使用 Bash 变量支持扩展 - {0..$foo}
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Brace expansion with a Bash variable - {0..$foo}
提问by xref
WEEKS_TO_SAVE=4
mkdir -p weekly.{0..$WEEKS_TO_SAVE}
gives me a folder called weekly.{0..4}
给我一个名为每周的文件夹。{0..4}
Is there a secret to curly brace expansion while creating folders I'm missing?
在创建我丢失的文件夹时是否有花括号扩展的秘密？
采纳答案by kev
bashdoes brace expansionbefore variable expansion, so you get weekly.{0..4}.
Because the result is predictable and safe(Don't trust user input), you can use evalin your case:
bashbrace expansion之前没有variable expansion，所以你得到weekly.{0..4}。
因为结果是可预测且安全的（不要相信用户输入），所以您可以eval在您的情况下使用：
$ WEEKS_TO_SAVE=4
$ eval "mkdir -p weekly.{0..$((WEEKS_TO_SAVE))}"
note:
注意：
evalis evil- use
evalcarefully
eval是邪恶的eval小心使用
Here, $((..))is used to force the variable to be evaluated as an integer expression.
在这里，$((..))用于强制将变量计算为整数表达式。
回答by anubhava
Curly braces don't support variables in BASH, you can do this:
花括号不支持 BASH 中的变量，你可以这样做：
for (( c=0; c<=WEEKS_TO_SAVE; c++ ))
do
mkdir -p weekly.${c}
done
回答by jfg956
Another way of doing it without eval and calling mkdir only once:
另一种不使用 eval 并且只调用一次 mkdir 的方法：
WEEKS_TO_SAVE=4
mkdir -p $(seq -f "weekly.%.0f" 0 $WEEKS_TO_SAVE)
回答by amit_g
Brace expansiondoes not support it. You will have to do it using a loop.
Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result. It is strictly textual. Bash does not apply any syntactic interpretation to the context of the expansion or the text between the braces. To avoid conflicts with parameter expansion, the string ‘${' is not considered eligible for brace expansion
大括号扩展在任何其他扩展之前执行，并且其他扩展所特有的任何字符都保留在结果中。它是严格的文本。Bash 不对扩展的上下文或大括号之间的文本应用任何句法解释。为避免与参数扩展冲突，字符串 '${' 不被视为符合大括号扩展的条件
.
.
回答by SiegeX
If you happen to have zshinstalled on your box, your code as written willwork with Z-shell if you use #!/bin/zshas your interpreter:
如果您碰巧zsh安装在您的机器上，如果您将其用作解释器，那么您编写的代码将与 Z-shell 一起使用#!/bin/zsh：
Example
例子
$ WEEKS_TO_SAVE=4
$ echo {0..$WEEKS_TO_SAVE}
0 1 2 3 4
