su : run a command with substitute user
[SYNOPSIS] su [-] USER
OPTION
-m, -p do not reset environment variables
-w LIST don't reset specified variables
-g GROUP specify the primary group
-G GROUP specify a supplemental group
-, -l, --login make the shell a login shell
-c COMMAND pass a single command to the shell with -c
-f, --fast pass -f to the shell (for csh or tcsh)
-s SHELL run SHELL if /etc/shells allows it
-P, --pty create a new pseudo-terminal
-h, --help display help
-V, --version display version