
once.

  Commands that kill forward from point add onto the end of the previous
killed text.  Commands that kill backward from point add text onto the
beginning.  This way, any sequence of mixed forward and backward kill
commands puts all the killed text into one entry without rearrangement.
Numeric arguments do not break the sequence of appending kills.  For
example, suppose the buffer contains this text:

@example
This is a line @point{}of sample text.
@end example

@noindent
with point shown by @point{}.  If you type @kbd{M-d M-@key{DEL} M-d
M-@key{DEL}}, killing alternately forward and backward, you end up with
@samp{a line of sample} as one entry in the kill ring, and @samp{This
is@ @ text.} in the buffer.  (Note the double space between @samp{is}
and @samp{text}, which you can clean up with @kbd{M-@key{SPC}} or
@kbd{M-q}.)

  Another way to kill the same text is to move back two words with
@kbd{M-b M-b}, then kill all four words forward with @kbd{C-u M-d}.
This produces exactly the same results in the buffer and in the kill
ring.  @kbd{M-f M-f C-u M-@key{DEL}} kills the same text, all going
backward; once again, the result is the same.  The text in the kill ring
entry always has the same order that it had in the buffer before you
killed it.

@kindex C-M-w
@findex append-next-kill
  If a kill command is separated from the last kill command by other
commands (not just numeric arguments), it starts a new entry on the kill
ring.  But you can force it to append by first typing the command
@kbd{C-M-w} (@code{append-next-kill}) right before it.  The @kbd{C-M-w}
tells the following command, if it is a kill command, to append the text
it kills to the last killed text, instead of starting a new entry.  With
@kbd{C-M-w}, you can kill several separated pieces of text and
accumulate them to be yanked back in one place.@refill

  A kill command following @kbd{M-w} does not append to the text that
@kbd{M-w} copied into the kill ring.

@node Earlier Kills
@subsection Yanking Earlier Kills

@cindex yanking previous kills
@kindex M-y
@findex yank-pop
  To recover killed text that is no longer the most recent kill, use the
@kbd{M-y} command (@code{yank-pop}).  It takes the text previously
yanked and replaces it with the text from an earlier kill.  So, to
recover the text of the next-to-the-last kill, first use @kbd{C-y} to
yank the last kill, and then use @kbd{M-y} to replace it with the
previous kill.  @kbd{M-y} is allowed only after a @kbd{C-y} or another
@kbd{M-y}.

  You can understand @kbd{M-y} in terms of a ``last yank'' pointer which
points at an entry in the kill ring.  Each time you kill, the ``last
yank'' pointer moves to the newly made entry at the front of the ring.
@kbd{C-y} yanks the entry which the ``last yank'' pointer points to.
@kbd{M-y} moves the ``last yank'' pointer to a different entry, and the
text in the buffer changes to match.  Enough @kbd{M-y} commands can move
the pointer to any entry in the ring, so you can get any entry into the
buffer.  Eventually the pointer reaches the end of the ring; the next
@kbd{M-y} loops back around to the first entry again.

  @kbd{M-y} moves the ``last yank'' pointer around the ring, but it does
not change the order of the entries in the ring, which always runs from
the most recent kill at the front to the oldest one still remembered.

  @kbd{M-y} can take a numeric argument, which tells it how many entries
to advance the ``last yank'' pointer by.  A negative argument moves the
pointer toward the front of the ring; from the front of the ring, it
moves ``around'' to the last entry and continues forward from there.

  Once the text you are looking for is brought into the buffer, you can
stop doing @kbd{M-y} commands and it will stay there.  It's just a copy
of the kill ring entry, so editing it in the buffer does not change
what's in the ring.  As long as no new killing is done, the ``last
yank'' pointer remains at the same place in the kill ring, so repeating
@kbd{C-y} will yank another copy of the same previous kill.

  If you know how many @kbd{M-y} commands it would take to find the
text you want, you can yank that text in one step using @kbd{C-y} with
a numeric argument.  @kbd{C-y} with an argument restores the text from
the specified kill ring entry, counting back from the most recent as
1.  Thus, @kbd{C-u 2 C-y} gets the next-to-the-last block of killed
text---it is equivalent to @kbd{C-y M-y}.  @kbd{C-y} with a numeric
argument starts counting from the ``last yank'' pointer, and sets the
``last yank'' pointer to the entry that it yanks.

