can't install postgres ruby gem [duplicate]

Question

I am having trouble install postgres on OSX mavericks. I have tried to follow the numerous guides on Stackoverflow with no luck. I installed the postgres.app and also postgres. I have found my pg_config file and tried this command:

gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config

But I am still getting this error

Building native extensions with: '--with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config .'
This could take a while...
ERROR:  Error installing pg:
ERROR: Failed to build gem native extension.

/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config .
Using config values from /Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config
checking for libpq-fe.h... yes
checking for libpq/libpq-fs.h... yes
checking for pg_config_manual.h... yes
checking for PQconnectdb() in -lpq... no
checking for PQconnectdb() in -llibpq... no
checking for PQconnectdb() in -lms/libpq... no
Can't find the PostgreSQL client library (libpq)
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
--with-pg
--without-pg
--with-pg-config
--with-pg-dir
--without-pg-dir
--with-pg-include
--without-pg-include=${pg-dir}/include
--with-pg-lib
--without-pg-lib=${pg-dir}/
--with-pqlib
--without-pqlib
--with-libpqlib
--without-libpqlib
--with-ms/libpqlib
--without-ms/libpqlib

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/pg-0.17.1 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-13/2.0.0/pg-0.17.1/gem_make.out

Answer 1

This also seems to be working:

Can't find the PostgreSQL client library (libpq)

$ sudo su

$ env ARCHFLAGS="-arch x86_64" gem install pg