How to share .bash_profile between different users in the same group?
i work it out by using command ln -s /Users/user2/.bash_profile /Users/user1/.bash_profile. 
But by only this command, i can only change the .bash_profile in user2. in user1, you can only use the file in the read-only mode. Then i check the .bash_profile privilege in user2. its rw-r--r--. So i do chmod 664 /Users/user2/.bash_profile. Finally i can share the .bash_profile in different users.