Create database from command line

Change the user to postgres :

su - postgres

Create User for Postgres (in the shell and NOT with psql)

$ createuser testuser

Create Database (same)

$ createdb testdb

Acces the postgres Shell

psql ( enter the password for postgressql)

Provide the privileges to the postgres user

$ alter user testuser with encrypted password 'qwerty';
$ grant all privileges on database testdb to testuser;

createdb is a command line utility which you can run from bash and not from psql. To create a database from psql, use the create database statement like so:

create database [databasename];

Note: be sure to always end your SQL statements with ;

Try:

sudo -u postgres psql -c 'create database test;'