I don't think that there is any variable or core module that you can query to get this information. You could check
$^O (see
perlvar) or
Config to get the OS name and work it out from there. However, it might not be easy to produce a foolproof solution with this method.
As a workaround I'd suggest writing "\n" to a temp file, binmoding the file and reading back in the character(s) used as line endings.
--
John.