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 c...@case.edu http://tiswww.cwru.edu/~chet/
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