To get PostgreSQL 8.4 and the Pg gem installed from scratch on Mac OS X Leopard, and assuming you have XCode 3.1 and MacPorts 1.600 installed:

1. Install PostgreSQL from MacPort

   
   sudo port install postgresql84 postgresql84-server
   

2. Setup your database. PostgreSQL suggests the following commands:

   
   sudo mkdir -p /opt/local/var/db/postgresql84/defaultdb
   sudo chown postgres:postgres /opt/local/var/db/postgresql84/defaultdb
   sudo su postgres -c '/opt/local/lib/postgresql84/bin/initdb -D /opt/local/var/db/postgresql84/defaultdb'
   

3. Add /opt/local/lib/postgresql84/bin to your PATH. This usually goes in ~/.bash_profile or ~/.profile

4. Install the Ruby gem

   
   sudo gem install pg
   

5. Change the postgres user’s password

   
   sudo su - root
   passwd postgres
   

6. Create a helper script in your local bin directory

   
   ln -s /opt/local/etc/LaunchDaemons/org.macports.postgresql84-server/postgresql84-server.wrapper ~/local/bin/pgsql.server
   

7. To start and stop Postgres

   
   cd ~/local/bin
   pgsql.server start
   pgsql.server stop
   

8. Download pgAdmin (Optional)