Transfer perl output line by line to a file via unix command

I created a small perl programm in a unix enviroment:

#! /usr/bin/perl
use strict; 
use warnings; 

my $counter = 0;  
while ($counter < 10) {
  printf "%s\n", $counter;
  $counter++;  
  sleep(2);
}

If I start this at command line it will count from 0 to 9 in 20 seconds. That's what I want.

But if I use a command to transfer output to a file (myprog.pl >> myprog.log) then the output will be written at once at the end of the program (after 20 sec).

I want that the program writes it output line by line to the file. So after 10 seconds there s开发者_JS百科hould be 5 lines in myprog.log. Is there a way to do this?

That's expected buffering behavior, but your script can change that.

#! /usr/bin/perl
use strict; 
use warnings; 

$| = 1; # <------- Enable autoflush    

my $counter = 0;  
while ($counter < 10) {
  printf "%s\n", $counter;
  $counter++;  
  sleep(2);
}

An interesting discussion on the subject: http://perl.plover.com/FAQs/Buffering.html