检查变量是否有值时执行批处理文件中断 [英] Executing batch file breaks when checking if variable has value

问题描述

要检查是否加载了文件，我使用以下命令加载其内容:

To chcek if file is loaded or not, I load its contents using:

set /p filevar=file.txt

并检查var是否为空:

and check if var is empty:

if "%filevar%"="" exit

当脚本chceks文件有多行时，脚本的执行停止，因此我认为chcecking失败.为什么脚本失败?如何正确执行这种检查?

When script chceks file with multiple lines, execution of script stops, so i suppose that chcecking fails. Why script fails? How to perform such check properely?

推荐答案

首先，您弄错了set /p命令的语法.照原样，它将以文本"file.txt"提示用户.我想你的意思是

Firstly, you've got the syntax of your set /p command messed up. As it is, it will prompt the user with the text "file.txt". I think what you mean is

set /p "filevar=" <file.txt

如果从命令行运行脚本，还应该将/b开关与exit一起使用，以防止关闭控制台窗口.

You should also use the /b switch with exit to prevent the console window from closing if your script is run from the command line.

但是，正如jeb所说，要检查left是否等于right，请使用==或equ.或者，正如dbenham提醒我的那样，如果您要检查一个空值，也可以使用if not defined.

But yeah, as jeb states, to check whether left equals right, either use == or equ. Or, as dbenham reminds me, if you're checking for an empty value, you can also use if not defined.

if "%filevar%"=="" exit /b
if "%filevar%" equ "" exit /b
if not defined filevar exit /b

所有三个语句将具有相同的结果 ¹ .

All three statements will have the same result¹.

在控制台窗口中，输入help if以获得更多信息.

In a console window, enter help if for more information.

¹ 值得一提的是，尽管这三个if语句在括号代码块之外具有相同的结果，但是只有第三个语句在括号内可以可靠地工作(例如在循环).如果在与%filevar%设置相同的代码块中使用前两个，则需要延迟扩展才能正常工作.

¹ It's worth mentioning that, while those three if statements have the same result outside of a parenthetical code block, only the third one will work reliably within parentheses (such as in a for loop). The first two would need delayed expansion to work properly if used within the same code block as %filevar% is set.

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