Allow not erase output buffer in shell commands

* lisp/simple.el (shell-command-not-erase-buffer): New option to allow
not erasing the output buffer between shell commands.  Defaults to nil.
(shell-command-on-region): Use it.
(shell-command--save-pos-or-erase): New defun; store a buffer position
if 'shell-command-not-erase-buffer' is non-nil; otherwise
erase the output buffer of the shell command.
(shell-command, shell-command-on-region): Use it.
(shell-command--set-point-after-cmd): New defun;
if 'shell-command-not-erase-buffer' is non-nil, set point
in the output buffer to the position in 'shell-command-saved-pos'.
(shell-command-sentinel, shell-command-on-region): Use it.
* doc/emacs/misc.texi (shell-command-not-erase-buffer):
Document this feature in the manual.
; * etc/NEWS: Add entry for this new feature.
See discussion on:
http://lists.gnu.org/archive/html/emacs-devel/2016-07/msg00610.html

1 files changed, 10 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index d62dcacbe98..8a13d525450 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -56,6 +56,16 @@ affected by this, as SGI stopped supporting IRIX in December 2013.
 * Changes in Emacs 25.2
 
 +++
+** The new user option 'shell-command-not-erase-buffer' controls
+if the output buffer is erased between shell commands; if non-nil,
+the output buffer is not erased; this variable also controls where
+to set the point in the output buffer: beginning of the output,
+end of the buffer or save the point.
+When 'shell-command-not-erase-buffer' is nil, the default value,
+the behaviour of 'shell-command', 'shell-command-on-region' and
+'async-shell-command' is as usual.
+
++++
 ** The new user option 'mouse-select-region-move-to-beginning'
 controls the position of point when double-clicking mouse-1 on the end
 of a parenthetical grouping or string-delimiter: the default value nil