使用gem install rails出現(xiàn)下面的信息：
Building native extensions. This could take a while...
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.
/Users/catcoder/.rvm/rubies/ruby-2.1.3/bin/ruby -r ./siteconf20150512-38048-1seathp.rb extconf.rb
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
The file "/usr/include/iconv.h" is missing in your build environment,
which means you haven't installed Xcode Command Line Tools properly.
To install Command Line Tools, try runningxcode-select --installon
terminal and follow the instructions. If it fails, open Xcode.app,
select from the menu "Xcode" - "Open Developer Tool" - "More Developer
Tools" to open the developer site, download the installer for your OS
version and run it.
*** 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
--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=/Users/catcoder/.rvm/rubies/ruby-2.1.3/bin/ruby
--help
--clean
--use-system-libraries
--enable-static
--disable-static
--with-zlib-dir
--without-zlib-dir
--with-zlib-include
--without-zlib-include=${zlib-dir}/include
--with-zlib-lib
--without-zlib-lib=${zlib-dir}/lib
--enable-cross-build
--disable-cross-build
extconf failed, exit code 1
Gem files will remain installed in /Users/catcoder/.rvm/rubies/ruby-2.1.3/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.6.2 for inspection.
Results logged to /Users/catcoder/.rvm/rubies/ruby-2.1.3/lib/ruby/gems/2.1.0/extensions/x86_64-darwin-14/2.1.0/nokogiri-1.6.6.2/gem_make.out
安裝上方的說(shuō)明，輸入xcode-select --install,會(huì)彈出窗體，安裝xcode命令行編譯工具长已，等待安裝完成锌杀，重新安裝rails笙蒙，可以正常進(jìn)行。
等待一段時(shí)間安裝完畢，執(zhí)行：
rails -v
返回：Rails 4.2.1，表明安裝成功茉继。
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