Check Whether a User Exists

Question

I want to create a script to check whether a user exists. I am using the logic below:

# getent passwd test > /dev/null 2&>1
# echo $?
0
# getent pa         


        

Answer 1

I like this nice one line solution

getent passwd username > /dev/null 2&>1 && echo yes || echo no

and in script:

#!/bin/bash

if [ "$1" != "" ]; then
        getent passwd $1 > /dev/null 2&>1 && (echo yes; exit 0) || (echo no; exit 2)
else
        echo "missing username"
        exit -1
fi

use:

[mrfish@yoda ~]$ ./u_exists.sh root
yes
[mrfish@yoda ~]$ echo $?
0

[mrfish@yoda ~]$ ./u_exists.sh
missing username
[mrfish@yoda ~]$ echo $?
255

[mrfish@yoda ~]$ ./u_exists.sh aaa
no
[mrfish@indegy ~]$ echo $?
2

Answer 2

You can also check user by id command.

id -u name gives you the id of that user. if the user doesn't exist, you got command return value ($?)1

And as other answers pointed out: if all you want is just to check if the user exists, use if with id directly, as if already checks for the exit code. There's no need to fiddle with strings, [, $? or $():

if id "$1" &>/dev/null; then
    echo 'user found'
else
    echo 'user not found'
fi

(no need to use -u as you're discarding the output anyway)

Also, if you turn this snippet into a function or script, I suggest you also set your exit code appropriately:

#!/bin/bash
user_exists(){ id "$1" &>/dev/null; } # silent, it just sets the exit code
if user_exists "$1"; code=$?; then  # use the function, save the code
    echo 'user found'
else
    echo 'user not found' >&2  # error messages should go to stderr
fi
exit $code  # set the exit code, ultimately the same set by `id`

Answer 3

Script to Check whether Linux user exists or not

Script To check whether the user exists or not

#! /bin/bash
USER_NAME=bakul
cat /etc/passwd | grep ${USER_NAME} >/dev/null 2>&1
if [ $? -eq 0 ] ; then
    echo "User Exists"
else
    echo "User Not Found"
fi

Answer 4

Create system user some_user if it doesn't exist

if [[ $(getent passwd some_user) = "" ]]; then
    sudo adduser --no-create-home --force-badname --disabled-login --disabled-password --system some_user
fi

Answer 5

Below is the script to check the OS distribution and create User if not exists and do nothing if user exists.

#!/bin/bash

# Detecting OS Ditribution
if [ -f /etc/os-release ]; then
    . /etc/os-release
    OS=$NAME
elif type lsb_release >/dev/null 2>&1; then
OS=$(lsb_release -si)
elif [ -f /etc/lsb-release ]; then
    . /etc/lsb-release
    OS=$DISTRIB_ID
else
    OS=$(uname -s)
fi

 echo "$OS"

 user=$(cat /etc/passwd | egrep -e ansible | awk -F ":" '{ print $1}')

 #Adding User based on The OS Distribution
 if [[ $OS = *"Red Hat"* ]] || [[ $OS = *"Amazon Linux"* ]] || [[ $OS = *"CentOS"*  
]] && [[ "$user" != "ansible" ]];then
 sudo useradd ansible

elif [ "$OS" =  Ubuntu ] && [ "$user" != "ansible" ]; then
sudo adduser --disabled-password --gecos "" ansible
else
  echo "$user is already exist on $OS"
 exit
fi

Answer 6

Late answer but finger also shows more information on user

  sudo apt-get finger 
  finger "$username"