Right way install rpm via alien:
alien -i my_rpm_name.rpm
If alien is not installed:
sudo apt-get install alien
error: Failed dependencies:/bin/sh is needed by XXX
This happens because bash rpm is not available in the new rpmdb path. You would have to use following to get the rpm installed.
# rpm --dbpath $HOME/myrpmdb --nodeps -ivh XXX.rpm
Because you've told it to use a completely different database, rpm doesn't look at the system database which is where /bin/sh would be found.
/bin/sh