How to set a new password from bash?

Question

I'm using busybox with a limited passwd (I don't have --stdin option) and without chpasswd and I need to change the password of an user from bash. Here is my best result:

echo newpassword > pwdfile
echo newpassword > pwdfile
cat pwdfile | passwd myuser
Changing password for myuser
Enter the new password (minimum of 5, maximum of 8 characters)
Please use a combination of upper and lower case letters and numbers.
Enter new password:
Bad password: too simple.

Warning: weak password (continuing).
Re-enter new password:
passwd: The password for myuser is unchanged.

Answer 1

Busybox has chpasswd(8) which is a utility best used to create/update a lot of users very quickly and with one command. It accepts data from STDIN in username:password form. That means that you can do something like this:

$ cat pwdfile | chpasswd

or

$ < pwdfile chpasswd

Note that pwdfile must have username:new_password syntax.

Then again, you could always edit /etc/shadow yourself -- but please don't.