Lua - find string in file the replace whole line

Hi,

I've been searching in Google for some Lua tips to try to update a text file using Lua, I need to replace an entire line when it contains or starts with a known string but the rest of the string on the line is unknown. I can do it in C# console app but thought it would be easier to do it directly in the my SUF installer.
-read text file
-find string and return line number
-replace line with new string.
Would doing this in Lua be possible or should I stick with the .net console app I made?

Thanks