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| From: | Stefano Lattarini |
| Subject: | Re: [PATCH] docs: signal-related bugs and incompatibilities for the shells |
| Date: | Tue, 13 Sep 2011 19:50:51 +0200 |
| User-agent: | KMail/1.13.7 (Linux/2.6.30-2-686; KDE/4.6.5; i686; ; ) |
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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 <address@hidden> > > 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 <address@hidden> > > 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 > > address@hidden <http://lists.gnu.org/archive/html/bug-autoconf/2011-09/msg00004.html> > address@hidden Signal handling > address@hidden Signal handling > address@hidden Signal handling in the shell > address@hidden 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 > address@hidden://www.cons.org/cracauer/sigint.html, this article}. > + > +Solaris 10 @command{/bin/sh} automatically trap most signals by default; > address@hidden 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): > + > address@hidden > +$ @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 $?} > +> @kbd{done} > +signal 1: > +Hangup > +129 > +signal 2: > +208 > +signal 3: > +208 > +signal 15: > +208 > address@hidden example > + > +This gets even worse if one is using the POSIX `wait' interface to get > +details about the shell process terminations: it will result that the > +shell exited normally, not upon receiving a signal. > + > address@hidden > +$ @kbd{cat > foo.c <<'END'} > +#include <stdio.h> > +#include <stdlib.h> > +#include <sys/wait.h> > +int main(void) > address@hidden > + int status = system("kill -15 $$"); > + printf ("Terminated by signal: %s\n", > + WIFSIGNALED (status) ? "yes" : "no"); > + printf ("Exited normally: %s\n", > + WIFEXITED (status) ? "yes" : "no"); > + return 0; > address@hidden > +END > address@hidden $$ 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 > address@hidden 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 > address@hidden/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, $$'}, after > +the perl process has been interrupted AT&T @code{ksh93} (2011) will > +proceed to send itself a @code{SIGINT}, while Solaris 10 @code{/bin/ksh} > +and @code{/usr/xpg4/bin/sh} will proceed to exit with status 130 (i.e., > +128 + 2). In any case, if there is an active trap associated with > address@hidden, those shells will correctly execute it. > + > address@hidden Shell file descriptors > @node File System Conventions > @section File System Conventions > @cindex File system conventions > And consider this squashed in: diff --git a/doc/autoconf.texi b/doc/autoconf.texi index b71eb6d..dcdbe98 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -15570,12 +15570,12 @@ shell exited normally, not upon receiving a signal.
@example $ @kbd{cat > foo.c <<'END'} -#include <stdio.h> -#include <stdlib.h> -#include <sys/wait.h> +#include <stdio.h> /* for printf */ +#include <stdlib.h> /* for system */ +#include <sys/wait.h> /* for WIF* macros */ int main(void) @{ - int status = system("kill -15 $$"); + 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 |
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