Multi-line Find and Replace

I want to be able to open up a text file, find a string, and replace it with something else. The thing is, the thing that I'm finding is multiple lines. So basically...I want to find this:

line1
line2
line3

and replace it with this

blah1
blah2
blah3

I know about this - http://nsis.sourceforge.net/archive/....php?pageid=17 - but I can't figure out how to get that to work for multi line stuff. Can anyone help me out?

this should work fine

It reads one line at a time, so I doubt that will work. You should not read one line but a certain number of bytes.