Programmatically changing passwords

[David Leangen <postgres@xxxxxxxxxxx>]

Hello!

I am trying to build an RPM package that will put my Postgres  
installation into a known (usable) state, without requiring any  
interaction.

To this effect, I need to do the following:

1. set password for superuser
2. createuser user
3. createdb -O user dbname


No problems with (3) above. But for (1) and (2), how can I set the  
passwords programmatically, since createuser does not let me do this  
(requires interactive prompt from user)?


Thank you!