Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many help commands use this feature.
This function executes the forms in body while arranging to insert
any output they print into the buffer named buffer-name, which is
first created if necessary, and put into Help mode. (See the similar
form with-temp-buffer-window below.) Finally, the buffer is
displayed in some window, but that window is not selected.
If the forms in body do not change the major mode in the output
buffer, so that it is still Help mode at the end of their execution,
then with-output-to-temp-buffer makes this buffer read-only at
the end, and also scans it for function and variable names to make them
into clickable cross-references. See Tips for
Documentation Strings, in particular the item on hyperlinks in
documentation strings, for more details.
The string buffer-name specifies the temporary buffer, which need
not already exist. The argument must be a string, not a buffer. The
buffer is erased initially (with no questions asked), and it is marked
as unmodified after with-output-to-temp-buffer exits.
with-output-to-temp-buffer binds standard-output to the
temporary buffer, then it evaluates the forms in body. Output
using the Lisp output functions within body goes by default to
that buffer (but screen display and messages in the echo area, although
they are “output” in the general sense of the word, are not affected).
See Output Functions.
Several hooks are available for customizing the behavior of this construct; they are listed below.
The value of the last form in body is returned.
---------- Buffer: foo ---------- This is the contents of foo. ---------- Buffer: foo ----------
(with-output-to-temp-buffer "foo"
(print 20)
(print standard-output))
⇒ #<buffer foo>
---------- Buffer: foo ----------
20
#<buffer foo>
---------- Buffer: foo ----------
If this variable is non-nil, with-output-to-temp-buffer
calls it as a function to do the job of displaying a help buffer. The
function gets one argument, which is the buffer it should display.
It is a good idea for this function to run temp-buffer-show-hook
just as with-output-to-temp-buffer normally would, inside of
save-selected-window and with the chosen window and buffer
selected.
This normal hook is run by with-output-to-temp-buffer before
evaluating body. When the hook runs, the temporary buffer is
current. This hook is normally set up with a function to put the
buffer in Help mode.
This normal hook is run by with-output-to-temp-buffer after
displaying the temporary buffer. When the hook runs, the temporary buffer
is current, and the window it was displayed in is selected.
This macro is similar to with-output-to-temp-buffer. Like that
construct, it executes body while arranging to insert any output
it prints into the buffer named buffer-or-name and displays that
buffer in some window. Unlike with-output-to-temp-buffer,
however, it does not automatically switch that buffer to Help mode.
The argument buffer-or-name specifies the temporary buffer. It
can be either a buffer, which must already exist, or a string, in which
case a buffer of that name is created, if necessary. The buffer is
marked as unmodified and read-only when with-temp-buffer-window
exits.
This macro does not call temp-buffer-show-function. Rather, it
passes the action argument to display-buffer
(see Choosing a Window for Displaying a Buffer) in order to display the buffer.
The value of the last form in body is returned, unless the argument quit-function is specified. In that case, it is called with two arguments: the window showing the buffer and the result of body. The final return value is then whatever quit-function returns.
This macro uses the normal hooks temp-buffer-window-setup-hook
and temp-buffer-window-show-hook in place of the analogous hooks
run by with-output-to-temp-buffer.
The two constructs described next are mostly identical to
with-temp-buffer-window but differ from it as specified:
This macro is like with-temp-buffer-window but unlike that makes
the buffer specified by buffer-or-name current for running
body.
A window showing a temporary buffer can be fitted to the size of that buffer using the following mode:
When this minor mode is enabled, windows showing a temporary buffer are automatically resized to fit their buffer’s contents.
A window is resized if and only if it has been specially created for the
buffer. In particular, windows that have shown another buffer before
are not resized. By default, this mode uses fit-window-to-buffer
(see Resizing Windows) for resizing. You can specify a different
function by customizing the options temp-buffer-max-height and
temp-buffer-max-width below.
The effect of this option can be overridden by providing a suitable
window-height, window-width or window-size action
alist entry for display-buffer (see Action Alists for Buffer Display).
This option specifies the maximum height (in lines) of a window
displaying a temporary buffer when temp-buffer-resize-mode is
enabled. It can also be a function to be called to choose the height
for such a buffer. It gets one argument, the buffer, and should return
a positive integer. At the time the function is called, the window to
be resized is selected.
This option specifies the maximum width of a window (in columns)
displaying a temporary buffer when temp-buffer-resize-mode is
enabled. It can also be a function to be called to choose the width for
such a buffer. It gets one argument, the buffer, and should return a
positive integer. At the time the function is called, the window to be
resized is selected.
The following function uses the current buffer for temporary display:
This function momentarily displays string in the current buffer at position. It has no effect on the undo list or on the buffer’s modification status.
The momentary display remains until the next input event. If the next
input event is char, momentary-string-display ignores it
and returns. Otherwise, that event remains buffered for subsequent use
as input. Thus, typing char will simply remove the string from
the display, while typing (say) C-f will remove the string from
the display and later (presumably) move point forward. The argument
char is a space by default.
The return value of momentary-string-display is not meaningful.
If the string string does not contain control characters, you can
do the same job in a more general way by creating (and then subsequently
deleting) an overlay with a before-string property.
See Overlay Properties.
If message is non-nil, it is displayed in the echo area
while string is displayed in the buffer. If it is nil, a
default message says to type char to continue.
In this example, point is initially located at the beginning of the second line:
---------- Buffer: foo ---------- This is the contents of foo. ∗Second line. ---------- Buffer: foo ----------
(momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") ⇒ t
---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ----------