#!/usr/bin/perl
use strict;
use warnings;

use IPC::Open3;

my $input;
my $pid = open3( $input, \*OUT, \*ERROR, "./foo.pl" );
my $rc = $?;
print "Rc=$rc\n";
...

#!/usr/bin/perl

print 1;

exit 3;

#!/usr/bin/perl

use strict;
use warnings;
use IPC::Open3;

my $input;
my $pid = open3( $input, \*OUT, \*ERROR, "./foo.pl" );
waitpid( $pid, 0 );
my $rc = $? >> 8;
print "Rc=$rc\n";

$ perl start_foo.pl
Name "main::OUT" used only once: possible typo at start_foo.pl line 9.
Name "main::ERROR" used only once: possible typo at start_foo.pl line 9.
Rc=3