Bash中$()和()之间的区别 [英] Difference between $() and () in Bash

问题描述

当我键入ls -l $(echo file)时，将括号中的输出(这只是简单的回显)输出并传递给外部ls -l命令.等同于简单的ls -l file.

When I type ls -l $(echo file) output from bracket (which is just simple echo'ing) is taken and passed to external ls -l command. It equals to simple ls -l file.

当我键入ls -l (echo file)时，出现错误，因为不能将()嵌套在外部命令中.

When I type ls -l (echo file) we have error because one cannot nest () inside external command.

有人可以帮助我了解$()和()之间的区别吗?

Can someone help me understand the difference between $() and () ?

推荐答案

$(cmd)将cmd的结果替换为字符串，而(cmd; cmd)在子进程中运行命令列表.

$(cmd) substitutes the result of cmd as a string, whereas (cmd; cmd) run a list of commands in a subprocess.

如果要将一个或多个命令的输出放入变量中，请使用$(cmd)形式.

If you want to put the output of one or more commands into a variable use the $( cmd ) form.

但是，如果您要运行多个命令并将它们视为一个单元 使用()表单.

However if you want to run a number of commands and treat them as a single unit use the () form.

当您想在后台运行一组命令时，后者非常有用:

The latter is useful when you want to run a set of commands in the background:

(git pull; make clean; make all) &

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