Check backup

#!/bin/bash

test "$#" -lt 1 &&  { echo "no option found" ; exit 2 ; }
function isanumber()
{
WERT=$(echo $1 | grep "^[0-9]\+$")
if [ "x$WERT" != "x" ]
then
return 0
else
return 1
fi
}
while getopts h:b: opt
do
   case $opt in
       #b) echo "Option b";;
       h) HOURS=$OPTARG;;
       b) BACKUP=$OPTARG;;
        ?) echo "USAGE: $0 -h HOURS -b BACKUP"; exit 2 ;;
   esac
done
isanumber $HOURS || { echo "HOUR must be a INTEGER" ; exit 2 ; }
test -d $BACKUP || { echo "no backup dir found" ; exit 2 ; }
DAT=$(ls -rt $BACKUP/* | tail -1)
DATHOURS=$(($(stat -c %X $DAT)/3600))
NOW=$(($(date "+%s")/3600))
DIFF=$(($NOW - $DATHOURS))
NEXT=$(($HOURS - $DIFF))
OVER=$(($DIFF - $HOURS))
test $DIFF -gt $HOURS && { echo "backup is missing since $OVER h" ; exit 2 ;}
BASE=$(basename $DAT)
MES=$(echo $BASE | cut -f 1 -d .)
ERR=$(echo $BASE | cut -f 2 -d .)
if test "$ERR" -eq "0"
then
FLAG="is ok - next in $NEXT h"
else
FLAG="is not ok"
fi
#echo "BACKUP from $MES $FLAG" 
echo "BACKUP $FLAG" 
exit $ERR