gem install compass not working

Question

having trouble running the line gem install compass in terminal. It's returning the following error. Is anyone able to help out with this problem?

ERROR: Error installing compass: ERROR: Failed to build gem native extension.

    /usr/local/rvm/rubies/ruby-1.9.3-p392/bin/ruby -r ./siteconf20150225-51908-cfetpz.rb extconf.rb
checking for ffi.h... *** 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=/usr/local/rvm/rubies/ruby-1.9.3-p392/bin/ruby
  --with-ffi_c-dir
  --without-ffi_c-dir
  --with-ffi_c-include
  --without-ffi_c-include=${ffi_c-dir}/include
  --with-ffi_c-lib
  --without-ffi_c-lib=${ffi_c-dir}/lib
  --with-libffi-config
  --without-libffi-config
  --with-pkg-config
  --without-pkg-config
/usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:381:in

try_do': The compiler failed to generate an executable file. (RuntimeError) You have to install development tools first. from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:506:in try_cpp' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:931:in block in have_header' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:790:in block in checking_for' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:284:in block (2 levels) in postpone' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:254:in open' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:284:in block in postpone' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:254:in open' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:280:in postpone' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:789:in checking_for' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:930:in have_header' from extconf.rb:16:in'

extconf failed, exit code 1

Gem files will remain installed in /usr/local/rvm/gems/ruby-1.9.3-p392/gems/ffi-1.9.6 for inspection.
Results logged to /usr/local/rvm/gems/ruby-1.9.3-p392/extensions/x86_64-darwin-10/1.9.1-static/ffi-1.9.6/gem_make.out

Answer 1

The error you're getting is

(RuntimeError)
   You have to install development tools first.

If you're on OS X (my best guess from the output) you need to install the Xcode developer tools first. You can do this with the command: xcode-select --install.