Shell script: Determine whether users and user groups already exist/create users and user groups

Typically, as a deployment script for an application, the first task that begins is to create a dedicated (dedicated) user and user group for the current app. This script is very simple, a reference sample is attached here:

#!/bin/shuser=test_usergroup=test_group#create group if not existsegrep "^ $group"/etc/group >&/dev/nullif [$?- NE 0]then    groupadd $groupfi #create user if not existsegrep "^ $user"/etc/passwd >&/dev/nullif [$?-ne 0]the n    useradd-g $group $userfi

For adding users, we can also use the ID command to determine whether a user exists, so that the creation of a user's script can be written like this:

#create user if not existsid $user >&/dev/nullif [$-ne 0]then   useradd-g $group $userfi

However, using the ID command does not tell if a user group already exists! As for the use of id-g $user can only give an existing user to belong to the user group is what, and can not tell whether a user group is already exist, so, in order to use the script to handle the unified, we use unified from/etc/group and/etc/ passwd file to find out the way to determine whether a user group and users exist!

Shell script: Determine whether users and user groups already exist/create users and user groups