Find string and replace line in linux

Question

I'd like to do the following, but I can't seem to find an elegant way to do it.

I have a text file that looks like this:

..more values
stuff = 23   
volume = -15
autostart = 12
more values..

Now the "volume" value may change, depending on the circumstance. I need a script that can find that line of text with "volume = xxx" then replace it with the line "volume = 0". What is an elegant solution to this? This line in the text is not guaranteed to be the first line, so I need a way to find it first.

Answer 1

sed 's/^volume =.*/volume = 0/g' file.txt

Answer 2

With sed you can say:

sed '/^volume/s/.*/volume = 0/' infile