Juerd already answered this from a Perl point of view. I'll answer the file oriented part of the question:
A file does have no notion of 'lines'. A file is an ordered collection of bytes with specific values. It is the software that reads and/or writes the file that decides what a line is.
The convention says that in the DOS/Windows world a line is delimited by CRLF and that in the UNIX world a line is delimited by LF. But this is only a convention. (Which is clearly indicted by the fact that DOS and UNIX have different conventions. ;-)
As long as your file system can cope with it, you can make the file as big as you want. You can thereby store as long a 'line' as you want in the file.