Ever since upgrading to Yosemite, I get this error trying to build anything that includes ruby.h:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby.h:33:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby/ruby.h:24:10: fatal error: 'ruby/config.h' file not found
#include "ruby/config.h"
^
1 error generated.
make[1]: *** [objects/if_ruby.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make: *** [first] Error 2
And sure enough, /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby/config.h is indeed missing.
$ ls -laF /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby/
total 72
drwxr-xr-x 21 root wheel 714 Jul 29 21:56 ./
drwxr-xr-x 5 root wheel 170 Jul 29 21:56 ../
drwxr-xr-x 7 root wheel 238 Jul 29 21:56 backward/
-rw-r--r-- 2 root wheel 3360 Sep 21 15:25 debug.h
-rw-r--r-- 2 root wheel 5553 Sep 21 15:25 defines.h
-rw-r--r-- 2 root wheel 881 Sep 21 15:25 digest.h
-rw-r--r-- 2 root wheel 7628 Sep 21 15:25 dl.h
-rw-r--r-- 2 root wheel 14123 Sep 21 15:25 encoding.h
-rw-r--r-- 2 root wheel 32904 Sep 21 15:25 intern.h
-rw-r--r-- 2 root wheel 5869 Sep 21 15:25 io.h
-rw-r--r-- 2 root wheel 4522 Sep 21 15:25 missing.h
-rw-r--r-- 2 root wheel 37617 Sep 21 15:25 oniguruma.h
-rw-r--r-- 2 root wheel 1502 Sep 21 15:25 re.h
-rw-r--r-- 2 root wheel 890 Sep 21 15:25 regex.h
-rw-r--r-- 2 root wheel 49734 Sep 21 15:25 ruby.h
-rw-r--r-- 2 root wheel 4651 Sep 21 15:25 st.h
-rw-r--r-- 2 root wheel 374 Sep 21 15:25 subst.h
-rw-r--r-- 2 root wheel 1102 Sep 21 15:25 thread.h
-rw-r--r-- 2 root wheel 2139 Sep 21 15:25 util.h
-rw-r--r-- 2 root wheel 1968 Sep 21 15:25 version.h
-rw-r--r-- 2 root wheel 1794 Sep 21 15:25 vm.h
Did the install accidentally a file? Does Yosemite just ship with a busted Ruby header file set?
What's the best way to fix this? Can I just unpack the source code in there to get the right headers?
One note on this: I ran into this problem after upgrading to "OS X El Capitan". I installed the command line tools by running 'xcode-select --install'. After that, my ruby build environment started working again.
For those who already had Xcode installed from the Apple developers site, running xcode-select --install doesn't work, since it will say that Xcode is already installed (Xcode already comes with the CommandLineTools bundled).
In my case, I fixed it by downloading the corresponding CommandLineTools from the same place, executing it, then going to /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg and executing it too.
cd /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby
sudo ln -s ../universal-darwin15/ruby/config.h ./config.h
updates Nicholas Tsipanov's answer from 2014-10-18.
I got the same error, but installed "Command Line Tools (OS X 10.10) for Xcode - Xcode 6.1" and installing worked fine after that.
If you use Homebrew, brew install ruby is a fast workaround (it gets you a brand new ruby installation distinct from the one from Xcode).
Try this:
cd /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby
sudo ln -s ../universal-darwin13/ruby/config.h ./config.h
Xcode got messed up in the upgrade somehow.
I opened Xcode (which I never do otherwise) and it complained about all sorts of missing components. So I let it go ahead and fix itself, and now all is well.
Props to CDub in the comments on OP for pointing to this as a potential source of weirdness.
Fixed by pointing to correct path for Xcode developer tools.
Error before (Note the path to Xcode711.app instead of Xcode.app)
/Applications/Xcode711.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby/ruby.h:24:10:
Ran
sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
来源：https://stackoverflow.com/questions/26434642/yosemite-upgrade-broke-ruby-h