//Adds new user group "dev" using Mac directory service command line utility
sudo dscl . -create /groups/dev


//Assigns some group id for the newly created group
sudo dscl . -append /groups/dev gid 2111


//Assigns password for the group
sudo dscl . -append /groups/dev passwd "xxxxx"


//Adds user with "username" to group "dev"
sudo dseditgroup -o edit -a username -t user dev


//List all the group available, and extract the newly created group 2111
sudo dscacheutil -q group | grep 2111


//To check whether the above entered information are proper, scroll the long list to find the dev group
sudo dscl . readall /groups



//Add the directory to dev group
sudo chown -R :dev /path/to/directory/



//Assigns read/write permission for owner and the members of the group
sudo chmod -R 770 /path/to/directory/