You must specify the process to send input to, and the input data to send.
Some operating systems have limited space for buffered input in a pty .
On these systems, Emacs sends an eof periodically amidst the other characters, to force them through. For most programs, these eof s do no harm. The argument process-name must be a process or the name of a process. If it is nil , the current buffer's process is used. The function returns nil .