Ruby %r{} 表达式 [英] The Ruby %r{ } expression

问题描述

模型中有一个字段

validates :image_file_name, :format => { :with => %r{\.(gif|jpg|jpeg|png)$}i

对我来说看起来很奇怪.我知道这是一个正则表达式.但我想:

It looks pretty odd for me. I am aware that this is a regular expression. But I would like:

• 了解它的确切含义.%r{value} 是否等于 /value/ ?
• 能够用普通的 Ruby 正则表达式运算符 /some regex/ 或 ~= 替换它.可能吗?

• to know what exactly it means. Is %r{value} equal to /value/ ?
• be able to replace it with normal Ruby regex operator /some regex/ or ~=. Is it possible?

推荐答案

%r{} 等同于 /.../ 符号，但允许您在您的正则表达式中有/"而不必转义它们:

%r{} is equivalent to the /.../ notation, but allows you to have '/' in your regexp without having to escape them:

%r{/home/user}

相当于:

/\/home\/user/

为了易读性，这只是一种语法商品.

This is only a syntax commodity, for legibility.

请注意，您几乎可以使用任何非字母字符对来代替{}".这些变体也同样有效:

Note that you can use almost any non-alphabetic character pair instead of '{}'. These variants work just as well:

%r!/home/user!
%r'/home/user'
%r(/home/user)

编辑 2:

请注意，%r{}x 变体忽略空格，使复杂的正则表达式更具可读性.GitHub 的 Ruby 风格指南中的示例:>

Note that the %r{}x variant ignores whitespace, making complex regexps more readable. Example from GitHub's Ruby style guide:

regexp = %r{
  start         # some text
  \s            # white space char
  (group)       # first group
  (?:alt1|alt2) # some alternation
  end
}x

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