Allow async command output buffer to be shown only on output

* lisp/simple.el (async-shell-command-display-buffer): Add
defcustom.
(shell-command): Use the new defcustom to determine whether to show
the buffer immediately, or add a process filter that shows it only
when there is some output.
* etc/NEWS: Document the new variable.
* doc/emacs/misc.texi: Likewise.

Thanks to Juri Linkov and Eli Zaretskii for advice and guidance.

1 files changed, 5 insertions, 0 deletions

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index 84681f2269a..73a6bae767a 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -742,6 +742,11 @@ this; e.g., whether to rename the pre-existing output buffer, or to
 use a different buffer for the new command.  Consult the variable's
 documentation for more possibilities.
 
+@vindex async-shell-command-display-buffer
+  If you want the output buffer for asynchronous shell commands to be
+displayed only when the command generates output, set
+@code{async-shell-command-display-buffer} to @code{nil}.
+
 @kindex M-|
 @findex shell-command-on-region
   @kbd{M-|} (@code{shell-command-on-region}) is like @kbd{M-!}, but