Shell Programming and Scripting

Hi. I need assistance with the replacing of text into a specific file via a bash script.

My bash script, once run, currently provides a menu of computer names to choose.The script copies onto my system various files, depending what computer was selected in the menu.This is working OK.

Now, I need to update certain other files depending on what computer was selected.I have created an example scenario below.
I have a file called mainfile.txt and a lookup file called lookupfile.txt.
If I run my script and chose the option for Computer A, a variable is set in my script, e.g. $ComputerA

What I now need is for the ‘DomainName=’ in my mainfile.txt to update with the full domain name of ComputerA that’s detailed in the lookupfile.txt

Lookupfile.txt

Code:

ComputerAcomputerA.testdomain.com192.168.1.1
ComputerBcomputerB.testdomain.com192.168.2.1
ComputerCcomputerC.testdomain.com192.168.3.1

Mainfile.txt

Code:

DomainName=

From researching the issue I believe I can use awk or sed.However, I have had difficulty finding examples like I to get it working.
Can anyone provide a solution (and possibly an explanation of the solution).I can re-format my lookup.txt file if required Many thanks.

Please use code tags as required by forum rules!
Did you consider searching these fora for examples?

Your lookup file doesn't have any field separators, so a translation might run into trouble.
Given your table had <TAB> field separators,

Code:

grep $C file | cut -f2
computerA.testdomain.com

could do what you want. Use command substitution to assign to a variable.