#!/usr/bin/perl

open my $ofh, '-|', '/usr/bin/perl', 'lazyread.pl' or die $!;

my ($inv, $ouv, $erv);
$inv = $ouv = $erv = '';
vec($inv, fileno(*STDIN), 1) = 1;
vec($ouv, fileno($fh), 1) = 1;
$erv = $inv | $ouv;

my $string = '';

{
    my $num = select
                 my $in = $inv,
                 my $out = $ouv,
                 my $err = $erv,
                 undef;
    sysread *STDIN, $string, -1, 10, length($string)
        or last if $in ne $inv;
    $string = substr($string, syswrite( $ofh, $string, length($string)))
        if $string && $out ne $ouv;
    redo;
}
__END__
#!/usr/bin/perl    # lazyread.pl

open my $fh, '>', 'lazy' or die $!;
while (<>) {
    print $fh $_;
    sleep 5;
}