From manpage of sudo:
Write the prompt to the standard error and read the password from the standard input instead of using the terminal device. The password must be followed by a newline character.
What is the purpose of using
sudo -S instead of just
Is it correct that
sudoby default read password from standard input?
What is the purpose of "Write the prompt to the standard error"? Does
sudoby default write it to the standard output?
Do they both require that the password must be followed by a newline character?
For example, in https://stackoverflow.com/a/39553081/156458,
sudo -S true still requires typing in password, so how does it solve the original question in that post? I found that link when I searched for solution to Shall I run a sudo-required script in some shell configuration file?
The reply by J.Taylor said
sudodoes not read the password from stdin by default - it reads it from the terminal interface.
I was wondering how to understand it in terms of implementation.
Is it correct that when a program reads from standard input, it reads from file descriptor 0 to which the standard input is always binded?
Why can't I tell whether
sudo uses standard input or terminal when using
How can a program (such as
sudo -S) achieve to read from terminal instead of standard input?