zssh (Zmodem SSH) is a program for interactively transferring files to a remote machine while using the secure shell (ssh). It is intended to be a convenient alternative to scp , allowing to transfer files without having to open another session and re-authenticate oneself.

http://zssh.sourceforge.net/

File transfer is achieved by using another tty/pty pair between the user and the local ssh process to plug either the user's tty (remote shell mode) or another process (file transfer mode) on the ssh connection.

ztelnet behaves similarly to zssh, except telnet is used instead of ssh. It is equivalent to 'zssh -s "telnet -8 -E"'

Files are transferred through the zmodem protocol, using the rz and sz commands.

zssh behaves as an usual ssh session until the escape sequence is depressed ( currently ^@ ), which enables file transfer mode. A new prompt is then displayed, and commands can be executed locally to initiate file transfers (among other things). It roughly behaves as a local shell featuring line edition, history and completion (thanks to libreadline), globbing, and escape characters ( " ' and \ ).

The following builtins are handled by zssh itself:

?  , cd , disconnect , escape , exit , help , hook , quit , repeat , rz ,
suspend , sz , version

— that's it, waited there indefinitely.