let nextmonth=$curmonth+1
if [ "$nextmonth" -gt 12 ]; then
    nextmonth=1
    let pyear=$curyear+1
fi
#nextmonth="`printf '%.2d' $nextmonth`"

let prevmonth=$curmonth-1
if [ "$prevmonth" -lt 1 ]; then
    prevmonth=12
    let pyear=$curyear-1
fi