[Toybox] Confused by bash trap handler return value.

[Chet Ramey]

On 2/10/25 7:25 PM, Rob Landley wrote:
> I don't understand how to reconcile the behavior of all three of these in 
> debian's bash 5.2.15(1):

Trap actions have no "return value." POSIX says:

"The value of "$?" after the trap action completes shall be the value it
had before the trap action was executed."

> 
> $ bash -c $'trap \'echo hello;false\' USR1 && kill -s USR1 $$ && echo here $?'
> hello
> here 0
> $ bash -c $'trap \'echo hello;false\' USR1 && kill -s USR1 9876543; echo 
> here $?'
> bash: line 1: kill: (9876543) - No such process
> here 1
> $ bash -c $'trap \'echo hello;false\' USR1 && kill -s USR1 $$ 9876543; echo 
> here $?'
> bash: line 1: kill: (9876543) - No such process
> hello
> here 0
> 
> 1) The previous statement returns 0 but the trap handler returns 1, so the 
> next statement sees zero.

Executing a trap action doesn't change $?.

> 2) The previous statement returns 1, the trap handler doesn't run, so the 
> next statement sees 1.

As if the trap were not there at all.

> 3) The previous statement returns 1 and the trap handler returns 1, so the 
> next statement sees zero...?

The AND-OR list returns 0, since the trap command succeeds, the kill
command runs, and kill returns 0 if it sends at least one signal
successfully. That is documented:

"kill returns true if at least one signal was successfully  sent,
  or false if an error occurs or an invalid option is encountered."

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