Date: Wed, 17 Apr 2019 11:35:18 +0200
From: Joerg Schilling <joerg.schill...@fokus.fraunhofer.de>
Message-ID: <5cb6f356.dh4k5z2xfkptm0+v%joerg.schill...@fokus.fraunhofer.de>
| If the standard did require something that is neither covered by the
| historical Bourne Shell behavior
We know the historical Bourne shell output the trap that was set
by the user, regardless of whether that resulted in a signal being
caught, or not because the signal was ignored on entry to the shell.
I showed the code that did that in an earlier message.
| nor ksh88
I don't have access to ksh88 to test it, but something tells me that
if it did what it is claimed the standard requires, we would have been
told about it by now.
ksh93 doesn't...
ksh93 $ (trap '' INT EMT; ksh93 -c trap)
ksh93 $
What ksh93 does do however, is that if an attempt is made to
trap a signal, and that doesn't result in changing the signal
disposition, then after that the trap command tells you the
signal is ignored...
ksh93 $ (trap '' INT EMT; ksh93 -c 'trap "echo foo" INT; trap')
trap -- '' INT
ksh93 $
But that only happens if a trap action is set (or, obviously, if the
script requests to ignore the signal)
If the script requests to reset the signal to default, we're back
to no output
ksh93 $ (trap '' INT EMT; ksh93 -c 'trap - INT; trap')
ksh93 $
That is, unless it was first set to some other state:
ksh93 $ (trap '' INT EMT; ksh93 -c 'trap "" INT; trap - INT; trap')
trap -- '' INT
ksh93 $ (trap '' INT EMT; ksh93 -c 'trap "echo foo" INT; trap - INT; trap')
trap -- '' INT
All that mess just looks like bugs in ksh93 to me...
yash and bosh seem to completely ignore any attempt to trap a signal
that's ignored at startup (in a non-interactive shell - all these tests
test non-interactive shells).
bosh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap - INT; trap')
bosh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap')
bosh $ (trap '' INT EMT; $SHELL -c 'trap "echo foo" INT; trap')
bosh $
(if the signal was not inored, the right thing happens)
yash $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap - INT; trap')
yash $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap')
yash $ (trap '' INT EMT; $SHELL -c 'trap "echo foo" INT; trap')
yash $
old pdksh and mksh both do ...
mksh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap - INT; trap')
mksh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap')
trap -- INT
mksh $ (trap '' INT EMT; $SHELL -c 'trap "echo foo" INT; trap')
trap -- 'echo foo' INT
mksh $
Pity about the lack of quoting around the null string action in the
middle example ... but if I was forced to guess, I'd tend to assume
that ksh88 probably acts that way as well (perhaps even including the
missing explicit null string).
I am not sure what happens exactly with zsh (what is going on) I don't
usually use it, and don't understand all of its variations, but in that
one I need to send an extra newline, otherwise it simply sits and waits
forever... But with that newline:
zsh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap - INT; trap')
zsh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap')
trap -- '' INT
zsh $ (trap '' INT EMT; $SHELL -c 'trap "echo foo" INT; trap')
trap -- 'echo foo' INT
zsh $
The shell I generally regard as the most standards conforming of all
I have seen (certainly more than its close relative, the NetBSD sh)
that is, the FreeBSD shell (it seems like any time they find anytging
that is different than the standard requires, they change it) does
fbsh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap - INT; trap')
fbsh $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap')
trap -- '' INT
fbsh $ (trap '' INT EMT; $SHELL -c 'trap "echo foo" INT; trap')
trap -- 'echo foo' INT
fbsh $
bash is the one that is notably different...
bash $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap - INT; trap')
trap -- '' SIGINT
trap -- '' SIGEMT
bash $ (trap '' INT EMT; $SHELL -c 'trap "" INT; trap')
trap -- '' SIGINT
trap -- '' SIGEMT
bash $ (trap '' INT EMT; $SHELL -c 'trap "echo foo" INT; trap')
trap -- '' SIGINT
trap -- '' SIGEMT
bash $
(In each of these, $SHELL is the shell indicated by the PS1 output).
kre
