How do you change a user's primary group as they change directory

User1 is a member of Group1, Group2 and Group3, each group has a directory (say /home/group1, /home/group2, ...)

How do I make it so that when User1 cds to /home/group1, their primary group becomes group1, when they cd to group2 they become group2, etc?

Essentially, I'm only looking to do this so that when User1 makes a new file in each respective directory, it can be set group writable for the appropriate group.

I will be doing this on Solaris 10 (Although I am testing on Ubuntu 8.10...)

Thanks!

re: How do you change a user's primary group as they change directory

I suggest that u set up a cron that updates the permission once a file is created or check for any new file in the corresponding directory and update its permissions.

re: How do you change a user's primary group as they change directory

Another option would be to overload the cd command with a local script, so that if checks if the directory that it's changing to is in one of these places and if so change the default group.

Greetings,
Nepomuk