timeout: add --foreground to support interactive commands

Or more accurately, commands not started from the shell prompt,
that are interactive, or need to receive Ctrl-C etc. from the terminal.

* doc/coreutils.texi (timeout invocation): Document --foreground.
* src/timeout.c (main): Set the foreground flag and don't create
a separate group.
(cleanup): Only send a signal directly to the monitored command
when the foreground flag is set.
(usage): Describe --foreground.
* tests/misc/timeout-group: Add a new test.
* tests/Makefile.am: Reference new test.
NEWS: Mention the new option.

Reported by Shay Shimony
Analysis by Alan Curry
Fix suggested by Paul Eggert

1 files changed, 17 insertions, 0 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 1ab8a92e9..424446c25 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -15658,6 +15658,23 @@ The program accepts the following options.  Also see @ref{Common options}.
 Options must precede operands.
 
 @table @samp
+@itemx --foreground
+@opindex --foreground
+Don't create a separate background program group, so that
+the managed @var{command} can use the foreground TTY normally.
+This is needed to support timing out commands not started
+directly from an interactive shell, in two situations.
+@enumerate
+@item
+@var{command} is interactive and needs to read from the terminal for example
+@item
+the user wants to support sending signals directly to @var{command}
+from the terminal (like Ctrl-C for example)
+@end enumerate
+
+Note in this mode of operation, any children of @var{command}
+will not be timed out.
+
 @item -k @var{duration}
 @itemx --kill-after=@var{duration}
 @opindex -k