Bash script to replace text file from a lookup file

Shell Programming and Scripting
1

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

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

Mainfile.txt

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.

2

Please use code tags as required by forum rules!
Did you consider searching these forums 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,

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

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