Cannot install pg gem in Mavericks with Postgres.app

You probably have the wrong path for --with-pg-config, check if it's actually there.

You can find the correct path to pg_config with:

find /Applications -name pg_config

In the latest Postgres.app Version the path is:

gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.5/bin/pg_config

In my case (running Postgres.app v9.3.4.2) it only seemed to work when prepending the environment architecture flags:

env ARCHFLAGS="-arch x86_64" gem install pg -- \--with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config 

Being on a brand new mac, here's what I had to do:

1. Install Xcode tools from the app store
2. Open Xcode tools and accept the license

3. Now run (hopefully a future-proofed command):

   version=$(ls /Applications/Postgres.app/Contents/Versions/ | tail -1)gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/Versions/$version/bin/pg_config .

If you have trouble, you can troubleshoot a bit by checking out the actual error in the mkmf.log which you can find by running (if using rvm):

cd ~/.rvm ; find . -name mkmf.log | grep pg