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:

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1. #!/bin/sh
2. User=test_user
3. Group=test_group
5. #create group if not exists
6. Egrep "^ $group"/etc/group >&/dev/null
7. If [$?-ne 0]
8. Then
9. Groupadd $group
10. Fi
12. #create user if not exists
13. Egrep "^ $user"/etc/passwd >&/dev/null
14. If [$?-ne 0]
15. Then
16. Useradd-g $group $user
17. Fi

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:

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1. #create user if not exists
2. ID $user >&/dev/null
3. If [$?-ne 0]
4. Then
5. Useradd-g $group $user
6. Fi

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