gem install compass won't work - ruby

Question

When I try to install compass using sudo gem install compass it show me this :
Building native extensions. This could take a while...
ERROR: Error installing compass:
ERROR: Failed to build gem native extension.
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby -r ./siteconf20141125-86718-gjziv3-0.rb extconf.rb
checking for ffi.h... no
checking for ffi.h in /usr/local/include,/usr/include/ffi... no
checking for rb_thread_blocking_region()... no
checking for rb_thread_call_with_gvl()... no
checking for rb_thread_call_without_gvl()... no
checking for ffi_prep_cif_var()... no
creating extconf.h
creating Makefile
make clean
make
mkdir -p "/Library/Ruby/Gems/1.8/gems/ffi-1.9.6/ext/ffi_c"/libffi-i386; (if [ ! -f "/Library/Ruby/Gems/1.8/gems/ffi-1.9.6/ext/ffi_c"/libffi-i386/Makefile ]; then echo "Configuring libffi for i386"; cd "/Library/Ruby/Gems/1.8/gems/ffi-1.9.6/ext/ffi_c"/libffi-i386 && env CC=" xcrun cc" CFLAGS="-arch i386 " LDFLAGS="-arch i386" "/Library/Ruby/Gems/1.8/gems/ffi-1.9.6/ext/ffi_c/libffi"/configure --disable-static --with-pic=yes --disable-dependency-tracking --host=i386-apple-darwin > /dev/null; fi); env MACOSX_DEPLOYMENT_TARGET=10.4 make -C "/Library/Ruby/Gems/1.8/gems/ffi-1.9.6/ext/ffi_c"/libffi-i386
Configuring libffi for i386
configure: WARNING: if you wanted to set the --build type, don't use --host.
If a cross compiler is detected then cross compile mode will be used
configure: error: in `/Library/Ruby/Gems/1.8/gems/ffi-1.9.6/ext/ffi_c/libffi-i386':
configure: error: C compiler cannot create executables
See `config.log' for more details
make[1]: *** No targets specified and no makefile found. Stop.
make: *** ["/Library/Ruby/Gems/1.8/gems/ffi-1.9.6/ext/ffi_c"/libffi-i386/.libs/libffi_convenience.a] Error 2
make failed, exit code 2
Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/ffi-1.9.6 for inspection.
Results logged to /Library/Ruby/Gems/1.8/extensions/universal-darwin-11/1.8/ffi-1.9.6/gem_make.out
I have correctly install sass and xcode' tools but nothing change. I even try to upgrade ruby. What should I do?

Answer 1

It happens because you want to sudo install and probably environment variables are not configured to use your installed ruby, instead it uses the system ruby which probably is not what you want to use.
The easiest way to use Ruby on Mac is to install rbenv and ruby-build using homebrew.
To install homebrew just run this command which can be found on brew homepage:
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
To install rbenv and ruby-build you can run these commands which can be found on Github:
brew update
brew install rbenv ruby-build
Forgot to add that for sure, then you need to install a ruby version using rbenv and make it global.
rbenv install 2.1.5
rbenv global 2.1.5
And finally:
gem install compass
Just make sure that gem binary points to the version you've installed.
You can run gem env and checkout printed paths, if it doesn't point to newly installed ruby gem path, close the terminal and open a new one then install the gem.
Here is the first few lines of what's printed out on my machine:
RubyGems Environment:
- RUBYGEMS VERSION: 2.2.0
- RUBY VERSION: 2.1.0 (2013-12-25 patchlevel 0) [x86_64-darwin13.0]
- INSTALLATION DIRECTORY: /Users/jani/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0
....