previousruntime=0
while :
do
#echo "start";
#echo "start-time: $(date)"
#today="$(date +%s)"
today=`date -d @$(( $(date +"%s") - 20 )) +%s`
if [ $previousruntime == 0 ];
then
   echo " assign " $previousruntime
    previousruntime=$today
    echo "assign"
fi

echo "CurrentEpoch:" $today
echo "Previoustime:" $previousruntime
echo /usr/bin/php /var/www/html/SmartCity/PushData.php $today $previousruntime 
/usr/bin/php /var/www/html/SmartCity/PushData.php $today $previousruntime &

 previousruntime=$today
#echo "end";
sleep 20
done