Ruby has become such a key element in modern web development that data access to PostgreSQL from Ruby is almost a a required element. Ruby has a built in tool for installing modules that is well known in Gem. The gem install tool is easy, but sometimes requires a little bit of massaging. Two of the popular PostgreSQL gems are postgres and pg. Both can be installed with gem using this PostgreSQL installation:
postgres:
sudo gem install postgres -- --with-pgsql-dir=/Library/PostgreSQL
pg:
sudo gem install pg -- --with-pg-dir=/Library/PostgreSQL