use Capture::Tiny 'tee';
my $output = tee { system('t=1;while [ 1 -eq 1 ]; do echo hello $t; if [ $t -eq 10 ]; then exit 0; fi; t=$((t+1)); sleep 1; done') };
print $_ while( <$output> );

##</code><code>##

use strict;
use warnings;

# Script by bliako for https://perlmonks.org/?node_id=11100979
# spawns a system command and while running it sends its output
# to a client connecting via a socket.
# when the command terminates, the program waits for a client
# to send last pending output and exits too.
# 05/06/2019

use IO::Socket::INET;
use IO::Select;
use Scalar::Util qw/openhandle/;
use POSIX ":sys_wait_h";

my $EXEC = undef;
my $keep_on = 1;
$SIG{CHLD} = sub {
	waitpid(-1,WNOHANG);
	$keep_on = 0;
};

my $port = 20000;
my $cmd = 't=1;while [ 1 -eq 1 ]; do echo hello $t; if [ $t -eq 10 ]; then exit 0; fi; t=$((t+1)); sleep 1; done';
my $execpid = open($EXEC, '-|', $cmd) or die "failed to spawn command $cmd : $!";
die "spawning system command, $!" unless defined $execpid;
print "PID is $execpid\n";

# Listen to port
my $sock =
 IO::Socket::INET->new(LocalPort => 20000,
                       Type      => SOCK_STREAM,
                       Proto     => 'tcp',
                       Listen    => SOMAXCONN,
                       Reuse     => 1,
		       Timeout   => 1,
                       Blocking  => 0
 ) or die "Can't create socket, $@";


my @cmdoutput;
my $aselect = IO::Select->new();
$aselect->add($sock);
$aselect->add($EXEC);
#local $/ = undef;
WHITER: while(){
	my @clients = $aselect->can_read(1);
	foreach my $aclient (@clients){
		if( $aclient == $EXEC && $keep_on){
			print "$0 : select the EXEC ...\n";
			if( openhandle($EXEC) ){
				# checking 
				print "spawn command lives\n";
				push @cmdoutput, <$EXEC>;
			} else {
				print "spawn command ended\n";
				push @cmdoutput, '<close>'; $keep_on = 0;
			}
		} elsif( $aclient == $sock ){
			print "$0 : select a client via socket ...\n";
			if( ! $aclient->connected() ){ $aselect->remove($aclient) }
			$aclient = $sock->accept();
			$aselect->add($aclient);
			# send them a message, close connection
			$aclient->print(join("",@cmdoutput));
			print "$0 : got a request and send the cmd output so far.\n";
			@cmdoutput = ();
			if( ! $keep_on ){
				# command has ended but wait for a client to send all pending output
				$aclient->print("<closed>\n");
				print "$0 : terminating after send client pending output.\n";
                                $aclient->close();
                                $aselect->remove($aclient);
				last WHITER
			}
			$aclient->close();
			$aselect->remove($aclient);
		}
	}
}
print "$0 : done.\n";

##</code><code>##

# example use:
perl a.pl &
telnet localhost 20000