Windows 批处理文件：如果其他
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Windows Batch Files: if else
提问by MxLDevs
I'm doing a simple batch file that requires one argument (you can provide more, but I ignore them).
我正在做一个需要一个参数的简单批处理文件（您可以提供更多参数，但我忽略它们）。
For testing, this is what I have so far.
为了测试，这就是我到目前为止所拥有的。
if not %1 == "" (
dir /s/b %1
) else (
echo no
)
Basically, I want to say if an argument is provided, recursively display all the files in the folder. Otherwise, say no.
基本上，我想说如果提供了一个参数，递归地显示文件夹中的所有文件。否则，说不。
It works when I provide an argument, but if I don't provide one it'll just tell me ( was unexpected at this time.
当我提供一个参数时它会起作用，但如果我不提供一个它就会告诉我( was unexpected at this time。
I mean, it works, but I wanted to at least display a user-friendly message explaining why it doesn't work. How should I change the code?
我的意思是，它有效，但我想至少显示一条用户友好的消息，解释为什么它不起作用。我应该如何更改代码？
回答by schnaader
if not %1 == "" (
must be
必须是
if not "%1" == "" (
If an argument isn't given, it's completely empty, not even ""(which represents an empty string in most programming languages). So we use the surrounding quotes to detect an empty argument.
如果没有给出参数，则它完全是空的，甚至不是""（在大多数编程语言中表示空字符串）。所以我们使用周围的引号来检测空参数。
回答by jwd
Surround your %1with something.
%1用东西包围你。
Eg:
例如：
if not "%1" == ""
Another one I've seen fairly often:
另一个我经常看到的：
if not {%1} == {}
And so on...
等等...
The problem, as you can likely guess, is that the %1is literally replaced with emptiness. It is not 'an empty string' it is actually a blank spot in your source file at that point.
正如您可能猜到的那样，问题%1是实际上被空虚所取代。它不是“空字符串”，此时它实际上是源文件中的空白点。
Then after the replacement, the interpreter tries to parse the ifstatement and gets confused.
然后在替换后，解释器尝试解析if语句并感到困惑。
回答by David angulo
You have to do the following:
您必须执行以下操作：
if "%1" == "" (
echo The variable is empty
) ELSE (
echo The variable contains %1
)
回答by Darin
Another related tip is to use "%~1" instead of "%1". Type "CALL /?" at the command line in Windows to get more details.
另一个相关提示是使用“%~1”而不是“%1”。输入“呼叫/？” 在 Windows 的命令行中获取更多详细信息。
回答by mivk
An alternative would be to set a variable, and check whether it is defined:
另一种方法是设置一个变量，并检查它是否已定义：
SET ARG=%1
IF DEFINED ARG (echo "It is defined: %1") ELSE (echo "%%1 is not defined")
Unfortunately, using %1directly with DEFINEDdoesn't work.
不幸的是，%1直接使用 withDEFINED不起作用。
回答by skchoe
you have to do like this...
你必须这样做...
if not "A%1" == "A"
如果不是“A%1”==“A”
if the input argument %1 is null, your code will have problem.
如果输入参数 %1 为空，你的代码就会有问题。
