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

[Randy Padawer]

Thanks for the comments. Well, the problem with reading the whole 
file at once is that some of these files can indeed be huge -- 
several megabytes. Here's what I'm doing... The text file is made up 
of many individual emails concatenated end-to-end. Since the emails 
may have originated from different ISP accounts, they may use 
different delimeters, i.e., ">From " or "X-Message-Info: " or 
"Return-Path: <" or "From ???@???". I have written a simple program 
that will separate the huge file back into individual text files, one 
for each email. It works well if the email is from a single account 
(with its unique delimeter). However if, say, Apple's mail.app is 
pulling mail from multiple accounts, I can't "read from" any of those 
delimeters. Can I do the regex routine (something I don't quite yet 
understand... but will soon!) on a file I've not wholly read? Thanks 
again for your great help. -- Randy