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

在学习一些有关 bash 的问题时，我来了解使用 if 语句的四种类型的方法:

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-(...)正在创建子shell
• 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 ，但功能更强大)

• 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)

并不详尽，可以使用布尔逻辑

if command; then ...

也是，因为命令具有退出状态.在 bash 中， 0 为 true ，> 0 为 false .

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

您可以看到这样的退出状态:

You can see the exit status like this :

command
echo $?

请参阅:

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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