How to set or update Linux user password in a script

Problem statement:

Change or set a Linux user's password non-interactively. Consider a scenario that you have to create multiple user accounts with a default password on a server.

I can use passwd command, but it expects user input through stdin.

$ passwd foouser
Enter new UNIX password: [NEW PASSWORD]
Retype new UNIX password: [NEW PASSWORD]

So, it is certainly not handy when you have to create hundreds of user accounts and set their passwords, as one has to enter the same password twice per user multiplied by the number of user accounts to be created.

Solution:

We know that, passwd commands expects the new password to be provided through stdin twice, with a ENTER key i.e. new line separating those inputs. We can reproduce this using echo as:

$ echo -e "newpasswd\nnewpassword"
newpasswd
newpasswd

This way, we can send the password twice in one shot using echo command and a new line character \n as:

$ echo -e "newpasswd\nnewpassword" | passwd foouser

A better approach to set a user accounts password is to use chpasswd command. This command is used especially when you have to create multiple user accounts and set/update their passwords in a batch. It reads user-password pair from stdin in userName:newPassword format and changes the password of user account userName to newPassword.

With this, we can change the password of user account foouser to newpassword as:

$ echo "foouser:newpasswd" | chpasswd

Alternately, you can mention usernames and passwords in a file in userName:newPassword format, one pair per line, and feed that to chpasswd command.

$ cat secretfile
user1:newpassword1
user2:newpassword2
user3:newpassword3
...
...

$ cat secretfile | chapasswd

You can use any of this tricks in your script to automate changing or updating Linux user account's password. Try and let us know how it goes for you.