You launch ssh without an absolute path name.

Have you made sure that $ENV{PATH} is the same when run via the web server as when run via the console?

Have you inspected the error message you get? $exp->error() might provide more information...

Thank you so much for your assistance! The subprocess that starts the ssh connection set the $ENV{"PATH"} = "/usr/bin"; (required by expect because of possible tainted return) The $exp->error() returns -1 after each interaction. Unfortuantly i'm very limited on the system i use, and i do not have access to Net::SSH::Any or IPC.

# assigns a job to a worker process.
# :param 0:     job.
# :return:
sub assign_job {
    my ($job) = @_;
    my $pid = open my $pipe => "-|";                    # create worke
+r process and connect it using a pipe.
    Debug::dlog("spawned process : $pid");
    die "Failed to fork: $!" unless defined $pid;       # check that c
+reation was successfull.
    my $routine = $job->get_routine();                  # get routine 
+to execute.
    my $params = $job->get_params();                    # get paramete
+rs to pass.
    unless ($pid) {                                     # the followin
+g code is only executed in the worker process:
        $ENV{"PATH"} = "/usr/bin";                      # delete conte
+xt.
        my $return = $routine->(@$params);              # execute rout
+ine.
        my $dump = Dumper($return);                     # serialize th
+e returned object.
        print($dump);                                   # print data s
+tring to pipe.
        Debug::dlog("process ".$$." dumped ".length($dump)." chars");
        exit;                                           # terminate pr
+ocess.
    } else {                                            # only in pare
+nt process:
        my $worker = new Worker($pipe, $pid);           # construct ne
+w worker object.
        push(@Dispatcher::workers, $worker);            # save worker 
+object.
    }
}
[download]

I think you can still remove Expect from the equation if you can manage a passwordless setup, by providing all the input to SSH via STDIN:

use File::Temp 'tempfile';
my ($fh, $output) = tempfile();
close($fh);

open my $remote, "| ssh $user\@$hostname >$tempfile"
    or die "Couldn't launch ssh ssh $user\@$hostname: $!";
print $remote "some test command\n";
print $remote "another test command\n";
print $remote "quit\n";

open my $fh, '<', $tempfile
    or die "Couldn't read the tempfile?!";
while(<$fh>) {
    print "Remote: $_";
};
[download]

But if you need to provide the password to SSH, there is no way to do that without Expect. All of this hinges on the idea of using (passwordless) ssh keys.