关于这个问题，有很多话题，但我已经尝试了几乎所有的方法，都没有成功。
我使用的是 Mac OS X 10.9.4 Mavericks，我安装了 Postgres.app，并且它似乎运行良好。 sudo gem install pg 也可以正常工作：
Building native extensions. This could take a while...
Successfully installed pg-0.17.1
invalid options: -f fivefish
(invalid options are ignored)
Parsing documentation for pg-0.17.1
Done installing documentation for pg after 2 seconds
1 gem installed
但是当我尝试运行
bundle install时，我遇到了和其他人一样的错误。
我已经尝试过
bundle config build.pg --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config，然后运行bundle install我已经安装了Xcode命令行工具。
which psql返回/Applications/Postgres.app/Contents/Versions/9.3/bin/psqlwhich postgres返回/Applications/Postgres.app/Contents/Versions/9.3/bin/postgres
这里是bundle install的错误信息：
Gem::Ext::BuildError: 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 /var/folders/07/my1cl5xj7g9cknnp3y2zg_rh0000gn/T/bundler20140723-29399-1o0uzqn/pg-0.17.1/gems/pg-0.17.1 for inspection.
Results logged to /var/folders/07/my1cl5xj7g9cknnp3y2zg_rh0000gn/T/bundler20140723-29399-1o0uzqn/pg-0.17.1/extensions/universal-darwin-13/2.0.0/pg-0.17.1/gem_make.out
An error occurred while installing pg (0.17.1), and Bundler cannot continue.
Make sure that `gem install pg -v '0.17.1'` succeeds before bundling.