Hi

I type the password in bash shell. but it can be displayed what I typed

I take it that you found out that what you enter as a new password when running "passwd" is hidden. That is correct.

why?

Security. Even try to avoid that people look at your fingers when you set or enter passwords.

Thank you

If you are concerned to enter your password correct? That's why you have to retype it.

If you like to have different control over setting password checkout "man chpasswd".

Alexander