展开字符串的ENV变量，运行命令并存储在变量中? [英] Expand ENV variable of a string, run command and store in variable?

问题描述

如何扩展变量，运行该命令并将输出存储到变量?

How can I expand a variable, run that command and store output to variable?

通常您会这样做

var="$(echo string)"

但是我想要这个

envString='echo $stringToEcho'
stringToEcho="hello world"
var="$(${envString})"` 

，但其中的美元符号不会扩展.我需要运行存储在变量中的命令，并将输出存储到另一个变量.

but the dollar sign inside doesn't expand. I need to run a command stored in a variable and store the output to another variable.

推荐答案

如果您的字符串包含被编写为eval安全的内容:

If your string contains content which was written to be eval-safe:

envString="echo string"
var=$(eval "$envString")

...即使引用正确也可以使用，即使引用正确:

...which will work even if it includes variable references, if quoting correctly:

envString='echo "$someVar"'  # use single-quotes here to avoid premature expansion!
someVar='hello world'
var=$(eval "$envString")

但是，如果您的字符串包含通过扩展变量而未使用printf %q安全地转义包含的任何变量而生成的内容，则请勿这样做.

However, if your string contains contents generated by expanding variables without using printf %q to safely escape any variables contained, do not do this.

参考:

• BashFAQ#50 (我正在尝试将命令放入变量中，但是复杂的案例总是失败！)
• BashFAQ#48 (评估命令和安全性问题").

• BashFAQ #50 ("I'm trying to put a command in a variable, but the complex cases always fail!")
• BashFAQ #48 ("Eval command and security issues").

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