解释 bash 中数组长度的 ${#arrayname[@]} 语法? [英] Explain ${#arrayname[@]} syntax for array length in bash?

问题描述

我知道可以通过执行 ${#arrayname[@]} 在 bash 中获得数组的长度.

I know that one can get the length of an array in bash by doing ${#arrayname[@]}.

我的问题是:这只是我必须记住的东西，还是可以将这种语法分解为可以理解的部分?例如，@ 符号表示人们希望在哪里找到索引?为什么是 #?

My question is: is this just something that I have to memorize, or can this syntax be broken down into understandable parts? For instance, what does the @ symbol mean where one would expect to find the index? Why the #?

推荐答案

# 在变量引用的开头表示获取变量值的长度.对于普通变量，这意味着它的长度(以字符为单位).# 是数字"符号，因此您可以将其记住为变量中事物的数量".

# at the beginning of a variable reference means to get the length of the variable's value. For a normal variable this means its length in characters. # is the "number" sign, so you can remember this as meaning "the number of things in the variable".

@ 或 * 在数组索引中表示使用整个数组，而不是特定元素，它返回的不是字符数，而是字符数数组元素.* 在许多上下文中用作通配符，因此这应该很容易记住.此外，$* 和 $@ 用于表示 shell 脚本的所有参数，因此与所有数组元素的并行应该是显而易见的.

@ or * in an array index means to use the whole array, not a specific element, and instead of returning the number of characters, it returns the number of array elements. * is used as a wildcard in many contexts, so this should be easy to remember. Also, $* and $@ are used to mean all the arguments to a shell script, so the parallel with all the array elements should be obvious.

你不能只写${#arrayname}，因为当你使用一个没有下标的数组变量时，它相当于数组的元素0.所以${#arrayname}和${#arrayname[0]}是一样的，都是数组第一个元素的字符数.

You can't just write ${#arrayname} because when you use an array variable without a subscript, it's equivalent to element 0 of the array. So ${#arrayname} is the same as ${#arrayname[0]}, which is the number of characters in the first element of the array.

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