Shell script: Determine whether a user or user group already exists/create a user or user group

Shell script: Determine whether a user or user group already exists/create a user or user group

Generally, as a deployment script for an application, the first task is to create a dedicated user and user group for the current application. This script is very simple. Here is a reference sample:

#! /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] then useradd-g $ group $ userfi

For adding users, we can also use the id command to determine whether a user exists, so that a user's script can be written as follows:

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

However, you cannot use the id command to determine whether a user group already exists! To use id-g $ user, you can only give the user group to which an existing user belongs and cannot determine whether a user group exists, we use the/etc/group and/etc/passwd files to check whether a user group and user exists!