I've gotten a bit closer, but not quite there yet

#!/usr/bin/perl

use strict;
use Net::SSH2;

my $ssh = Net::SSH2->new();

$ssh->connect('10.10.10.10') or die;

if ($ssh->auth_password('zzz','xxx')) {
  $ssh->debug(1);
  my $chan = $ssh->channel();
  $chan->shell();
  print $chan "microcom /tmp/dev/mux1\n";
  sleep(10);
  print $chan "AT+CSQ";
  select(undef,undef,undef,3.0);
  my ($len, $buf);
  print $buf while ($len = $chan->read($buf,1)) > 0;
  $chan->close;
} else {
  warn "auth failed.\n";
}
[download]

This one clearly shows me that the AT+CSQ is not passed on - when connecting to the modem, it will report "ERROR" after ~20 seconds of nothing going on. And it does just that. Any ideas on how to move on from here?