UNIX for Dummies Questions & Answers

Hi,

I am confused between using here document and using expect for writing interactive shell scripts(like changing password ,FTP or doing su).
My questions are :
1)Why here documents cant change password from shell script.
2)Why we need to use expect for same?
3) Can Sourcing a script can do FTP or change password? like

Code:

. myscript.ksh

or

Code:

source myscript.ksh

4) What is the difference in all three behaviors(here,expect and source)?

Tried to resolve these on own but still i am confused.

Thanks

In order to change a password or run sftp with an 'interactive' password requires that the process breaks off from the parent and becomes a session leader. The session has no attached tty.

This is what a daemon process and expect do.

passwd and sftp and ssh are designed to prevent security breaches. Putting a password in plaintext in a script is a security breach

Go here:
http://www.rite-group.com/rich/ssp/index.html

download the source code, find the pty.c program under the pseudo_term directory -- this is what expcect does so that people can get around the inbuilt security of passwd for example.

Thanks jim .
But for sourcing no sub shell is created and it runs in parent shell.
So why script run as sopurce cant be used to change shell?

Is it that when i issue passwd command on machine, a new process is created to assist it ?