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, 8 insertions, 0 deletions

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index 94e1f198f2..acddb7a8f7 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -771,6 +771,14 @@ the output buffer.  But if you change the value of the variable
 @code{shell-command-default-error-buffer} to a string, error output is
 inserted into a buffer of that name.
 
+@vindex shell-command-not-erase-buffer
+  By default, the output buffer is erased between shell commands.
+If you change the value of the variable
+@code{shell-command-not-erase-buffer} to a non-@code{nil} value,
+the output buffer is not erased.  This variable also controls where to
+set the point in the output buffer after the command completes; see the
+documentation of the variable for details.
+
 @node Interactive Shell
 @subsection Interactive Subshell