help need to "read from file until xxxx OR yyyy OR zzzz"

[Randy Padawer]

Hi, I would appreciate any help anyone may offer. Let's say a text 
file occasionally includes the words dogs, cats, and fleas. I need to 
"read until" any of these words without skipping any. I tried the 
following instruction, but of course that doesn't work:

open file FileName
     repeat
         read file FileName until "dogs" or "cats" or "fleas"
         -- (do something with it in found order)
     if it is empty then exit repeat
close file FileName

Unfortunately though, so far as I can tell, this script as-is 
(obviously so wrong) reads in the whole file and doesn't stop on any 
of the words.

I played with the "seek to"  command but that requires a number 
afterward... otherwise I would "seek to" all three of the keywords in 
question and then "read to" whichever came soonest and then repeat.

Can anybody point the way? Thanks again,

Randy