遇到 no such file to load -- mkmf 这个错误的解决办法

今天用gem安装gettext时，遇到了这个错误：

命令行提示：
Building native extensions.  This could take a while...
ERROR:  While executing gem ... (Gem::Installer::ExtensionBuildError)
    ERROR: Failed to build gem native extension.

ruby extconf.rb install gettext
extconf.rb:12:in `require': no such file to load -- mkmf (LoadError)
        from extconf.rb:12

原来，gem需要编译，但找不到文件mkmf,所以，要先安装ruby1.8-dev,这样就不会报错了。

命令行提示:

sudo apt-get install ruby1.8-dev