ssh2_exec() problem run simple command "ls"

[FD_F]

$con = ssh2_connect("127.0.0.1",22);
ssh2_auth_password($con, 'user', 'pass'); 
$stream = ssh2_exec($con, 'w');
stream_set_blocking($stream, true);
  $output = stream_get_contents($stream);
  echo $output;
  
  unset($con);

 

when i using ssh2_exec($con, 'w'); its ok

 

when i using simple linux  ls command -  ssh2_exec($con, 'ls'); i dont get any output

 

any idea why?, thanks

[FD_F]

solved i need wrote full path

/bin/ls