Thread: Interval processing script, interesting problem...

Hi

I need to execute a function on set intervals, in seconds.
Came up with this:

Code:

#!/bin/bash
INTERVAL=2
while true; do
	SECOND=`date +"%S"`
	(($SECOND % $INTERVAL)) || echo "execute on second: $SECOND"
	sleep 1	
done

Basically execution should happen if the current second mod the interval is equal to zero.

Sample output:
execute on second: 00
execute on second: 02
execute on second: 04
execute on second: 06
./timer.sh: line 4: ((: 08: value too great for base (error token is "08")
execute on second: 08
./timer.sh: line 4: ((: 09: value too great for base (error token is "09")
execute on second: 09
execute on second: 10
execute on second: 12
execute on second: 14
execute on second: 16
execute on second: 18
execute on second: 20
execute on second: 22
execute on second: 24

Anybody knows what is happening there on second 8 and 9?

Tested on CentOs and OSX.

Seconds is 01, 02 ,03 etc...

Apparently when a number has a leading zero, c sees it as an octal number.

This is the fix:

Code:

#!/bin/bash
INTERVAL=2
while true; do
	SECOND=`date +"%S"`
	((10#$SECOND % $INTERVAL)) || echo "execute on second: $SECOND"
	sleep 1	
done

That tells bash that seconds is base 10

Cheers.