How to pass password to su

su command only accept password from terminal in normal case. The following is using "expect" command to overcome this restriction. However this is not secure.

You must install expect package before using this command.

http://blog.roodo.com/ystuan/archives/6128305.html
https://blog.longwin.com.tw/2011/07/expect-shell-auto-linux-2011/

We can use autoexpect tool to help us to build the script.

#!/usr/bin/expect -f
set timeout -1
spawn su -c {cp /tmp/a.txt /tmp/b.txt}
match_max 100000
expect -exact "Password: "
send -- "your_root_password\r"
expect eof


However this is not secure, it will leave your root_password in this file.
We should use sudo -S to do this job.

http://blog.roodo.com/ystuan/archives/6128305.html
https://blog.longwin.com.tw/2011/07/expect-shell-auto-linux-2011/