@array = <FILE>;
$last_line = $array[$#array];

##</code><code>##

seek(FILE, -81, 2);             # 81 bytes from the end, which should be enough
@lines = <FILE>;
$last_line = $lines[$#lines];   # similar to above, but we don't read much

##</code><code>##

tie *FILE, File::ReadBackwards 'input_file';
while (<FILE>) {
   # line-by-line starting from the end
}