Shell Programming and Scripting

Hello
I need to search for a mult-line strngs(with spaces in between and qoted) in a file1 and replace that text with Fixed string globally in file1. The strng to search for is in file2.

The file is big with some 20K records. so speed and effciency is required

file1: (where srch & rplc will happen) e;g lets say 5 lines in file are;

Thebare book_names='Unix1 Best' and then editor_ranks='Honsun' where live.
Science is another Line_no1='Number Whole' and look for ppl and data
Lets have person='Noro' and past Noro and Unix1
This is nothing to do
Next line is Honsun

file2string to be srched)
book_names
editor_ranks
Line_no1
person

I need to replce all these strgs value with XXX. Also need to replace all occurances of these values globaly in file.

Expetd file:
Thebare book_names=XXX and then editor_ranks=XXX where live.
Science is another Line_no1=XXX and look for ppl and data
Lets have person=XXX and past XXX and XXX
This is nothing to do
Next line is XXX

Any ideas? Need urgnt help