how can I change SLEEP time in a running bash script

Question

Appendix: the code below runs fine, as Matthias pointed out. The err happened at another place. In short: if you want that sleep is changed during script runtime, e.g. due to a certain event, you might use the code below.

Original description:

My bash script ought to check a certain status - e.g. the existence of a file - every 5 minutes. If the status is as expected, everything is fine. But if the status is otherwise, the checks ought to happen in a shorter frequency, until everything is normal again.

Example:

NORMAL_SLEEP=300
SHORT_SLEEP=30
CUR_SLEEP=''

while :
do

if [ -f /tmp/myfile ]; then
    logger "myfile still exists. Next check in 5min"
    CUR_SLEEP=$NORMAL_SLEEP
else
     logger "myfile disappeared. Check again in 30s!"
     CUR_SLEEP=$SHORT_SLEEP
     echo "/tmp/myfile was removed. Check this!" \
     | mailx -s "alert: myfile missed" johndoe@somewhere.com
fi

trap 'kill $SLEEP_PID; exit 1' 15
sleep $CUR_SLEEP &
SLEEP_PID=$!
wait

done

Problem: the sleep time does not adapt...

Had a look at Bash Script: While-Loop Subshell Dilemma but unfortunately can't see how it could solve my problem.

Possible duplicate of [Bash Script: While-Loop Subshell Dilemma](http://stackoverflow.com/questions/13726764/bash-script-while-loop-subshell-dilemma) — Aaron, Mar 01 '17 at 13:32
Which sleep length is it stuck on, if it does not adapt? Also, do the messages change - which ones come out? — Mark Setchell, Mar 01 '17 at 13:34
@MarkSetchell sleep stays at default 300s/5min; messages are correct because the missing file is recognised, but the intended change of sleep does not happen. Checks keep running every 5mins. — MarkHelms, Mar 01 '17 at 13:46
@chepner agreed, but the post presented the code as an example, so I thought it might be worth a shot. I should just have linked the question rather than tagged as duplicate though. — Aaron, Mar 01 '17 at 13:59
@Aaron is it possible to remove the duplicate tag? Thanks for your support, anyway! — MarkHelms, Mar 01 '17 at 15:29
@MarkHelms sure, removed ; technically the question should be closed as the error couldn't be reproduced with the posted code though, the reasoning being that it won't help people checking it. — Aaron, Mar 01 '17 at 18:49

score 1 · Accepted Answer · answered Mar 01 '17 at 14:19

The code ran fine on my machine. Here's what I ran (changed the time values just to test):

./script.sh --> "myfile disappeared. Check again in 30s!" printed at 2 sec intervals
touch /tmp/myfile
./script.sh --> "myfile still exists. Next check in 5min" printed at 5 sec intervals

The file, script.sh:

#!/bin/bash

NORMAL_SLEEP=5
SHORT_SLEEP=2
CUR_SLEEP=''

while :
do

if [ -f /tmp/myfile ]; then
    echo "myfile still exists. Next check in 5min"
    CUR_SLEEP=$NORMAL_SLEEP
else
     echo "myfile disappeared. Check again in 30s!"
     CUR_SLEEP=$SHORT_SLEEP
     echo "/tmp/myfile was removed. Check this!" \
     | mailx -s "alert: myfile missed" johndoe@somewhere.com
fi

trap 'kill $SLEEP_PID; exit 1' 15
sleep $CUR_SLEEP &
SLEEP_PID=$!
wait

done

And I probably sent some mail to johndoe@somewhere.com but that's okay.

Yes, you are right! I had a glitch further down my script, where I evaluated a variable falsely and thus reset the sleep to default (not to see in the example above). Sorry. — MarkHelms, Mar 01 '17 at 15:24

how can I change SLEEP time in a running bash script

1 Answers1