On Tuesday 13 September 2011, Stefano Lattarini wrote:
> * doc/autoconf.texi (Signal handling): New paragraph.
> (@menu at "Portable Shell", @detailmenu): Update.
>
> Motivated by recent discussion on the bug-autoconf list, as well
> as work in the automake testsuite:
> <https://lists.gnu.org/archive/html/bug-autoconf/2011-09/msg00003.html>
> <https://lists.gnu.org/archive/html/bug-autoconf/2011-09/msg00004.html>
> <http://lists.gnu.org/archive/html/automake-patches/2011-09/msg00066.html>
> ---
> ChangeLog | 7 ++++
> doc/autoconf.texi | 94
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 101 insertions(+), 0 deletions(-)
>
> diff --git a/ChangeLog b/ChangeLog
> index ab74303..e122686 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,6 +1,13 @@
> 2011-09-13 Stefano Lattarini <[email protected]>
>
> docs: signal-related bugs and incompatibilities for the shells
> + Motivated by recent discussion on the bug-autoconf list, as well
> + as work in the automake testsuite:
> + <https://lists.gnu.org/archive/html/bug-autoconf/2011-09/msg00003.html>
> + <https://lists.gnu.org/archive/html/bug-autoconf/2011-09/msg00004.html>
> +
> <http://lists.gnu.org/archive/html/automake-patches/2011-09/msg00066.html>
> + * doc/autoconf.texi (Signal handling): New paragraph.
> + (@menu at "Portable Shell", @detailmenu): Update.
>
> 2011-08-16 Stefano Lattarini <[email protected]>
>
> diff --git a/doc/autoconf.texi b/doc/autoconf.texi
> index 3377afe..b71eb6d 100644
> --- a/doc/autoconf.texi
> +++ b/doc/autoconf.texi
> @@ -509,6 +509,7 @@ Portable Shell Programming
> * Shellology:: A zoology of shells
> * Here-Documents:: Quirks and tricks
> * File Descriptors:: FDs and redirections
> +* Signal handling:: Shells, signals, and headaches
> * File System Conventions:: File names
> * Shell Pattern Matching:: Pattern matching
> * Shell Substitutions:: Variable and command expansions
> @@ -15070,6 +15071,7 @@ subset described above, is fairly portable nowadays.
> Also please see
> * Shellology:: A zoology of shells
> * Here-Documents:: Quirks and tricks
> * File Descriptors:: FDs and redirections
> +* Signal handling:: Shells, signals, and headaches
> * File System Conventions:: File names
> * Shell Pattern Matching:: Pattern matching
> * Shell Substitutions:: Variable and command expansions
> @@ -15521,6 +15523,98 @@ ksh[1]: exec: 10: not found
> 127
> @end example
>
> +@c <http://lists.gnu.org/archive/html/bug-autoconf/2011-09/msg00004.html>
> +@node Signal handling
> +@section Signal handling
> +@cindex Signal handling in the shell
> +@cindex Signals, shells and
> +
> +Portable handling of signals within the shell is another major source of
> +headaches. This is worsened by the fact that various different, mutually
> +incompatible approaches are possible in this area, each with its
> +distinctive merits and demerits. A detailed description of these possible
> +approaches, as well as of their the pros and cons, can be found in
> +@uref{http://www.cons.org/cracauer/sigint.html, this article}.
> +
> +Solaris 10 @command{/bin/sh} automatically trap most signals by default;
> +@c See: <http://dbaspot.com/shell/396118-bourne-shell-exit-code-term.html>
> +the shell still exits with error upon termination by one of those signals,
> +but in such a case the exit status might be somewhat unexpected (even if
> +allowed by POSIX, strictly speaking):
> +
> +@example
> +$ @kbd{bash -c 'kill -1 $$'; echo $?} # Will exit 128 + (signal number).
> +Hangup
> +129
> +$ @kbd{/bin/ksh -c 'kill -15 $$'; echo $?} # Likewise.
> +Terminated
> +143
> +$ @kbd{for sig in 1 2 3 15; do}
> +> @kbd{ echo $sig:}
> +> @kbd{ /bin/sh -c "kill -$s \$\$"; echo $?}
> +> @kbd{done}
> +signal 1:
> +Hangup
> +129
> +signal 2:
> +208
> +signal 3:
> +208
> +signal 15:
> +208
> +@end example
> +
> +This gets even worse if one is using the POSIX `wait' interface to get
> +details about the shell process terminations: it will result that the
> +shell exited normally, not upon receiving a signal.
> +
> +@example
> +$ @kbd{cat > foo.c <<'END'}
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/wait.h>
> +int main(void)
> +@{
> + int status = system("kill -15 $$");
> + printf ("Terminated by signal: %s\n",
> + WIFSIGNALED (status) ? "yes" : "no");
> + printf ("Exited normally: %s\n",
> + WIFEXITED (status) ? "yes" : "no");
> + return 0;
> +@}
> +END
> +@c $$ font-lock
> +$ @kbd{cc -o foo foo.c}
> +$ @kbd{./a.out} # On GNU/Linux
> +Terminated by signal: no
> +Exited normally: yes
> +$ @kbd{./a.out} # On Solaris 10
> +Terminated by signal: yes
> +Exited normally: no
> +@end example
> +
> +Some shells seem to handle @code{SIGQUIT} specially: they ignore it even
> +if it is not blocked, and even if the shell is not running interactively
> +(in fact, even if the shell has no attached tty); among these shells
> +are at least Bash (from version 2 onwards), Zsh 4.3.12, Solaris 10
> +@code{/bin/ksh} and @code{/usr/xpg4/bin/sh}, and AT&T @code{ksh93} (2011).
> +Still, @code{SIGQUIT} seems to be trappable quite portably within all
> +these shells. OTOH, some other shells doesn't special-case the handling
> +of @code{SIGQUIT}; among these shells are at least @code{pdksh} 5.2.14,
> +Solaris 10 and NetBSD 5.1 @code{/bin/sh}, and the Almquist Shell 0.5.5.1.
> +
> +Some shells (especially Korn shells and derivatives) might try to
> +propagate to themselves a signal that has killed a child process; this is
> +not a bug, but a conscious design choice (although its overall value might
> +be debatable). The exact details of how this is attained vary from shell
> +to shell. For example, upon running @code{perl -e 'kill 2, $$'}, after
> +the perl process has been interrupted AT&T @code{ksh93} (2011) will
> +proceed to send itself a @code{SIGINT}, while Solaris 10 @code{/bin/ksh}
> +and @code{/usr/xpg4/bin/sh} will proceed to exit with status 130 (i.e.,
> +128 + 2). In any case, if there is an active trap associated with
> +@code{SIGINT}, those shells will correctly execute it.
> +
> +@cindex Shell file descriptors
> @node File System Conventions
> @section File System Conventions
> @cindex File system conventions
>
And consider this squashed in:
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index b71eb6d..dcdbe98 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -15570,12 +15570,12 @@ shell exited normally, not upon receiving a signal.
@example
$ @kbd{cat > foo.c <<'END'}
-#include <stdio.h>
-#include <stdlib.h>
-#include <sys/wait.h>
+#include <stdio.h> /* for printf */
+#include <stdlib.h> /* for system */
+#include <sys/wait.h> /* for WIF* macros */
int main(void)
@{
- int status = system("kill -15 $$");
+ int status = system ("kill -15 $$");
printf ("Terminated by signal: %s\n",
WIFSIGNALED (status) ? "yes" : "no");
printf ("Exited normally: %s\n",
Sorry for the noise,
Stefano
