Password change in Linux is done thru "passwd" command, but the bottleneck on this is interactive. Particularly it'll be difficult to handle thru scripting.
Here is the one liner for creation of useradd and changing its password
useradd -u 5313 -g dba -d /home/ajit -m ajit
To change the password for the user ajit,
echo "ajit:newpass"|chpasswd
These password can also be done thru encryption.