bash – 为什么在[[…]]之间不执行引用删除？

发布时间：2020-12-15 18:57:53 所属栏目：安全来源：网络整理

导读：$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

$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

命令1

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

命令2

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

命令3

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

为什么命令2和3不同？

检查你的bash版本.从版本3.2开始,添加了以下状态：

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

我猜你正在使用bash> = ver 3.2进行测试.

这就是你引用正则表达式的原因,它正在进行简单的字符串匹配而不是正则表达式匹配.

更新：如果你想在双引号内匹配正则表达式,那么使用：

shopt -s compat31

根据手册：

compat31

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

这会导致您的命令行为不同：

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

（编辑：李大同）

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