为什么不是[[...]]之间进行引用删除？ [英] why quote removal isn't performed between [[ ... ]]?

问题描述

  $ bash的人
 

  

词的拆分和文件名扩展是不是[[和]]之间的单词进行;波浪线扩展，参数和变量扩展，算术扩展，命令替换，函数替换和引用的去除执行。

  $回声$ BASH_VERSION
4.2.10（1）-release
 

命令1

  $ [你好=〜他]]＆放大器;＆安培;回声是||回声NO
是
 

命令2

  $ [你好=〜他*]]＆功放;＆安培;回声是||回声NO
是
 

命令3

  $ [你好=〜]他。*]放;＆安培;回声是||回声NO
没有
 

为什么命令2和3是不同的？

解决方案

检查您的bash的版本。起价3.2版本中添加这种行为状态：

  

引用的字符串参数的[[命令的=〜运营商现在的力量
  串匹配，与其它模式匹配运算

我猜你正在使用bash> = 3.2版本为您的测试。

这就是原因，当你引用的常规前pression它做朴素简单的字符串，而不是正则表达式匹配匹配。

更新：如果您想正则表达式匹配里面的双引号，然后使用：

 禁用了javascript -s compat31
 

由于每本手册：

  

compat31

  
  

如果设置时，bash改变其行为到3.1版本
  对于引用参数的条件命令的=〜运营商。

这将导致您的命令，以不同的表现：

  [你好=〜他*。]]＆放大器;＆安培;回声是||回声NO
是
 

$ man bash

Word splitting and filename expansion are not performed on the words between the ‘[[’ and ‘]]’; tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process substitution, and quote removal are performed.

$ echo $BASH_VERSION
4.2.10(1)-release

command 1

$ [[ "hello" =~ "he"   ]] && echo YES || echo NO
YES

command 2

$ [[ "hello" =~  he.*  ]] && echo YES || echo NO
YES

command 3

$ [[ "hello" =~ "he.*" ]] && echo YES || echo NO
NO

Why command 2 and 3 are different?

解决方案

Check your bash version. Starting from version 3.2 this behavior was added that states:

Quoting the string argument to the [[ command's =~ operator now forces string matching, as with the other pattern-matching operators.

I guess you are using bash >= ver 3.2 for your test.

That's the reason when you quote the regular expression it is doing plain simple string matching instead of regex matching.

Update: If you want regex matching inside double quotes then use:

shopt -s compat31

As per the manual:

compat31

If set, bash changes its behavior to that of version 3.1 with respect to quoted arguments to the conditional command's =~ operator.

which causes your command to behave differently:

[[ "hello" =~ "he.*" ]] && echo YES || echo NO
YES

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