单引号内的内容,ruby会原样输出

双引号内的内容,ruby会解析

我们看个简单的例子,针对字符串      #{foo}test     我们分别用单引号核双引号操作

 '#{foo}test'

=> "\#{foo}test"

"#{foo}test"

NameError: undefined local variable or method `foo' for main:Object
        from (irb):4
        from C:/Ruby192/bin/irb:12:in `<main>'

显而易见, 双引号对字符串内的#进行了解析, 导致ruby认为foo是个方法,出错.

类似的, %W %Q 相当于双引号,   %w %q 相当于单引号.

转载: http://simpleror.wordpress.com/2009/03/15/q-q-w-w-x-r-s/  

%Q

This is an alternative for double-quoted strings, when you have more quote characters in a string.Instead of putting backslashes in front of them, you can easily write:
>> %Q(Joe said: "Frank said: "#{what_frank_said}"")
=> "Joe said: "Frank said: "Hello!"""


The parenthesis “(…)” can be replaced with any other non-alphanumeric characters and non-printing characters (pairs), so the following commands are equivalent:
>> %Q!Joe said: "Frank said: "#{what_frank_said}""!
>> %Q[Joe said: "Frank said: "#{what_frank_said}""]
>> %Q+Joe said: "Frank said: "#{what_frank_said}""+

You can use also:
>> %/Joe said: "Frank said: "#{what_frank_said}""/
=> "Joe said: "Frank said: "Hello!"""

%q

Used for single-quoted strings.The syntax is similar to %Q, but single-quoted strings are not subject to expression substitution or escape sequences.
>> %q(Joe said: 'Frank said: '#{what_frank_said} ' ')
=> "Joe said: 'Frank said: '\#{what_frank_said} ' '"


%W

Used for double-quoted array elements.The syntax is similar to %Q
>> %W(#{foo} Bar Bar\ with\ space)
=> ["Foo", "Bar", "Bar with space"]


%w

Used for single-quoted array elements.The syntax is similar to %Q, but single-quoted elements are not subject to expression substitution or escape sequences.
>> %w(#{foo} Bar Bar\ with\ space)
=> ["\#{foo}", "Bar", "Bar with space"]


%x

Uses the ` method and returns the standard output of running the command in a subshell.The syntax is similar to %Q.
>> %x(echo foo:#{foo})
=> "foo:Foo\n"


%r

Used for regular expressions.The syntax is similar to %Q.
>> %r(/home/#{foo})
=> "/\\/home\\/Foo/"


%s

Used for symbols.It’s not subject to expression substitution or escape sequences.
>> %s(foo)
=> :foo
>> %s(foo bar)
=> :"foo bar"
>> %s(#{foo} bar)
=> :"\#{foo} bar"