CODEWITHSUNDEEP
linuxshellubuntu
annieapple2000
annieapple2000

Reputation: 747

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.

Upvotes: 71

Views: 123599

Answers (9)

Jimmix
Jimmix

Reputation: 6556

If you want to ensure that an existing USER is added to the GROUP then this flow

if (group exists)
then
  (add user to group)
else
  (create group)
  (add user to group)
fi

can be simplified to:

if (group exists)
then
   # do nothing
else
  (create group)

fi
(add user to group)

then ... # do nothing can be removed and condition changed to if NOT exists to simplify the flow further

if (group NOT exists)
then
  (create group)
fi
(add user to group)

There is no need to check if (group NOT exists) if you may attempt to create a group and have no problem if it already exists. Thus the whole flow can be simplified to:

(create group) AND (add user to group)

how to do that in code

Upvotes: 0

Lemon Cat
Lemon Cat

Reputation: 1152

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

Upvotes: 29

Martin Bramwell
Martin Bramwell

Reputation: 2121

$ 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

Upvotes: 8

chiru
chiru

Reputation: 1007

Single line:

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

Upvotes: 10

JWL
JWL

Reputation: 14221

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.

Upvotes: 11

Alf Baez
Alf Baez

Reputation: 3

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

Upvotes: 0

kenorb
kenorb

Reputation: 166871

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

Upvotes: 4

Rupesh
Rupesh

Reputation: 1748

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

Upvotes: 27

andiba
andiba

Reputation: 1578

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

Upvotes: 111

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