use Expect;

$Expect::Debug = 3;    # verbose debug output
$Expect::Log_Stdout = 1;  # show chatter for debugging
$Expect::Exp_Internal =1;
  my $exp = Expect->spawn("units")
    or die "Cannot spawn unit: $!\n";

$exp->log_stdout(1);
$exp->expect(15,
               [ qr/you have/i => sub { my $exp = shift;
               						print "you have";
                                     $exp->send("2 km");
                                     exp_continue; } ],
               [ qr/you want/i , sub { my $exp = shift;
               						print "you want"; 
               						$exp->send("m");
               						exp_continue; }],
               	[ 'eof', sub { my $exp = shift; print "eof"; print $exp->before(); } ],
               	[ qr/.*/, sub { my $exp = shift;
               					print $exp->error;
               					print $exp->before();
               		 } ]
              );

##</code><code>##

user@dell:~> units
2526 units, 72 prefixes, 56 nonlinear units

You have: 


##</code><code>##

spawn id(20): Does `'
match:
  pattern #1: -re `(?^i:you have)'? No.
  pattern #2: -re `(?^i:you want)'? No.
  pattern #3: -eof `'? No.
  pattern #4: -re `(?^:.*)'? YES!!
    Before match string: `'
    Match string: `'
    After match string: `'
    Matchlist: ()
Calling hook CODE(0x7fd8217449c0)...
Returning from expect successfully.
  spawn id(20): accumulator: `'
Closing spawn id(20).