command to add users to group

does a command exist to add users to more than one group?

i think the usermod command can do this but i'm not really sure. past ways of me doing this has always been to just hack the /etc/group file and put the user in whatever group i need him to be in. however, vi..ing files like /etc/groups or /etc/passwd is something i really dont like doing nor do i like anyone else doing. so, any ideas?

also, his there a command to list the users in a group?

to list the groups of the users the command is:

groups

and to add a user to a group the things to do are:

->get the current groups of the user by groups command
-> usermod -G grp1,grp2,newgrp username
-> logout and login again.

Note: if existing groups are not included in the usermod then those groups will be replace ny newgrp

cheers,

Guru