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 right answer for Mac users with Postgres.app is to build against the libpq provided with that package. For example, with the 9.4 release (current as of this writing), all you need is:

export CONFIGURE_ARGS="with-pg-include=/Applications/Postgres.app/Contents/Versions/9.4/include"
gem install pg

This will keep your pg gem in sync with exactly the version of PostgreSQL you have installed. Installing something from Homebrew is a waste in this case.