Bash中单方括号和双方括号之间的区别 [英] Difference between single and double square brackets in Bash

问题描述

我正在阅读关于的bash示例，如果但是一些示例是用单个方括号编写的：

I'm reading bash examples about if but some examples are written with single square brackets:

if [ -f $param ]
then
  #...
fi

其他双方括号：

if [[ $? -ne 0 ]]
then
    start looking for errors in yourlog
fi

有什么区别？

推荐答案

单 [] 是posix shell兼容条件测试。

Single [] are posix shell compliant condition tests.

Double [[]] 是标准<$ c $的扩展名c> [] 并受bash和其他shell支持（例如zsh，ksh）。它们支持额外的操作（以及标准的posix操作）。例如： || 而不是 -o 和正则表达式匹配 =〜。有关条件的 bash手册部分可以找到更完整的差异列表构造。

Double [[]] are an extension to the standard [] and are supported by bash and other shells (e.g. zsh, ksh). They support extra operations (as well as the standard posix operations). For example: || instead of -o and regex matching with =~. A fuller list of differences can be found in the bash manual section on conditional constructs.

只要您希望脚本可以跨shell移植，请使用 [] 。如果您希望 [] 不支持条件表达式，请使用 [[]] ，并且不需要是可移植的。

Use [] whenever you want your script to be portable across shells. Use [[]] if you want conditional expressions not supported by [] and don't need to be portable.

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