open(DATA, "$db") || die "Can not open: $!\n";
my @dat = (<DATA>);
close(DATA);
open(DATA, "$db") || die "NO GO: $!\n";

##</code><code>##

while (<DATA>) {
   # ...
   open(DATA,"> test4.txt") or die $!;;
   # ...
}

##</code><code>##

my $i = 0;
while ($i < 5) {
   open (OUT, '>oops.txt') || die "NO GO: $!\n";
   print OUT $i;
   $i++;
}

##</code><code>##

open (OUT, '>oops.txt') || die "NO GO: $!\n";
my $i = 0;
while ($i < 5) {
   print OUT $i;
   $i++;
}