Question

I’m writing a shell script to automatically add a new user and update their password. I don’t know how to get passwd to read from the shell script instead of interactively prompting me for the new password. My code is below.

adduser $1 passwd $1 $2 $2

Answer 1

from "man 1 passwd":

   --stdin           This option is used to indicate that passwd should read the new           password from standard input, which can be a pipe. 

So in your case

adduser "$1" echo "$2" | passwd "$1" --stdin 

Your passwd command may not have a --stdin option: use the chpasswd utility instead, as suggested by ashawley.

If you use a shell other than bash, echo might not be a builtin command, and the shell will call /bin/echo. This is insecure because the password will show up in the process table and can be seen with tools like ps.

In this case, you should use another scripting language. Here is an example in Perl:

#!/usr/bin/perl -w open my $pipe, '|chpasswd' or die "can't open pipe: $!"; print {$pipe} "$username:$password"; close $pipe