转：Ruby 里的 %Q, %q, %W, %w, %x, %r, %s, %i

%Q

用于替代双引号的字符串. 当你需要在字符串里放入很多引号时候, 可以直接用下面方法而不需要在引号前逐个添加反斜杠 (\")

>> %Q(Joe said: "Frank said: "#{what_frank_said}"")
=> "Joe said: "Frank said: "Hello!"""
(...)也可用其他非数字字母的符号或成对的符号代替, 诸如[...], !...!, +...+,{...}, <...>等.

以下写法全部与上面等效:

>> %Q!Joe said: "Frank said: "#{what_frank_said}""!
>> %Q[Joe said: "Frank said: "#{what_frank_said}""]
>> %Q+Joe said: "Frank said: "#{what_frank_said}""+
除此之外还可省略Q写作:

>> %/Joe said: "Frank said: "#{what_frank_said}""/
=> "Joe said: "Frank said: "Hello!""" 
%q

与%Q类似, 但是表示的是单引号字符串

>> %q(Joe said: 'Frank said: '#{what_frank_said} ' ')
=> "Joe said: 'Frank said: '\#{what_frank_said} ' '"    
%W

语法近似于%Q, 用于表示其中元素被双引号括起的数组.

>> %W(#{foo} Bar Bar\ with\ space)
=> ["Foo", "Bar", "Bar with space"] 
%w

用于表示其中元素被单引号括起的数组. 比较奇怪的是\(斜杠空格)会被转化成(空格), 但是其他的内容不会.

>> %w(a b c\ d \#e #{1}f)
=> ["a", "b", "c d", "\\#e", "\#{1}f"]
%x

使用`方法执行一段shell脚本并返回标准输出内容.

>> %x(echo foo:#{foo})
=> "foo:Foo\n"    
%r

语法近似于%Q, 用于正则表达式.

>> %r(/home/#{foo})
 => "/\\/home\\/Foo/"     
%s

用于表示symbol, 但是不会对其中表达式等内容进行转化

>> %s(foo)
=> :foo
>> %s(foo bar)
=> :"foo bar"
>> %s(#{foo} bar)
=> :"\#{foo} bar"
%i

Ruby 2.0 之后引入的语法, 用于生成一个symbol数组

2.0.0p247 :014 > %i(a b c)
=> [:a, :b, :c]