Raspbian command usermod

Question

I have a question about usermod this command. I type as below:

sudo usermod -G adm -a pi
It is a normal way to append group "adm" to "pi" my raspberry. If I want to continue to append a lot of group such dialout, chrom, sudo, audio and others, how can I just type one script command only to make all groups to be? Currently, I append them each by each.

Wrong syntax: sudo user -G adm dialout chrom sudo -a pi

By the way, are there any books for dummies about this topics? I want to learn about shell-script, bash and more elaborate or essential commands about raspbian. Thanks

Answer 1

You can check the syntax for a command by reading the man page (Linux's built in help files):

man useradd

The relevant section is:

-G, --groups GROUP1[,GROUP2,...[,GROUPN]]] A list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma, with no intervening whitespace. The groups are subject to the same restrictions as the group given with the -g option. The default is for the user to belong only to the initial group.

You need to separate the groups with a comma and remove the whitespace, like this:

sudo usermod -G adm,dialout,chrom,sudo -a pi

As for a book, I started with Linux for Dummies way back in the mid 90's. The Raspberry Pi Foundation also publishes several ebooks, including Conquer the Command Line - which is free.

I can also recommend the Intro to Linux course from EdX