Bash 条件中括号和括号之间的区别 [英] Difference between parentheses and brackets in Bash conditionals

问题描述

在学习一些关于 bash 的同时，我来看看四种使用 if 语句的方法:

While learning a bit about bash, I come to see four types of ways of working with if statements:

• 单括号 - ( ... )
• 双括号 - (( ... ))
• 单方括号 - [ ... ]
• 双方括号 - [[ ... ]]

bash 中括号和方括号有什么区别.

What is the difference between Parenthesis and Square Brackets in bash.

推荐答案

您列出的测试:

• 单括号 - ( ... ) 正在创建一个子外壳
• 双括号 - (( ... )) 用于算术运算
• 单方括号 - [ ... ] 是 POSIX test
的语法
• 双方括号 - [[ ... ]] 是 bash 条件表达式的语法(类似于 test 但更强大)

• Single Parenthesis - ( ... ) is creating a subshell
• Double Parenthesis - (( ... )) is for arithmetic operation
• Single Square Bracket - [ ... ] is the syntax for the POSIX test
• Double Square Brackets - [[ ... ]] is the syntax for bash conditional expressions (similar to test but more powerful)

并非详尽无遗，您可以使用布尔逻辑

are not exhaustive, you can use boolean logic

if command; then ...

也是，因为命令有退出状态.在 bash 中，0 是 true 并且 > 0 是 false.

too, because the commands have exit status. In bash, 0 is true and > 0 is false.

你可以看到这样的退出状态:

You can see the exit status like this :

command
echo $?

见:

http://wiki.bash-hackers.org/syntax/basicgrammar
http://wiki.bash-hackers.org/syntax/arith_expr
http://mywiki.wooledge.org/BashGuide/TestsAndConditionals

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