Shell Programming and Scripting

Hi,
This is most likely a dumb question but I could not find answer to it elsewhere.

I'm building a simple menu with case /esac and want to read user's input:

Please enter XYZ ; read XYZ

How do I take the value of XYZ and insert it as a variable $XYZ in file file.txt ?

I may need to explain that I have existing variable IP="address" in file.txt and I need to substitute address with XYZ from the user's input

What else is in file.txt?

A long script

I have
IP="address" as a variable on the 4-th line

The point is to be able to take user's input for IP address and insert it into this file so it is a valid IP to be used throughout the script

Why insert it? Why not just use it? This is a strange-sounding system.

You could export it, and set it only in that script if it's not already set.

Code:

# outside the script
read IPADDRESS
export IPADDRESS
./myscript

Code:

#inside myscript, set the variable if nothing else did
[ -z "$IPADDRESS" ] && IPADDRESS="default.ip.address"

That way you don't need to hack apart your scripts with sed all the time, which sounds a recipe for disaster if I ever heard one...

You may be right. But how do I do that?

My Main Menu script is in one file that I execute first to define the values which are then inserted and the variable in the other file

What is the alternative?

I may have stealth-edited underneath you, see my example.

Code:

${IPADDRESS:=ZZZ.XXX.YYY.AAA}

Will set the value of IPADDRESS to ZZZ.XXX.YYY.AAA if the variable had no value...