How to use a while loop in BASH to iterate over all items in a file

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. 

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 email accounts in the emailaccts.txt file to a while loop. The while loop will execute the UAPI call to provide the Email Client Settings for each email account.

cat emailaccts.txt | while read EMAIL;do uapi --user=cpanelusernamehere Email get_client_settings account=$EMAIL;done

A good way to better understand what is happening in the script is to break it into each part separated by the pipe ( | ) character.

For example, the first part prints the contents of the emailaccts.txt file:

# cat emailaccts.txt
email1@cptest.tld
email2@cptest.tld

Notice that the contents of the file are email accounts separated by newline characters.

The second part is the while loop. The while loop uses the read command to set the $EMAIL variable for each email address. 

For each email address, the while loop executes the UAPI call and expands the $EMAIL variable so that you get the output specific to that email account.

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