gem install compass not working - ruby-on-rails

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.