Can't find the 'libpq-fe.h header when trying to install pg gem

Question

I am using the Ruby on Rails 3.1 pre version. I like to use PostgreSQL, but the problem is installing the pg gem. It gives me the following error:

Answer 1

The location of libpq-fe.h depends on where your PostgreSQL install is (which depends on how you installed it). Use locate (http://en.wikipedia.org/wiki/Locate_%28Unix%29) to find the libpq-fe.h file on your machine. If it exists, it will be in the include directory of your PostgreSQL install.

$ locate libpq-fe.h
/Library/PostgreSQL/9.1/include/libpq-fe.h

The bin directory, which contains pg_config, will be in the same directory as the include directory. As the error suggests, use the --with-pg-config option to install the gem:

$ gem install pg --with-pg-config="/Library/PostgreSQL/9.1/bin/pg_config"

Note that you may need to run updatedb if you have never used locate or if you haven't updated since installing PostgreSQL.