ruby on rails gem install pg时无法安装

gem install pg -v '0.18.2'
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
    ERROR: Failed to build gem native extension.

    current directory: /Users/bevan/.rvm/gems/ruby-2.3.0/gems/pg-0.18.2/ext
/Users/bevan/.rvm/rubies/ruby-2.3.0/bin/ruby -r ./siteconf20160226-49308-30rbgs.rb extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
 --with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** 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
    --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=/Users/bevan/.rvm/rubies/ruby-2.3.0/bin/$(RUBY_BASE_NAME)
    --with-pg
    --without-pg
    --enable-windows-cross
    --disable-windows-cross
    --with-pg-config
    --without-pg-config
    --with-pg_config
    --without-pg_config
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Users/bevan/.rvm/gems/ruby-2.3.0/extensions/x86_64-darwin-15/2.3.0/pg-0.18.2/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Users/bevan/.rvm/gems/ruby-2.3.0/gems/pg-0.18.2 for inspection.
Results logged to /Users/bevan/.rvm/gems/ruby-2.3.0/extensions/x86_64-darwin-15/2.3.0/pg-0.18.2/gem_make.out

当出现如上的错误的时候，解决方法如下

ubuntu:

1.  sudo apt-get install libpq-dev

2.  gem install pg

mac:

1. brew install postgresql
2. gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.4/bin/pg_config