问为什么使用ssh2_exec的命令不结束？

EN

$stream =ssh2_exec($connection, 'cd /home; wget http://domain.com/myfile.zip; unzip myfile.zip; rm myfile.zip');

<?php 
$ip = 'ip_address'; 
$user = 'username'; 
$pass = 'password'; 

$connection = ssh2_connect($ip); 
ssh2_auth_password($connection,$user,$pass); 
$shell = ssh2_shell($connection,"bash"); 

//Trick is in the start and end echos which can be executed in both *nix and windows systems. 
//Do add 'cmd /C' to the start of $cmd if on a windows system. 
$cmd = "echo '[start]';your commands here;echo '[end]'"; 
$output = user_exec($shell,$cmd); 

fclose($shell); 

function user_exec($shell,$cmd) { 
  fwrite($shell,$cmd . "\n"); 
  $output = ""; 
  $start = false; 
  $start_time = time(); 
  $max_time = 2; //time in seconds 
  while(((time()-$start_time) < $max_time)) { 
    $line = fgets($shell); 
    if(!strstr($line,$cmd)) { 
      if(preg_match('/\[start\]/',$line)) { 
        $start = true; 
      }elseif(preg_match('/\[end\]/',$line)) { 
        return $output; 
      }elseif($start){ 
        $output[] = $line; 
      } 
    } 
  } 
} 

?>