只读是什么意思或做什么？

Question

在这种情况下 readonly 意味着什么或做什么？我从未见过或听说过它。

a="testString"; b=a; readonly b; b=25;

另外，最后b的最终值会是25吗？

Answer 1

它使变量只读。从help readonly：

readonly: readonly [-aAf] [name[=value] ...] or readonly -p
    Mark shell variables as unchangeable.

    Mark each NAME as read-only; the values of these NAMEs may not be
    changed by subsequent assignment.  If VALUE is supplied, assign VALUE
    before marking as read-only.

    Options:
      -a    refer to indexed array variables
      -A    refer to associative array variables
      -f    refer to shell functions
      -p    display a list of all readonly variables and functions

    An argument of `--' disables further option processing.

    Exit Status:
    Returns success unless an invalid option is given or NAME is invalid.

$b当以只读方式创建 b 时，将始终返回“1”。举个例子：

$ a=1
$ a=2
$ readonly b=1
$ b=2
bash: b: readonly variable
$ echo "$a"
2
$ echo "$b"
1