我正在阅读有关 if 的 bash 示例,但有些示例是用单方括号编写的:
I'm reading bash examples about if but some examples are written with single square brackets:
if [ -f $param ] then #... fi其他方括号:
if [[ $? -ne 0 ]] then start looking for errors in yourlog fi有什么区别?
推荐答案单个 [] 是符合 posix shell 的条件测试.
Single [] are posix shell compliant condition tests.
Double [[]] 是标准 [] 的扩展,并被 bash 和其他 shell(例如 zsh、ksh)支持.它们支持额外的操作(以及标准的 posix 操作).例如:|| 代替 -o 和与 =~ 匹配的正则表达式.更完整的差异列表可以在 bash 手册部分关于条件构造.
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 [] 不支持条件表达式并且不需要可移植,请使用 [[]].
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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