open my $oldin, '<&', \*STDIN or die $!;
open STDIN, '<&', \*DATA or die $!;

my $pid = system 1, 'perl -ne print';
print "pid: $pid\n";

close STDIN or die $!;
open STDIN, '<&', $oldin;

print "waiting for slave process\n";
waitpid $pid, 0 or die $!

__DATA__
hello world! (from DATA)