make bash script wait for a signal using and empty named pipe

Question

I'm trying to make a bash script wait for a signal using and empty named pipe. I like this approach most than:

while : ; do sleep 1 ; done

because it's a kind of busy-waiting

I try:

trap 'echo SIGNAL!' INT
while true;
do
  read
  echo 'AFTER READ'
done < /tmp/fifo

where /tmp/fifo is the empty named pipe

and I get:

bash: /tmp/fifo: Interrupted system call
SIGNAL!

bash script aborts. How can I make the script keep looping when receiving the signal? Thanks

If you just want the script to pause itself, have it send itself `SIGSTOP`; later, when you are ready for it to resume, send it `SIGCONT`. This doesn't require any special handling on the part of the script itself. — chepner, Dec 04 '13 at 19:12
Nope, since script has been stopped, it doesn't react to signals sent to him, p.e. SIGINT — francesc, Dec 04 '13 at 19:19

score 3 · Accepted Answer · edited May 23 '17 at 11:43

3

To expand on this answer:

trap 'echo SIGNAL!; kill $(jobs -p)' INT
read < /tmp/fifo &
wait

edited May 23 '17 at 11:43

Community

answered Dec 04 '13 at 19:24

chepner

ok, that works, I just didn't want to create an additional proces – francesc Dec 04 '13 at 19:31
This is just a single `fork`, so the overhead is fairly minimal. – chepner Dec 04 '13 at 19:41
+1 for not neglecting your children, which the original answer did. Unfortunately, this litters my console with ugly "Terminated signal 15" warnings. Perhaps `sh -c 'trap "exit 0" TERM; read < /tmp/fifo' &` ? Or `perl -e '$SIG{TERM}=\&exit; sleep'` ? – pilcrow Dec 04 '13 at 20:03
@pilcrow I think those are produced by the shell's job control feature, which is only active in an interactive shell. – chepner Dec 04 '13 at 20:25
ok,.. I see now the alternatives. I think we can conclude there are ways in shell scripting, but not as straightforward as in C, with pause() (or sigwaitinfo() for that matter) – francesc Dec 04 '13 at 20:57

1 Answers1