adding text to the end of lines containing a word

I'm new to shell scripting, and need to add a series of commands to the ends of certain lines of text that contain a keyword. Any easy way to do this? Thanks

There are several ways to accomplish most any task with unix. It is best possible to answer when seeing sample input data and desired output data.

try sed:

sed 's/[A-Z a-z0-9].*keyword[A-Za-z 0-9].*/& extra commands go here/' filename > newfile