如何在Bash中使用read命令? [英] How to use the read command in Bash?

问题描述

当我尝试像这样在Bash中使用read命令时:

When I try to use the read command in Bash like this:

echo hello | read str
echo $str

没有回声，而我认为str应该包含字符串hello.有人可以帮我了解这种行为吗?

Nothing echoed, while I think str should contain the string hello. Can anybody please help me understand this behavior?

推荐答案

您的脚本命令中的read很好.但是，您在管道中执行它，这意味着它在子外壳中，因此，它读取的变量在父外壳中不可见.您可以

The read in your script command is fine. However, you execute it in the pipeline, which means it is in a subshell, therefore, the variables it reads to are not visible in the parent shell. You can either

• 也将脚本的其余部分移动到子外壳中:

• move the rest of the script in the subshell, too:

echo hello | { read str
  echo $str
}

或使用命令替换从子shell中获取变量的值

or use command substitution to get the value of the variable out of the subshell

str=$(echo hello)
echo $str

或更复杂的示例(抓取ls的第二个元素)

or a slightly more complicated example (Grabbing the 2nd element of ls)

str=$(ls | { read a; read a; echo $a; })
echo $str

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