本文介绍了在子壳和当前壳两种不同环境下执行命令的区别。在子壳中执行命令时，创建了一个新的壳环境，命令在此环境中运行，变量赋值不会影响到父壳环境。而在当前壳中执行命令，则直接在当前环境中运行命令列表，不会创建新的子壳环境。
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( list )Placing a list of commands between parentheses causes a subshellenvironment to be created, and eachof the commands in list to be executed in that subshell. Since thelist is executed in a subshell, variable assignments do not remain ineffect after the subshell completes.
{}
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{ list; }Placing a list of commands between curly braces causes the list tobe executed in the current shell context. No subshell is created. The semicolon (or newline) following list is required.
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