How can I automate adding a new user, using an existing user's groups?

Question

Raspberry pi comes with a default user account that is added to multiple groups:

username@hostname:~ $ groups pi
pi : pi adm dialout cdrom sudo audio video plugdev games users input netdev spi i2c gpio

I'd like to script adding a new primary user with the same group membership as the default. I think this would also be practical for adding new admins to any Unix/Linux system. Windows has the functionality from ADUC by Copying an existing account.

I believe the script will need to:

1. Use a loop
2. Prompt for existing username (eu) input
3. Store the existing user's current groups as a variable (eg) - groups
4. Prompt for new username (nu) input
5. Add the new user with the existing user's groups - useradd

I presume this will work to also gain sudo permission, based on ændrük's answer to a similar question. Another similar question is Rahul's about adding a list of users to multiple groups.

Answer 1

Given a template user of some sort, like your default pi user on Raspbian, etc.

First, create a new user -

adduser newuser

Then put them in all the same groups as the pi user

for i in `grep -E "(:|,)pi(:,|$)" /etc/group|cut -f1 -d:`
do
  adduser newuser $i
done

Be very careful about giving too much access. Also, remember that a user has to log completely out and then log back in before group membership really changes.