In do_log you are calling a subroutine called move, what does that do? Did you mean rename perhaps? It's an easy mistake to make - the UNIX program mv(1) calls the kernel API rename(2), which is also called by Perl (on Windows the command-line program is called rename but the API is called MoveFile!). However, I would have thought that you would have at least got a warning for that.

In check_nr_of_line you are using $fh, which is a bit suspicious since you close $fh in do_log. Check the return code from the seek?