my @letters = ( 0 .. 9, 'a' .. 'z' );

open FILE, '>', 'list' or die "Cannot open 'list' because: $!";

for my $i0 ( @letters ) {
  for my $i1 ( @letters ) {
    for my $i2 ( @letters ) {
      for my $i3 ( @letters ) {
        for my $i4 ( @letters ) {
          for my $i5 ( @letters ) {
            for my $i6 ( @letters ) {
              for my $i7 ( @letters ) {
                print FILE "$i0$i1$i2$i3$i4$i5$i6$i7\n";
              }
            }
          }
        }
      }
    }
  }
}
close FILE;