我正在尝试按照 rails 站点上的说明在 OS X Yosemite 10.10.5 上安装 Ruby on Rails v5：
http://railsapps.github.io/installrubyonrails-mac.html
当我运行这个：
sudo gem install rails --version 5.0.0 --no-ri --no-rdoc
我收到错误ERROR: Failed to build gem native extension。以下是我的命令行上可能有用的部分输出：
current directory: /Users/me/.rvm/rubies/ruby-2.3.0/lib/ruby/gems/2.3.0/gems/nokogiri-1.6.8/ext/nokogiri
[...]
Running 'compile' for libxml2 2.9.4... ERROR, review '/Users/me/.rvm/rubies/ruby-2.3.0/lib/ruby/gems/2.3.0/gems/nokogiri-1.6.8/ext/nokogiri/tmp/x86_64-apple-da
rwin14.5.0/ports/libxml2/2.9.4/compile.log' to see what happened. Last lines are:
[...]
1 error generated.
make[2]: *** [xmlIO.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
========================================================================
*** extconf.rb failed ***
Could not create Makefile due …我知道:
preg_replace('<br\s*\/?>', '', $string);
将删除$ string中的所有br标签...
我们怎样才能删除所有<br><br/><br />标签,只要它们位于$ string的最开头？(在我的例子中,$ string是带有各种标签的HTML代码......)