su - run a command with substitute user and group ID

su command without any option $ su

su command to make the shell a login shell $ su - user3

To switch to root user $ su -

To print help options $ su -h

To switch to a Different User $ su -l user3

To Use su with sudo command $ sudo su - user3

To run specific command as a different user $ su -c pwd user3

To use a different shell $ su -s /usr/bin/csh

To Execute a command as different user with su command $ su -c <command> user3

To use a different user in the same environment $ su -p user3 $ su -m user3

regards, T.Dhanasekar