my $guest_file = "../new_guestbook.html"
#                                       ^
# Insert semicolon here ----------------/

##</code><code>##

seek GUEST, 0,0; # Filehandle should be GUESTS

##</code><code>##

foreach my $guest (@guest) { # Should have been @guests

##</code><code>##

open (GUESTS, "+>> $guest_file") or
    or die "Can't open $guest_file: $!";