newgrp

Switch to a different primary group

$ newgrp [group_name]

$ newgrp

newgrp [-] [group]

newgrp changes the current real group ID to the specified group. If a hyphen is provided, the environment is reinitialized as a login shell. Files created after running newgrp will have the new group as their group owner.
The user must be a member of the specified group or know the group password (if set). If no group is specified, the group is changed to the default group listed in /etc/passwd.

-

Reinitialize the environment as if the user had logged in

Group name to switch to; must be a member or know group password

This starts a new shell with the changed group. The original shell's group remains unchanged. Group passwords are rarely used and considered insecure. The change only affects the new shell and its children.

newgrp is a standard POSIX command that has been part of Unix systems since early versions. It provides a way to temporarily switch group context without logging out and back in.

groups(1), id(1), sg(1), gpasswd(1)