How to make a batch file add users to groups?

I need help with a GCSE project, I'm stuck on the last question. It asks for a bash script to create users, and then assign them to groups. I've already made the script add new users, but I'm unsure of how to add them to groups in the bash script (bash script made with nano).

Any help/examples?

My current script:

#!/bin/bash
# Script to add a user to Linux system
if [ $(id -u) -eq 0 ]; then read -p "Enter username : " username read -p "Enter password : " password egrep "^$username" /etc/passwd >/dev/null if [ $? -eq 0 ]; then echo "$username exists!" exit 1 else pass=$(perl -e 'print crypt($ARGV[0], "password")' $password) useradd -m -p $pass $username [ $? -eq 0 ] && echo "User has been added to system!" || echo "Failed to add a user!" fi
else echo "Only root may add a user to the system" exit 2
fi

(It looks something like that)

1 Answer

You can use this modified script:

#!/bin/bash
# Script to add a user to Linux system
if [ "$(id -u)" -eq 0 ]; then read -p "Enter username : " username read -p "Enter password : " password IFS=' ' read -a grps -p "Enter group names : " if grep "^${username}:" /etc/passwd &>/dev/null; then echo "$username exists!" exit 1 else pass=$(perl -e 'print crypt($ARGV[0], "password")' $password) if useradd -m -p "$pass" "$username" &>/dev/null; then echo "User has been added to system!" for grp in "${grps[@]}"; do usermod -a -G "$grp" "$username" && echo "User is added to group $grp" \ || echo "Failed to add user to group $grp" done else echo "Failed to add a user!" fi fi
else echo "Only root may add a user to the system" exit 2
fi

Note that you should always quote the variables.

Here i have added mainly two things:

• IFS=' ' read -a grps -p "Enter group names : " will ask root to give space separated group names to which the newly created user will be a member of

• Then this short for loop over the values of the array grps:

  for grp in "${grps[@]}"; do usermod -a -G "$grp" "$username" && echo "User is added to group $grp" \ || echo "Failed to add user to group $grp"
  done

Given the groups already exist. If not you can use groupadd to create the group and then add the user to that group.

Here we have used usermod to add the user to an existing group, these groups will be supplementary groups for the user.

Check man usermod for details.

Note that you should not use egrep, it is deprecated in favor of grep -E. In fact in this case you don't need grep -E.

Your grep pattern will fail in certain cases e.g. if you have a user foobar and you are adding a new user named foo. To overcome this, match the username followed by a : (given no username has :) :

grep "^${username}:" /etc/passwd &>/dev/null

Also send STDERR to /dev/null too.

This can be simplified as:

if grep "^${username}:" /etc/passwd &>/dev/null; then echo "$username exists!" exit 1
else ......

Also the next if statement with useradd can follow this.

**Also some other improvements can be made to your current script, that would not fit in this context.