为什么设置批处理脚本变量会延迟? [英] Why is setting a batch script variable delayed?

问题描述

如何解决延迟变量分配?

How do I solve delayed variable assignment?

(我正在编造术语延迟变量分配"，因为它看起来像是一个合理的描述性短语).

示例批处理脚本代码script.bat:

Example Batch Script Code script.bat:

@echo off
set mylocation=%CD%
echo mylocation %mylocation%
echo CD %CD%

实际输出

C:> script.bat
mylocation
CD C:\

C:>

我想要它做(或认为会做)

What I want it to do (or thought it would do)

C:> script.bat
mylocation C:\
CD C:\

C:>

编辑(更改):如果脚本结束后我在命令提示符中回显％mylocation％，则它具有一个值.

Edit (changed): If I echo %mylocation% in command prompt after the script ends it has a value.

C:>echo %mylocation%
C:\

C:>

这是原始代码，您可以观看YouTube视频 https://youtu.be/jQzEFD3yISA-在这里我尝试显示尽可能多的细节，以便所有内容都是准确的.

This is the original Code, and you can view the youtube video https://youtu.be/jQzEFD3yISA - where I try to show as much detail as possible so that, everything is exact.

@echo off

set natasha_command=%1

if %natasha_command% == start (
    set mylocation=%CD%
    echo mylocation %mylocation%
    echo CD %CD%
)

goto :eof

推荐答案

在块语句(a parenthesised series of statements)中，解析整个块并然后执行.块中的任何%var%都将在解析该块时被该变量的值取代-在执行该块之前-相同的情况适用于FOR ... DO (block).

Within a block statement (a parenthesised series of statements), the entire block is parsed and then executed. Any %var% within the block will be replaced by that variable's value at the time the block is parsed - before the block is executed - the same thing applies to a FOR ... DO (block).

因此，IF (something) else (somethingelse)将在遇到IF时使用%variables%的值执行.

Hence, IF (something) else (somethingelse) will be executed using the values of %variables% at the time the IF is encountered.

克服此问题的两种常见方法是:1)使用setlocal enabledelayedexpansion并使用!var!代替%var%来访问更改后的var值，或2)调用子例程以使用更改值.

Two common ways to overcome this are 1) to use setlocal enabledelayedexpansion and use !var! in place of %var% to access the changed value of var or 2) to call a subroutine to perform further processing using the changed values.

因此请注意使用CALL ECHO %%var%%来显示更改后的var值. CALL ECHO %%errorlevel%%显示，但遗憾的是会显示RESETS错误级别.

Note therefore the use of CALL ECHO %%var%% which displays the changed value of var. CALL ECHO %%errorlevel%% displays, but sadly then RESETS errorlevel.

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