How to check if a group exists and add if it doesn't in Linux Shell Script

this is a summary of what i want my code to do:

if (group exists)
then

  (add user to group)

else

  (create group)

  (add user to group)

fi

I am using the Ubuntu virtual machine but all of the results i have found on similar sites do not work.

The grep statement in the solution of rups has some flaws:

E.g. grepping for a group admin may return true ("group exists") when there is a group lpadmin.

Either fix the grep-query

grep -q -E "^admin:" /etc/group

or use

if [ $(getent group admin) ]; then
  echo "group exists."
else
  echo "group does not exist."
fi

This script may help you:

   read -p "enter group name: " group
   if grep -q $group /etc/group
    then
         echo "group exists"
    else
         echo "group does not exist"
    fi

Grepping /etc/group works, but only on a machine where /etc/nsswitch.conf has:

group: files

meaning that only /etc/group is consulted when determining available groups. Use either of these (by name or by gid):

getent group <groupname>
getent group <groupid>

for a more generic solution, checking the exit status: 0 means "exists", non-zero means "does not exist". For example, to check to see if group 'postgres' exists, and create it if it does not (assuming bash shell, running as a user able to create new groups) run:

/usr/bin/getent group postgres 2>&1 > /dev/null || /usr/sbin/groupadd postgres

I've found it more useful, to compose andiba's solution into a proper function:

function grpexists {
    if [ $(getent group $1) ]; then
      echo "group $1 exists."
    else
      echo "group $1 does not exist."
    fi
}

This can for e.g be invoked into your environment by including this function in your /etc/bash.bashrc*, such that you can then check for the existence of a group, using the following spell:

grpexists group_name

Which should then return one of:

> group group_name exists.

or

> group group_name does not exist.

Single line:

$getent group <-groupname-> || groupadd <-groupname->

Here are 3 commands which should work:

group=sudo
grep -qw ^$group /etc/group || groupadd $group
usermod -aG $group $USER

Or one, when you use -f/--force (exit successfully if the group already exists):

groupadd -f mygroup && usermod -aG mygroup $USER

$ groupadd --help
Usage: groupadd [options] GROUP

Options:
  -f, --force                   exit successfully if the group already exists,
                                and cancel -g if the GID is already used

So you can do simply:

groupadd -f some_new_grp

Geeks great solutions and guidance, thanks for sharing here are my 2 cents to make our lives simpler or lazier :-) I could use to complement an useradd script I have to add several users at once. I'm wondering how it would look like inside a for in loop for several groups: group1, group2, group3...group6 Then useradd to the system something like this?

for g in $( cat fewgroups.txt ); do groupadd $g echo "Group:" $g "Exist not added moving on" else echo "Group:" $g "added successfully!" # Then create the users for u in $( cat 100sofusers.txt ); do useradd -m -g group1 -G group2,wheel -d /home/$u -c "Just anothe SiFiGeek" -s /bin/bash $u echo "userID:" $u "added successfully!" echo $u:$randompw | chpasswd echo "Password for userID:" $u "changed successfully" done