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Re: trap - inconsistent behaviour

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On 9/20/18 7:39 PM, Jeremy Townshend wrote:

> Bash Version: 4.4
> Patch Level: 19
> Release Status: release
> 
> Description:
> 	The behaviour of the "trap" builtin command changes merely by printing the
> 	list of commands associated with each signal (trap command issued without
> 	arguments).
> 
> Repeat-By:
> 	Case 1: In a fresh terminal emulator issue the following:
> 
> 	( trap 'echo trapped >&2' HUP; { sleep 10 & sleepPID=$!; wait $sleepPID; } > >( sleep 1; kill -HUP $BASHPID; cat ) )
> 
> 	Case 2: Then in a fresh terminal emulator issue the following:
> 
> 	( trap 'echo trapped >&2' HUP; { sleep 10 & sleepPID=$!; wait $sleepPID; } > >( trap; sleep 1; kill -HUP $BASHPID; cat ) )
> 
> 	Expected outcome: either the trap is triggered in both cases or in neither
> 	since the only difference is the additional trap command with no arguments
> 	(for printing the list of commands associated with each signal).  That is, in
> 	this case, "trapped" is expected to be printed in both cases or in neither
> 	case.

The trap command shouldn't be executed in either case. The process
substitution is executed in a subshell environment, which doesn't inherit
traps from its parent (though it inherits the trap strings; see
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_28).

The process substitution sends the SIGHUP to itself ($BASHPID), which
should cause it to terminate but not result in a signal being sent to its
parent. However, the parent is getting a SIGHUP from somewhere.

It seems like this behavior is the result of the shell being interactive.
I'll take a look.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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Re: trap - inconsistent behaviour Chet Ramey <chet.ramey@case.edu> - 2018-09-21 08:17 -0400

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