system ('ssh -O exit localhost 2> /dev/null;');
use Expect;
print Expect::version();
$su=new Expect;
$su->log_user(1);
$su->spawn ("ssh localhost echo aa");
$su->soft_close(); # this step hang 15 seconds
# $su->expect(undef);
exit 0;

##</code><code>##

system ('ssh -O exit localhost 2> /dev/null;
	ssh -M localhost -fN 2> /dev/null');
use Expect;
$su=new Expect;
$su->log_user(1);
$su->spawn ("ssh localhost echo aa");
$su->soft_close(); # this step now will not take more than 1 second
#$su->expect(undef);
exit 0;