@vindex kill-ring-max
  The length of the kill ring is controlled by the variable
@code{kill-ring-max}; no more than that many blocks of killed text are
saved.

@vindex kill-ring
  The actual contents of the kill ring are stored in a variable named
@code{kill-ring}; you can view the entire contents of the kill ring with
the command @kbd{C-h v kill-ring}.

@node Accumulating Text, Rectangles, Yanking, Top
@section Accumulating Text
@findex append-to-buffer
@findex prepend-to-buffer
@findex copy-to-buffer
@findex append-to-file

@cindex accumulating scattered text
  Usually we copy or move text by killing it and yanking it, but there
are other methods convenient for copying one block of text in many
places, or for copying many scattered blocks of text into one place.  To
copy one block to many places, store it in a register
(@pxref{Registers}).  Here we describe the commands to accumulate
scattered pieces of text into a buffer or into a file.

@table @kbd
@item M-x append-to-buffer
Append region to the contents of a specified buffer.
@item M-x prepend-to-buffer
Prepend region to the contents of a specified buffer.
@item M-x copy-to-buffer
Copy region into a specified buffer, deleting that buffer's old contents.
@item M-x insert-buffer
Insert the contents of a specified buffer into current buffer at point.
@item M-x append-to-file
Append region to the contents of a specified file, at the end.
@end table

  To accumulate text into a buffer, use @kbd{M-x append-to-buffer}.
This reads a buffer name, then inserts a copy of the region into the
buffer specified.  If you specify a nonexistent buffer,
@code{append-to-buffer} creates the buffer.  The text is inserted
wherever point is in that buffer.  If you have been using the buffer for
editing, the copied text goes into the middle of the text of the buffer,
starting from wherever point happens to be at that moment.

  Point in that buffer is left at the end of the copied text, so
successive uses of @code{append-to-buffer} accumulate the text in the
specified buffer in the same order as they were copied.  Strictly
speaking, @code{append-to-buffer} does not always append to the text
already in the buffer---it appends only if point in that buffer is at the end.
However, if @code{append-to-buffer} is the only command you use to alter
a buffer, then point is always at the end.

  @kbd{M-x prepend-to-buffer} is just like @code{append-to-buffer}
except that point in the other buffer is left before the copied text, so
successive prependings add text in reverse order.  @kbd{M-x
copy-to-buffer} is similar, except that any existing text in the other
buffer is deleted, so the buffer is left containing just the text newly
copied into it.

  To retrieve the accumulated text from another buffer, use the
command @kbd{M-x insert-buffer}; this too takes @var{buffername} as an
argument.  It inserts a copy of the whole text in buffer
@var{buffername} into the current buffer at point, and sets the mark
after the inserted text.  Alternatively, you can select the other
buffer for editing, then copy text from it by killing.
@xref{Buffers}, for background information on buffers.

  Instead of accumulating text within Emacs, in a buffer, you can append
text directly into a file with @kbd{M-x append-to-file}, which takes
@var{filename} as an argument.  It adds the text of the region to the end
of the specified file.  The file is changed immediately on disk.

  You should use @code{append-to-file} only with files that are
@emph{not} being visited in Emacs.  Using it on a file that you are
editing in Emacs would change the file behind Emacs's back, which
can lead to losing some of your editing.

@node Rectangles, Registers, Accumulating Text, Top
@section Rectangles
@cindex rectangle
@cindex columns (and rectangles)
@cindex killing rectangular areas of text

  The rectangle commands operate on rectangular areas of the text: all
the characters between a certain pair of columns, in a certain range of
lines.  Commands are provided to kill rectangles, yank killed rectangles,
clear them out, fill them with blanks or text, or delete them.  Rectangle
commands are useful with text in multicolumn formats, and for changing
text into or out of such formats.

  When you must specify a rectangle for a command to work on, you do it
by putting the mark at one corner and point at the opposite corner.  The
rectangle thus specified is called the @dfn{region-rectangle} because
you control it in much the same way as the region is controlled.  But
remember that a given combination of point and mark values can be
interpreted either as a region or as a rectangle, depending on the
command that uses them.

