Hi all,

I'm trying to write a program which forks off a child process. The child needs to send message to the parent, where a message is just a string followed by a newline. The problem I am experiencing is that the parent only reads one message although multiple messages were sent. Here is a short test script:

use strict;
use warnings;

use IO::Select;
use IO::Socket;

my $child = my $parent = my $pid = undef;

# Create a socket pair for IPC (both ways)
socketpair($child, $parent, AF_UNIX, SOCK_STREAM, PF_UNSPEC);

$child->autoflush(1);
$parent->autoflush(1);

if (!defined($pid = fork())) {
    die $!;
}
elsif ($pid == 0) {
    close($child);

    print $parent "LINE1\nLINE2\n";

    sleep(5);
    close($parent);
    exit 0;
}
else {
    close($parent);

    # Make sure the client has already started and sent the two lines
    sleep(2);

    my $ios = IO::Select->new($child);
    while (my @handles = $ios->can_read(0)) {
        foreach my $handle (@handles) {
            my $message = <$handle>;
            print "Read message: ".$message;
        }
    }
    close($child);
}
[download]

My questions:

Why does IO::Select not return the handle when there is still data to read after the first line?

How can I read all messages, without ever blocking the parent?

Thanks for your help

---

In reply to Reading from a pipe line by line by Marcello

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