sg - execute command as different group ID
sg [-] [group [-c ] command]
The sg command works similar to newgrp but accepts a command. The command will be executed with the /bin/sh shell. With most shells you may run sg from, you need to enclose multi-word commands in quotes. Another difference between newgrp and sg is that some shells treat newgrp specially, replacing themselves with a new instance of a shell that newgrp creates. This doesn't happen with sg, so upon exit from a sg command you are returned to your previous group ID.
The following configuration variables in /etc/login.defs change the behavior of this tool: