How to add users from data in a text file

Question

I have a question about creating multiple users in linux, but I need a program to work on it. There is a new users txt file, the content is following:

adams:5000:Adams, John Couch:/bin/bash
atiyah:5001:Atiyah, Michael:/bin/csh
babbage:5002:Babbage, Charles:/bin/csh
baker:5003:Baker, Alan:/bin/csh
barrow:5004:Barrow, Isaac:/bin/bash

... (there are 70 users name in the file)

I would like to know how to write a script to add those users automatically.

Solution 1

Lets say your file is named just file. This script will do the job:

USERNAME=$(cat file | cut -d: -f1)
echo "$USERNAME"

ID=$(cat file | cut -d: -f2)
echo "$ID"

USER_SHELL=$(cat file | cut -d, -f2 | cut -d: -f2)
echo "$USER_SHELL"

useradd -m -s "$USER_SHELL" -u "$ID" "$USERNAME"

Solution 2

This is a bare minimum script to get the job done. It makes sure that neither the username nor the uid is already in use. It makes a matching group for each user (with gid=uid) - it doesn't check if the gid or group name already exists (left as an exercise for the reader - hint: use getent group).

Note: the script below is untested but I've written scripts a lot like it a million times before (slight exaggeration)....there may be some minor bugs that need fixing.

#! /bin/bash
# get newusers file from first arg on cmd line or default to 'newusers.txt'
nf="${1:-newusers.txt}"

# get existing usernames and uids.
names="^($(getent passwd | cut -d: -f1 | paste -sd'|'))$"
 uids="^($(getent passwd | cut -d: -f3 | paste -sd'|'))$"

yesterday=$(date -d yesterday +%Y-%m-%d)
# temp file for passwords
tf=$(mktemp) ; chmod 600 "$tf"

while IFS=: read u uid gecos shell; do
    gid="$uid" ; homedir="/home/$u"
  
    useradd  -e "$yesterday" -m -d "$homedir" -c "$gecos" \
             -u "$uid" -g "$gid" -s "$shell" "$u"

    groupadd -g "$gid" "$u"
  
    # generate a random password for each user..
    p=$(makepasswd)
    echo "$u:$p" >> "$tf"
done < <(awk -F: '$1 !~ names && $2 !~ uids' names="$names" uids="$uids" "$nf")

# uncomment to warn about users not created:
#echo Users not created because the username or uid already existed: >&2
#awk -F: '$1 ~ names || $2 ~ uids' names="$names" uids="$uids" "$nf" >&2    

# uncomment the cat to display the passwords in the terminal
echo ; echo "passwords are saved in $tf"
# cat "$tf"

# set passwords using `chpasswd:
chpasswd < "$tf"

Use pwgen or makepassword or any similar program if makepasswd is not installed. Or write your own that concatenates 4+ random 5+ letter words to get an easy to remember password at least 20 characters long - capitalise some words and insert random 1-3 digit numbers and or a punctuation symbol between each word to make the password even longer and increase the brute-force search space. Random password generation is something that has been re-invented many times.

You can print out the usernames and passwords (from "$tf") and cut them into strips (leave a few blank lines between each user:password) to give to each user. Tell them to change their password immediately and destroy the strip of paper. The passwords are set to expire "$yesterday" (requires GNU date), so the users should be prompted to change them the first time they login to their shell.

Comments

[John]

What have you tried? We aren't going to write it for you, just help you figure out what is wrong with the script you are writing.

[Julie Pelletier]

Your input is really close to a password file entry, but you could use your distribution's built-in useradd (or similar) command with parameters extracted from the input.

[Alessio]

don't use backticks. use $() instead.

[Alessio]

it would probably be better to do this in perl...that's what i usually use for tasks like this.