temporary primary group

[MikeDougherty]

Is there a way to set my primary group temporarily (i.e. in just a single terminal session)? Sounds odd I know.

You see in order to use ClearCase I need to have "rational" as the primary group (why it doesn't work with me just being in the group I don't know...). But while doing most of my day-to-day work I prefer to have "users" as my primary group.

Thanks.