#!/usr/bin/perl
print "Content-type: text/html\n\n";
srand();
$fil="ch";
open(OUT, '>>'.$fil);
for($i=1;$i<10001;$i++){
 $j=int(rand(20000))+440000;
 $k=substr(pack('l>',$j),1);
 print OUT $k;
}
close(OUT);
print "DONE !";
[download]

Add binmode OUT after the open.

Also,

1. you should be using a mode of '>' not '>>', unless your intention is to append to an existing file.
2. for($i=1;$i<10001;$i++){ is more easily and clearly written as for my $i ( 1 .. 10000 ) {
3. int(rand(20000))+440000 produces always positive integer.

   If you don't need signed integers, your question would have been much simpler to answer.

4. $k=substr(pack('l>',$j),1); print OUT $k;

   Packing and writing one value at a time is hugely expensive compared to packing all 10000 values in a single pass and then writing them once.

5. For goodness sake, use a little horizontal whitespace.

   Don't you find this infinitely more readable?

   #!/usr/bin/perl
   use strict;
   
   print "Content-type: text/html\n\n";
   
   srand();
   
   my $fil = "ch";
   open( OUT, '>', $fil ) or die $!;
   binmode OUT;
   
   for my $i ( 1  .. 10_000 ) {
       my $j = int( rand( 20_000 ) ) + 440_000;
       my $k = substr( pack( 'l>', $j ), 1 );
       print OUT $k;
   }
   
   close( OUT );
   print "DONE !";
   [download]

   Remember that your source code is the equivalent of the professional chef's plated up meal.

   His presentation is what makes the difference between a paid for cover and a decent home cooked meal. It is both his edge and his profit margin.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Hi BrowserUk, Many thanks for your pertinent remarks and sorry for my bad code formatting, especially from a guy whose his father was a French cooking chief :-) In fact I append many integer values thus the ">>". And they could be negative, because they are latitudes and longitudes worldwide. I was also using the old fashioned format in the "for" loop... But despite using the "binmode" instruction, the resulting file is longer than 30000 chars for 10000 iterations, typically 30035 !!! Please, do you have any idea for this strange behaviour ?

I actually downloaded the >>8 version before it changed.

Apparently. Sorry.