Reading one line from a Unix domain socket

I have a server running socat with this command:

socat ABSTRACT-LISTEN:test123 PIPE

I can open a socket to this server, send one line, read one line, and print it with this code:

#!/usr/bin/perl

use strict;
use warnings;

use IO::Socket::UNIX;

my $sock = IO::Socket::UNIX->new(
    Type => SOCK_STREAM(),
    Peer => "\0test123"
) or die "Error creating socket: $!\n";

print $sock "Hello, world!\n";
my $line = <$sock>;
close $sock;

print $line;

When I replace the last 5 lines with the following, however, the program hangs:

print <$sock>;

Isn't the <FILEHANDLE> operator supposed to read one line from the handle? Why can I not read one line and print it?

Solution

print <$sock> is imposing list context to readline and thus reads and returns all lines until the end-of-file.

As noted in perlop :

If a is used in a context that is looking for a list, a list comprising all input lines is returned, one line per list element.

As noted by Hakon-Haegland in his comment below, a concise way to read only one line is to impose scalar context:

print scalar <$sock>