Using "use strict" command throws error "Bareword "SEEK_SET" not allowed ...

SEEK_SET is a constant imported from Fcntl (see seek, first paragraph):
    use Fcntl qw(SEEK_SET);
or
    use Fcntl qw(:seek);

Import it and restore use strict;

Update: So, WHENCE are you seeking if SEEK_SET is not defined in your program? My guess is it's the same as using 0, but that's not tested.