Simulate user input in bash script

You should find the 'expect' command will do what you need it to do. It's widely available.

• See here for an example
• More examples here

A very rough example:

#!/usr/bin/expect
set pass "mysecret"

spawn /usr/bin/passwd

expect "password: "
send "$pass"
expect "password: "
send "$pass"

Here is a snippet I wrote; to ask for users' password and set it in /etc/passwd. You can manipulate it a little probably to get what you need:

echo -n " Please enter the password for the given user: "
read userPass
useradd $userAcct && echo -e "$userPass\n$userPass\n" | passwd $userAcct > /dev/null 2>&1 && echo " User account has been created." || echo " ERR -- User account creation failed!"