I have two applications where I want the main application to receive the output from STDERR/STDOUT in real time (i.e. when data is printed) from the other application. However, it seems like the main application is waiting or is blocked so it cannot print simultaneously. Any suggestions?

The executed application

#!/usr/bin/perl
use Process;
$| = 1;
print STDERR "Started ..!\n";
Process::createProcess('./printApplication');
print STDERR ".. Finished!\n";
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The print application

#!/usr/bin/perl
print STDERR " printing some text\n";
print STDERR " printing some text\n";
print STDERR " printing some text\n";
print STDERR " printing some text\n";
sleep 10;
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The library that contains execute functionality

package Process;
use strict;
use warnings;
use IO::Select;
use IPC::Open3;

sub createProcess ($) {
    my($path) = @_;
    my($selector, $pid, @ready, $fh, $line);

    $pid = open3(*CMD_IN, *CMD_OUT, *CMD_ERR, $path);
    $selector = IO::Select->new();
    $selector->add(*CMD_ERR, *CMD_OUT);

    while(@ready = $selector->can_read()) {
        foreach $fh (@ready) {
             if(fileno($fh) == fileno(CMD_ERR)) {
                 $line = scalar <CMD_ERR>;
                 if(defined $line) {
                    print STDERR $line;
                 }
              }
              else {
                 $line = scalar <CMD_OUT>;
                 if(defined $line) {
                    print STDOUT $line;
                 }
              }
             $selector->remove($fh) if eof($fh);
          }
      }
    waitpid($pid, 0);
}
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UPDATE: I want the main application to print out the output from the second application immediately.
Currently, it waits for the sleep function to finish, THEN prints.