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sleep command off by a second


 
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# 1  
Question sleep command off by a second

Hi Forum
Im using sleep in a while loop goes around 10 times. i feed it a variable with the time i what it to sleep for eg sleep $sleepVal and then print system date and time to screen but sometimes 1 second is added to the time why is this
here my code

Code:
sleepVal=5

 while [ ${counter} -le 10 ]
    do
     printf "%d) %s\n" ${counter} `date +%d-%m-%Y:%R-%S` 
     sleep ${sleepVal}
     counter=`expr ${counter} + 1`
    done

Smilie
any help would be much appreciated and thank you in advance
# 2  
Your loop contains, in this case, a sleep 5 command. The rest of the loop also requires a little bit of time to run. This is especially true if the OS has another program (like cron) that suddenly starts to run. If you start your script near the beginning of a second you might have enough excess milliseconds to handle everything else. But if you start the loop toward the end of a second that might not be true.
# 3  
expr is also very inefficient (if every millisecond is a prisoner Smilie).

Code:
$ cat exprTest
count=1000

counter=0
printf "With expr, Start: "
date
while [ $counter -le $count ]; do
  counter=`expr $counter + 1`
done
printf "With expr, End:   "
date
echo $counter

counter=0
printf "Without expr, Start: "
date
while [ $counter -le $count ]; do
  ((counter++))
done
printf "Without expr, End:   "
date
echo $counter


$ ./exprTest
With expr, Start: Mon  4 Apr 2011 22:13:59 CEST
With expr, End:   Mon  4 Apr 2011 22:14:01 CEST
1001
Without expr, Start: Mon  4 Apr 2011 22:14:01 CEST
Without expr, End:   Mon  4 Apr 2011 22:14:01 CEST
1001

# 4  
sorry for the late reply guys been busy cheers for the anwsersSmilie
 

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