gsub中的反斜杠（转义和反向引用） [英] Backslashes in gsub (escaping and backreferencing)

问题描述

请考虑以下代码段：

  puts'hello'.gsub（/.+/，'\0 \ \0 \\\0 \\\\0'）
  

这将打印（如在ideone.com上所见）：

  hello hello \0 \0 
  

非常惊讶，因为我希望看到像这样的东西：

  hello \0 \hello \\ 0 
  

我的论据是 \ 一个转义字符，所以你写 \\ 来获得一个字面反斜杠，因此 \\0 是一个字面反斜杠 \ 后跟 0 等等。显然这不是如何 gsub 正在解释它，所以有人可以解释发生了什么吗？

我需要做什么才能获得我想要的替换？ p >

解决方案

使用单引号而不是双引号时，转义是有限的：

  put'sinlge\\\
quote'
 putsdouble\\\
quote
  

\0是空字符（用于C确定字符串的结尾），其中 '\0'是\\0，因此'hello'.gsub（/。 + /，'\0'）和'hello'.gsub（/.+/，\\\0） return hello，但'hello'.gsub（/.+/，\0）返回 \000。现在'hello'.gsub（/.+/，'\\\0'）返回'hello'是红宝石试图处理程序员，而不是保持单引号和双引号之间的区别。实际上，这与 gsub 无关：'\0'==\\0和'\\0'==\\0。遵循这个逻辑，无论你想到什么，这是ruby看到其他字符串：'\\\\0'和 '\\\\\0'等于\\\\0，（打印时）给出你 \\0 。由于gsub使用 \x 来插入匹配号x，所以您需要一种方法来逃避 \x \\x 或其字符串表示形式：\\\\\x。因此，

  put'hello'.gsub（/ 。+ /，\\0 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ ）
  

确实导致

  hello \0 \hello \\0 
  

Consider the following snippet:

puts 'hello'.gsub(/.+/, '\0 \\0 \\\0 \\\\0')

This prints (as seen on ideone.com):

hello hello \0 \0

This was very surprising, because I'd expect to see something like this instead:

hello \0 \hello \\0

My argument is that \ is an escape character, so you write \\ to get a literal backslash, thus \\0 is a literal backslash \ followed by 0, etc. Obviously this is not how gsub is interpreting it, so can someone explain what's going on?

And what do I have to do to get the replacement I want above?

解决方案

Escaping is limited when using single quotes rather then double quotes:

puts 'sinlge\nquote'
puts "double\nquote"

"\0" is the null-character (used i.e. in C to determine the end of a string), where as '\0' is "\\0", therefore both 'hello'.gsub(/.+/, '\0') and 'hello'.gsub(/.+/, "\\0") return "hello", but 'hello'.gsub(/.+/, "\0") returns "\000". Now 'hello'.gsub(/.+/, '\\0') returning 'hello' is ruby trying to deal with programmers not keeping the difference between single and double quotes in mind. In fact, this has nothing to do with gsub: '\0' == "\\0" and '\\0' == "\\0". Following this logic, whatever you might think of it, this is how ruby sees the other strings: both '\\\0' and '\\\\0' equal "\\\\0", which (when printed) gives you \\0. As gsub uses \x for inserting match number x, you need a way to escape \x, which is \\x, or in its string representation: "\\\\x".

Therefore the line

puts 'hello'.gsub(/.+/, "\\0 \\\\0 \\\\\\0 \\\\\\\\0")

indeed results in

hello \0 \hello \\0

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