我尝试使用宝石安装pg，但它似乎不工作。
Gem install pg给出这个错误
Temporarily enhancing PATH to include DevKit...
Building native extensions. This could take a while...
ERROR: Error installing pg:
ERROR: Failed to build gem native extension.
C:/Ruby/bin/ruby.exe 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
--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=C:/Ruby/bin/ruby
--with-pg
--without-pg
--with-pg-dir
--without-pg-dir
--with-pg-include
--without-pg-include=${pg-dir}/include
--with-pg-lib
--without-pg-lib=${pg-dir}/lib
--with-pg-config
--without-pg-config
--with-pg_config
--without-pg_config
Gem files will remain installed in C:/Ruby/lib/ruby/gems/1.8/gems/pg-0.10.1 for
inspection.
Results logged to C:/Ruby/lib/ruby/gems/1.8/gems/pg-0.10.1/ext/gem_make.out
不管你运行的是什么操作系统，都要查看“Makefile”的日志文件，看看发生了什么，而不是盲目地安装东西。
在我的例子中，MAC OS，日志文件在这里:
/Users/za/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/pg-1.0.0/mkmf.log
日志提示无法创建make文件，原因如下:
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers
在mkmf.log中，您将看到它无法找到完成构建所需的库。
checking for pg_config... no
Can't find the 'libpq-fe.h header
blah blah
运行“brew install postgresql”后，我可以看到所有需要的库都在那里:
za:myapp za$ cat /Users/za/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/pg-1.0.0/mkmf.log | grep yes
find_executable: checking for pg_config... -------------------- yes
find_header: checking for libpq-fe.h... -------------------- yes
find_header: checking for libpq/libpq-fs.h... -------------------- yes
find_header: checking for pg_config_manual.h... -------------------- yes
have_library: checking for PQconnectdb() in -lpq... -------------------- yes
have_func: checking for PQsetSingleRowMode()... -------------------- yes
have_func: checking for PQconninfo()... -------------------- yes
have_func: checking for PQsslAttribute()... -------------------- yes
have_func: checking for PQencryptPasswordConn()... -------------------- yes
have_const: checking for PG_DIAG_TABLE_NAME in libpq-fe.h... -------------------- yes
have_header: checking for unistd.h... -------------------- yes
have_header: checking for inttypes.h... -------------------- yes
checking for C99 variable length arrays... -------------------- yes
@温菲尔德说:
pg gem需要绑定postgresql客户端库。这个错误通常意味着它找不到你的Postgres库。要么你没有安装它们，要么你可能需要传递——with-pg-dir=到你的gem安装中。
不仅如此，您只需要——with-pg-config=来安装它。
在Mac上
如果你碰巧也通过mac上的website bundle安装了postgres，它应该在/Applications/ postgres .app/Contents/Versions/9.3/bin这样的地方。
所以，你要么在gem install中传递它:
gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config
或者正确地设置了PATH。因为这可能太多了，临时设置PATH:
export PATH=%PATH:/Applications/Postgres.app/Contents/Versions/9.3/bin/
我必须在CentOS 5.8上这样做。运行捆绑包安装一直导致问题，因为我不能强制它使用特定的PG版本。
我也不能删除postgresql postgresql-devel，因为依赖关系的问题(它会删除php, http等)
解决方案?临时打乱$PATH以优先更新pgsql而不是默认pgsql:
export PATH=/usr/pgsql-9.2/bin:$PATH
bundle install
基本上，使用上面的命令，它会在/usr/bin/pg_config之前查看/usr/pgsql-9.2/bin/pg_config
