有效的批处理文件变量名称? [英] Valid batch file variable names?

问题描述

批处理文件存在以下问题.我简化了下面的问题.

I have the following problem with batch files. I simplify the problem below.

运行以下批处理文件foo.bat，以标准输出(在本例中为命令提示符窗口)而不是hey的形式返回word.

Running the following batch file, foo.bat, returns word in standard out (in this case, command prompt window) instead of hey.

@SET 1word="hey"
@ECHO %1word%

但是，从命令行执行echo %1word%会返回hey.

However, executing echo %1word% from the command line returns hey.

是否有理由/应该是这种情况?不允许数字作为环境变量名称的前缀吗?

Is there a reason this should/might be the case? Are numbers not allowed to prefix environment variable names?

推荐答案

您可以创建和使用名称以数字开头的环境变量 ，但这不是一个好主意，应避免使用 .定义变量没有问题.但是使用正常的百分比扩展进行扩展是个问题.

You can create and use environment variables with names that begin with a digit, but it is not a good idea, and should be avoided. Defining the variable is no problem. But expansion using normal percent expansion is a problem.

问题是批处理解析器在%1word%中看到了首字母%1，并扩展了第一个参数而不是变量.即使未传递任何参数，它仍会将不存在的第一个参数扩展为空字符串.在 https://stackoverflow.com/a/4095133/1012053 和https://stackoverflow.com/a/7970912/1012053 .

The problem is the batch parser sees the inital %1 in %1word% and expands the first argument instead of the variable. Even if no argument was passed, it still expands the non-existent first argument into an empty string. The rules are explained at https://stackoverflow.com/a/4095133/1012053 and https://stackoverflow.com/a/7970912/1012053.

您可以使用延迟扩展来访问变量.

You can access the variable using delayed expansion instead.

这是一个演示问题的示例脚本:

Here is an example script that demonstrates the issues:

@echo off
setlocal enableDelayedExpansion
set "1var=Environment variable value."
call :test "Argument 1 value"
exit /b

:test
echo arg 1 = %1
echo 1var normal = %1var%
echo 1var delayed = !1var!

-样本输出-

arg 1 = "Argument 1 value"
1var normal = "Argument 1 value"var
1var delayed = Environment variable value.

请注意，形式为%1的参数扩展仅是批处理脚本中的一个问题-与在命令提示符(非批处理)上下文中发出的命令无关.因此，您可以在命令提示符下定义1个单词，然后echo %1word%在命令提示符下可以正常工作.

Note that argument expansion of the form %1 is only an issue within a batch script - it is not relevant to commands issued in a command prompt (non batch) context. So you could define 1word from the command prompt and then echo %1word% would work fine from the command prompt.

由于复杂性，故事的寓意是-不要使用以数字开头的变量名".

Because of the complexities, the moral of the story is - "don't use variable names that begin with a digit".

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