  If point and the mark are in the same column, the rectangle they
delimit is empty.  If they are in the same line, the rectangle is one
line high.  This asymmetry between lines and columns comes about
because point (and likewise the mark) is between two columns, but within
a line.

@table @kbd
@item C-x r k
Kill the text of the region-rectangle, saving its contents as the 
``last killed rectangle'' (@code{kill-rectangle}).
@item C-x r d
Delete the text of the region-rectangle (@code{delete-rectangle}).
@item C-x r y
Yank the last killed rectangle with its upper left corner at point
(@code{yank-rectangle}).
@item C-x r o
Insert blank space to fill the space of the region-rectangle
(@code{open-rectangle}).  This pushes the previous contents of the
region-rectangle rightward.
@item M-x clear-rectangle
Clear the region-rectangle by replacing its contents with spaces.
@item M-x delete-whitespace-rectangle
Delete whitespace in each of the lines on the specified rectangle,
starting from the left edge column of the rectangle.
@item C-x r t @var{string} @key{RET}
Replace rectangle contents with @var{string} on each line.
(@code{string-rectangle}).
@item M-x string-insert-rectangle @key{RET} @var{string} @key{RET}
Insert @var{string} on each line of the rectangle.
@end table

  The rectangle operations fall into two classes: commands for
deleting and inserting rectangles, and commands for blank rectangles.

@kindex C-x r k
@kindex C-x r d
@findex kill-rectangle
@findex delete-rectangle
  There are two ways to get rid of the text in a rectangle: you can
discard the text (delete it) or save it as the ``last killed''
rectangle.  The commands for these two ways are @kbd{C-x r d}
(@code{delete-rectangle}) and @kbd{C-x r k} (@code{kill-rectangle}).  In
either case, the portion of each line that falls inside the rectangle's
boundaries is deleted, causing any following text on the line to
move left into the gap.

  Note that ``killing'' a rectangle is not killing in the usual sense; the
rectangle is not stored in the kill ring, but in a special place that
can only record the most recent rectangle killed.  This is because yanking
a rectangle is so different from yanking linear text that different yank
commands have to be used and yank-popping is hard to make sense of.

@kindex C-x r y
@findex yank-rectangle
  To yank the last killed rectangle, type @kbd{C-x r y}
(@code{yank-rectangle}).  Yanking a rectangle is the opposite of killing
one.  Point specifies where to put the rectangle's upper left corner.
The rectangle's first line is inserted there, the rectangle's second
line is inserted at the same horizontal position, but one line
vertically down, and so on.  The number of lines affected is determined
by the height of the saved rectangle.

  You can convert single-column lists into double-column lists using
rectangle killing and yanking; kill the second half of the list as a
rectangle and then yank it beside the first line of the list.
@xref{Two-Column}, for another way to edit multi-column text.

  You can also copy rectangles into and out of registers with @kbd{C-x r
r @var{r}} and @kbd{C-x r i @var{r}}.  @xref{RegRect,,Rectangle
Registers}.

@kindex C-x r o
@findex open-rectangle
@findex clear-rectangle
  There are two commands you can use for making blank rectangles:
@kbd{M-x clear-rectangle} which blanks out existing text, and @kbd{C-x r
o} (@code{open-rectangle}) which inserts a blank rectangle.  Clearing a
rectangle is equivalent to deleting it and then inserting a blank
rectangle of the same size.

@findex delete-whitespace-rectangle
  The command @kbd{M-x delete-whitespace-rectangle} deletes horizontal
whitespace starting from a particular column.  This applies to each of
the lines in the rectangle, and the column is specified by the left
edge of the rectangle.  The right edge of the rectangle does not make
any difference to this command.

@kindex C-x r t
@findex string-rectangle
  The command @kbd{C-x r t} (@code{string-rectangle}) replaces the
contents of a region-rectangle with a string on each line.  The
string's width need not be the same as the width of the rectangle.  If
the string's width is less, the text after the rectangle shifts left;
if the string is wider than the rectangle, the text after the
rectangle shifts right.

@findex string-insert-rectangle
  The command @kbd{M-x string-insert-rectangle} is similar to 
@code{string-rectangle}, but inserts the string on each line, 
shifting the original text to the right.