So you could do

#!/usr/bin/perl -w
use Expect;
my @mylog;
sub reporter {
#    print "PASSED:<",join("><",@_).">\n";
     push(@mylog,@_);
}

$object=Expect->spawn("some command I need");
$object->log_file(\&reporter);
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thank you very much. All the output can be store in the array but I still meet a small problem. I input ls command, and then print @mylog, but it doesn't contain the result of ls. When I input quit command to quit ftp, and then print @mylog, I get the ls result and quit result together. How can I solve this problem? Thanks a log. By the way, I use to meet this problem when I use C++ and C# to write the same program. In C++ and C#, anonymous pipe is used to implement it and I use multi-thread to solve the problem.

I still meet a small problem. I input ls command, and then print @mylog, but it doesn't contain the result of ls.

The reason for the difference, is because ls detects whether it's connected to a pipe or to a TTY, and behaves differently for both cases. You have to fool it into believing it's connected to a terminal. The common way to do that, is to connect it to a pseudo-terminal.

To this end, you can use the module IO::Pty. And judging by the documentation, Expect (which I've never ever used in my life, sorry) ought to have support for it built-in.

Happy hunting.

Well, from my experimenting with Expect it looks like the subroutine for logging the output is called when $object->expect is called, or even when $object->expect finds a match. Probably also when it's buffer becomes full, but you realy don't want to count on that.

My suggestion is to put in some $object->expect calls that match on whatever prompt you are getting in your input stream.

$exp->log_stdout(0);
my $output = $exp->before();
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if I send a command to a ftp process, and I want to store it's (sic) return value

Are you just doing FTP? Do you need to use Expect, or is there some reason why you can't/don't want to use Net::FTP? The code will be much simpler:

my $ftp = Net::FTP->new('foo.example.com')
  or die "can't connect: $@";

$ftp->login( 'leet', 'seKreT' )
  or die 'can't login: ' . $ftp->message;

$ftp->cwd("/pub/foo/bar")
  or die 'cannot set cwd' . $ftp->message;

my @files = $ftp->dir();
$ftp->quit;
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I just take ftp for example. However, thank you very much to tell me how to use Net::FTP :)