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
Ubuntu 20.10 (pop!_os)
Ruby 2.7.2
Rails 3.1.0
Postgresql 12
卸载后重新安装postgresql-client libpq5 libpq-dev
sudo apt remove postgresql-client libpq5 libpq-dev
sudo apt install postgresql-client libpq5 libpq-dev
然后再次安装pg gem，指向/usr/lib，找到pg库:
gem install pg -- --with-pg-lib=/usr/lib
输出(你应该在前面的命令之后看到的):
Building native extensions with: '--with-pg-lib=/usr/lib'
This could take a while...
Successfully installed pg-1.2.3
Parsing documentation for pg-1.2.3
Installing ri documentation for pg-1.2.3
Done installing documentation for pg after 1 seconds
1 gem installed
Gem应该安装，然后继续正常的bundle安装或更新:
bundle
bundle install
bundle update
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
