用Bash变量进行括号扩展-{0 .. $ foo} [英] Brace expansion with a Bash variable - {0..$foo}

问题描述

WEEKS_TO_SAVE=4
mkdir -p weekly.{0..$WEEKS_TO_SAVE}

给我一​​个名为Weekly的文件夹.{0..4}

gives me a folder called weekly.{0..4}

创建丢失的文件夹时，花括号扩展是否有秘密?

Is there a secret to curly brace expansion while creating folders I'm missing?

推荐答案

bash在variable expansion之前执行brace expansion，因此得到weekly.{0..4}.
由于结果是可预测且安全的(不信任用户输入)，因此您可以在情况下使用eval:

bash does brace expansion before variable expansion, so you get weekly.{0..4}.
Because the result is predictable and safe(Don't trust user input), you can use eval in your case:

$ WEEKS_TO_SAVE=4
$ eval "mkdir -p weekly.{0..$((WEEKS_TO_SAVE))}"

注释:

1. eval是邪恶的
2. 小心使用eval

1. eval is evil
2. use eval carefully

在这里，$((..))用于强制将变量评估为整数表达式.

Here, $((..)) is used to force the variable to be evaluated as an integer expression.

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