kill – Ryan Schulze

Bash scripting, traps and sleep

October 9, 2009March 12, 2011Ryan1 Commentbackground, bash, kill, trap

Today I ran into any old problem: you have a script that should do something when it recieves a signal (e.g. if someone sends it USR1 it should write to a log/syslog), but the script uses a long sleep because it normally only checks/calculates stuff every x min. If you send it a kill -USR1 $pid it will normally execute the trap AFTER the sleep is done, not so great. I figured of the following solution today: put the sleep in a while loop that checks if the full time was slept, and inside the loop a sleep that sleeps the X seconds remaing in the background followed by a wait.

If the script now recieves a USR1 it can kill the wait, execute the trap and will continue the remaining sleep on the next iteration of the loop.

#!/bin/bash

initialize() {
set -o nounset
trap cleanup INT TERM EXIT
trap print_foo USR1
}

cleanup() {
exit 0
}

print_foo() {
echo "foo"
}

initialize

# sleep 1 min
SLEEPTILL=$(date '+%s' --date="+1 min")

while [[ $(date '+%s') -lt ${SLEEPTILL} ]]
do
sleep $(bc &lt;&lt;&lt; "${SLEEPTILL} - $(date '+%s')") &amp;
BACKGROUND=$!
wait $BACKGROUND
done

#!/bin/bash

initialize() {

set -o nounset

trap cleanup INT TERM EXIT

trap print_foo USR1

}

cleanup() {

exit 0

}

print_foo() {

echo "foo"

}

initialize

# sleep 1 min

SLEEPTILL=$(date '+%s' --date="+1 min")

while [[ $(date '+%s') -lt ${SLEEPTILL} ]]

sleep $(bc <<< "${SLEEPTILL} - $(date '+%s')") &

BACKGROUND=$!

wait $BACKGROUND

done