按名称间接查找 shell 变量 [英] Lookup shell variables by name, indirectly

问题描述

假设我有一个变量的名称存储在另一个变量中:

myvar=123变量名=我的变量

现在，我想通过使用 $varname 变量来获得 123.有没有直接的方法?我发现没有这样的 bash 内置用于按名称查找，所以想出了这个:

function var { v=$$1";评估回声"$v;}

所以

var $varname # 给出 123

最后看起来还不错，但我想知道我是否遗漏了一些更明显的东西.

解决方案

来自 bash 手册页:

${!varname}

<块引用>

如果参数的第一个字符是感叹号，则级别为变量间接引入.Bash 使用由参数的其余部分形成的变量的值作为变量的名称；这个变量然后被扩展，这个值被用于其余的替换，而不是参数本身的值.这是称为间接扩展.

Let's say I have a variable's name stored in another variable:

myvar=123
varname=myvar

Now, I'd like to get 123 by just using $varname variable. Is there a direct way for that? I found no such bash builtin for lookup by name, so came up with this:

function var { v="$$1"; eval "echo "$v; }

so

var $varname  # gives 123

Which doesn't look too bad in the end, but I'm wondering if I missed something more obvious.

解决方案

From the man page of bash:

${!varname}

If the first character of parameter is an exclamation point, a level of variable indirection is introduced. Bash uses the value of the variable formed from the rest of parameter as the name of the variable; this variable is then expanded and that value is used in the rest of the substitution, rather than the value of parameter itself. This is known as indirect expansion.

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