How to use a while loop in BASH to iterate over all cPanel users on a server

Introduction

Making use of a BASH loop can greatly increase an administrator's efficiency when working with a large number of repetitive tasks.

Please keep in mind that the process of creating scripts, modifying scripts, and using a scripting language such as BASH is not related to cPanel or the basic configuration of cPanel, so cPanel support cannot provide assistance with this kind of system administrative task. If you need assistance with creating scripts you must reach out to a systems administrator with the skills, training, and experience required to assist you.

As a courtesy, we've created this basic guide to get you started in the right direction for using a while loop in a bash script.

Procedure

The following one-line script pipes all of the usernames on the server into a while loop that lists the email accounts for each user:

find /var/cpanel/users -type f | cut -d"/" -f5 | while read USERNAME;do echo;echo "Email Accounts for $USERNAME:";uapi --user=$USERNAME Email list_pops;done

One good way to break this down and understand it better is to execute each part of the script separated by the pipe ( | ) character.

For example, the first part of the script lists all of the files in the /var/cpanel/users directory:

find /var/cpanel/users -type f
/var/cpanel/users/cptest
/var/cpanel/users/cptest2

The next part of the script removes all but the username from the output of the previous part: 

find /var/cpanel/users -type f | cut -d"/" -f5
cptest
reseller

The next part of the script is the loop portion. When you pipe text into a while loop with the read command, the while loop will iterate over each part of the text separated by newlines. In our case each username is separated by newlines, so the loop will execute our code for each user. The username is stored in the variable that we set with the read command. Here is an example where we echo some text for each username:

find /var/cpanel/users -type f | cut -d"/" -f5 | while read USERNAME;do echo "This is the iteration for the $USERNAME user.";done
This is the iteration for the cptest user.
This is the iteration for the cptest2 user.

Once we get to this part, we can add just about whatever we want within the loop as long as we ensure that the syntax for the while loop is honored.  If you review the original example closely, you can see that the UAPI command to list email accounts is run for each user on the server.

Mastering BASH and the use of loops to accomplish administrative tasks will take time, practice, and research. If you would like to delve deeper into the topic of loops in bash, you can get started with the following guide:

Bash For Beginners - While Loop