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

Typically, as a deployment script for an application, the first task that starts is to create a dedicated (dedicated) user and user group for the current app. This script is very easy. Here is a sample of references:

#!/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 the user to join, we can also use the ID command to infer whether a user exists, so that the creation of a user's script can write:

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

But. Using the ID command does not infer if a user group already exists! As for the use of the id-g $user can only give an existing user group to which they belong, and cannot infer whether a user group already exists. Therefore, in order to use the script to handle the unified. We use the same method of finding from/etc/group and/etc/passwd files to infer whether a user group or user exists!

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