It's enough to do:
data=`date`
datatime=`date -d "${data}" '+%Y%m%d'`
echo $datatime
20190206
If you want to add also the time you can use in that way
data=`date`
datatime=`date -d "${data}" '+%Y%m%d %T'`
echo $data
Wed Feb 6 03:57:15 EST 2019
echo $datatime
20190206 03:57:15