execute set of commands with dbclient

[Antony Pavlenko]

Hello,
I'd like to use dropbear clieant for remote execution of 
set of
commands. Anf read this commands from external file.
But now i confused with sending commands. As i understand 
it's ok to do
it in send_chansess_shell_req function (as it is done for 
"command").
But i couldn't understand how to write command.
Now i'm trying so :

start_channel_request(channel, "exec");
buf_putstring(ses.writepayload, buffer, strlen(buffer));
encrypt_packet();

where buffer is char array with command, but it isn't 
work.
What's wrong?
Can anybody help me?

with respect,
---
Antony Pavlenko