This code...

#!/usr/bin/perl

use strict;
use warnings;

use IO::Pipe;
use IO::Handle;
use IO::Select;

my $pipe = IO::Pipe->new();

my $pid = fork();
die "failed to fork: $!" unless defined $pid;

if ($pid) {
    $pipe->reader();

    my $select = IO::Select->new();
    $select->add($pipe);

    while (1) {
        my @ready = $select->can_read(1);

        foreach my $h (@ready) {
            my $line = <$h>;
            chomp $line;
            print "PARENT sees <$line>\n";
        }
    }
}
else {
    $pipe->writer();
    $pipe->autoflush(1);

    my $c = 0;
    while (1) {
        $c++;
        print "CHILD writing <$c>\n";
        $pipe->print("$c\n");
        sleep 1 unless $c % 5; # pause after each fifth line
    }
}

[download]

produces output like this...

CHILD writing <1>
CHILD writing <2>
CHILD writing <3>
CHILD writing <4>
CHILD writing <5>
PARENT sees <1>
CHILD writing <6>
CHILD writing <7>
CHILD writing <8>
CHILD writing <9>
CHILD writing <10>
PARENT sees <2>
PARENT sees <3>
PARENT sees <4>
PARENT sees <5>
PARENT sees <6>
CHILD writing <11>
CHILD writing <12>
CHILD writing <13>
CHILD writing <14>
CHILD writing <15>
PARENT sees <7>
PARENT sees <8>
PARENT sees <9>
PARENT sees <10>
PARENT sees <11>

[download]

And so on.

What do I need to do to avoid the buffering of child writes that seems to be occuring?

This is on Debian/Linux.

In reply to buffering when reading from unnamed pipe with child process by Santasha

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