You'll need to select the filehandle that you wish to modify the buffering on before changing the $| variable that Ryszard points out.

An exception to that is STDOUT.
By default STDOUT is selected, so if that's the only filehandle that you want to turn buffering off for, then there's no need to select STDOUT first - just do $|++.

If you are changing the buffering on a number of filehandles, it's considered good practice to (re)select STDOUT before carrying out any other processing.
Not doing this might cause havoc with your print statements, and confuse anyone who has to maintain the code in future:

open(LOG, "> ./logfile") or die "$!";
open(DATA "> ./data")   or die "$!";
select LOG;
$|++;
select DATA;
$|++;
select STDOUT;
[download]

Another option is to use IO::Handle:

use IO::Handle;
open(LOG, "> ./logfile"); 
LOG->autoflush(1);
[download]

Have a look at perlfaq5 for more info and a slightly obfu way of using select :-)

Cheers.

BazB

Update: fixed code tag and small syntax changes.

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If the information in this post is inaccurate, or just plain wrong, don't just downvote - please post explaining what's wrong.
That way everyone learns.

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