db problems with Sinatra

http://www.postgresql.org/docs/9.1/static/manage-ag-createdb.html

This worked for me.$ export DATABASE_URL=postgres://localhost/activerecord_sinatra

createdb --help
createdb creates a PostgreSQL database.

Usage:
  createdb [OPTION]... [DBNAME] [DESCRIPTION]

Options:
  -D, --tablespace=TABLESPACE  default tablespace for the database
  -e, --echo                   show the commands being sent to the server
  -E, --encoding=ENCODING      encoding for the database
  -l, --locale=LOCALE          locale settings for the database
      --lc-collate=LOCALE      LC_COLLATE setting for the database
      --lc-ctype=LOCALE        LC_CTYPE setting for the database
  -O, --owner=OWNER            database user to own the new database
  -T, --template=TEMPLATE      template database to copy
  --help                       show this help, then exit
  --version                    output version information, then exit

Connection options:
  -h, --host=HOSTNAME          database server host or socket directory
  -p, --port=PORT              database server port
  -U, --username=USERNAME      user name to connect as
  -w, --no-password            never prompt for password
  -W, --password               force password prompt

By default, a database with the same name as the current user is created.

Report bugs to <pgsql-bugs@postgresql.org>._adapters/postgresql_adapter.rb:891:in `rescue in connect': FATAL:  database