Script that takes screenshot every minute

#!/bin/bash
# script to run screencapture every one second

screenshot="$(which screencapture) -x -m -C"
freq=60		#take a screenshot every 30 seconds
maxshots=100000000000	#take 45 screenshots then quit


while getopts "af:m" opt; do
	case $opt in
	f ) freq=$OPTARG;		;;
	m ) maxshots=$OPTARG;	;;
	? ) echo "Usage: $0 [-f frequency] [-m maxcaps]" >&2
		exit 1
	esac
done
sleep 60
counter=1 	#set startng number; incrementally append to filename

while [ $counter -le $maxshots ] ; do
	da=`date +"%d:%m:%y-%H:%M"`
	echo "done ${counter} date is : ${da}"
	$screenshot "(${counter})${da}".jpg
	counter=$(( counter + 1 ))
	sleep $freq
done

exit