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端末（OSX 10.6.6）で次のコマンドを試してみましたが、エラーが発生しました。誰もこれを解決する方法を知っていますか？gemでjsonをインストールできない
sudo gem install json
Building native extensions. This could take a while...
ERROR: Error installing json:
ERROR: Failed to build gem native extension.
/usr/local/bin/ruby extconf.rb
checking for ruby/re.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/bin/ruby
/usr/local/lib/ruby/1.9.1/mkmf.rb:368:in `try_do': The complier failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /usr/local/lib/ruby/1.9.1/mkmf.rb:452:in `try_cpp'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:834:in `block in have_header'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:693:in `block in checking_for'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:280:in `block (2 levels) in postpone'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:280:in `block in postpone'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:276:in `postpone'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:692:in `checking_for'
from /usr/local/lib/ruby/1.9.1/mkmf.rb:833:in `have_header'
from extconf.rb:17:in `'
Gem files will remain installed in /usr/local/lib/ruby/gems/1.9.1/gems/json-1.5.1 for inspection.
Results logged to /usr/local/lib/ruby/gems/1.9.1/gems/json-1.5.1/ext/json/ext/generator/gem_make.out
こんにちは、返信いただきありがとうございます。私はすでにXCodeをインストールしています（Snow LeopardのosxインストールCDが付属しています）。 – katsuya
macportsを使ってruby 1.9.1をインストールしましたか？ – Shiv
いいえ、私はrvmを使用しました。問題になることはありますか？ – katsuya