Well, 420KB is not really such a large file. Perl should have no trouble at all holding that much data in memory (unless you are working on a really old, dinky little machine). As for the code you posted in your update:

• When I looked at it, it seemed not to be reading any input at all -- you had this line commented out:

  #@Data = <F>;
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  and nothing else in the code was reading from the input file.

• You seem to be reading tagged data of some sort (HTML? XML?), so you should be using an appropriate parsing module (HTML::TokeParser, XML::Parser, or some variant/derivative of one of those).

• The reason for using a parsing module is to avoid the sorts of mistakes that you are probably making:

  $_=~ s/(<[^<>]+>)+//g; chomp;
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  Since you are processing the data line by line, if any tags contain a newline between the angle brackets, they will not be deleted by that regex.

• Some of your logic seems to make no sense; after attempting to delete everything that looks like a tag, you check for the presence of an open-paren, and then you perform the same two steps in both the "if" and the "else" blocks.

It would also help to show a little bit of input data -- or at least the part that you say gets "cut off", and give a little more detail about what is meant, exactly, by "It gets cut off". What / how much is missing from the output?