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
– chepner, Commented Dec 4, 2013 at 19:12
Nope, since script has been stopped, it doesn't react to signals sent to him, p.e. SIGINT — francesc
– francesc, Commented Dec 4, 2013 at 19:19

Community · Accepted Answer · 2017-05-23 11:43:54Z

3

To expand on this answer:

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

edited May 23, 2017 at 11:43

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answered Dec 4, 2013 at 19:24

chepner

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5 Comments

francesc Over a year ago

ok, that works, I just didn't want to create an additional proces

chepner Over a year ago

This is just a single fork, so the overhead is fairly minimal.

pilcrow Over a year ago

+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' ?

chepner Over a year ago

@pilcrow I think those are produced by the shell's job control feature, which is only active in an interactive shell.

francesc Over a year ago

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)

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