See below ....

$vi a.sh
ab=$(pwd)
echo " "
echo "Current working directory is $ab"
FILE=$(basename $ab)
echo "FILE returns $FILE "
echo " "
ab=$(pwd)
echo "Current working directory is $ab"
BANK=$(dirname $ab)
echo "BANK returns $BANK"
echo " "

INFILE=${FILE}.${BANK}.$$
echo $INFILE


dam@athena:~$ ./a.sh

Current working directory is /home/dam
FILE returns dam

Current working directory is /home/dam
BANK returns /home

dam./home.11937




Not sure what you are trying to achieve...

I think what you probably wanted was

/home/dam.11937