Not sure if you have been answered in the Chatterbox already, so...

So the the BEGIN { $/ = "}\n" } changes the input record separator?

Yes. See $/ in perlvar.

Should I substitute REGEX with the regex for the find, and the STRING with the replace? Not sure how much of this actually goes in the shell prompt. Did you write REGEX and STRING as placeholders? Can anyone assist?

I, also, cannot test jwkrahn's code of Re: find and replace from shell, but it looks like it should work as it stands. The  <<REGEX and  <<STRING begin 'here-documents': see <<EOF in perlop. What happens when you try the code on an expendable test file?