....
open RNDNUM, '<randoms' or die $!;
binmode(RNDNUMS); # If needed!
seek RNDNUMS, -4, 2;
my $newlen = tell RNDNUM;
my $rndnum = do {
     local $/=\4; 
     unpack 'I',<RNDNUM>;
}
truncate RNDNUM, $newlen or die $!;
close RNDNUM or warn $!;
.....
# do whatever with $rndnum