How to make a shell-like program which allows SSH password input?

Question

On OSX Terminal, I can connect to a server with SSH because terminal offers password input session.

$ ssh user@server.com
user@server.com's password: 

I wanted to make my own terminal implementation, so I

1. created pseudo terminal.
2. fork
3. redirected pty slave into stdin on child process.
4. exec bash.

And then, pushes string ssh user@server.com into pty master on parent process. But by program showed me this.

$ ssh user@server.com
Permission denied, please try again.
Permission denied, please try again.
Permission denied (publickey,password).

instead of password session.

What's my problem, and how can I fix it?

P.S. I know I can use expect utility. This is just a trial to implement my own pseudo shell application.

Update for later reference

The key to solution was using of forkpty() function instead of posix_openpt() function. Former one handles all hard annoying works, and gives me bi-directional master file number. I can read from and write to the file number. And the created pty device works perfectly. SSH login session works well. In contrast latter one still needs a lot of works which I never can figure out how.

I had to care about forkpty last two parameters. I thought them was output, but actually it was input. That was the source of all the problems, and after setting them to all NULL, it's working well now.

Answer 1

There is already a program which does what you want: sshpass

http://sshpass.sourceforge.net/

Since it is open source, you can examine its source to find out how it works.

Answer 2

I finally wrote pty device: https://github.com/eonil/PseudoTeletypewriter.Swift

My old Q/A describes some more: How to switch terminal to new child process of process launched with NSTask?