取消批处理脚本中 FOR /L 中的 SET

发布于 2025-01-08 05:50:36 字数 474 浏览 1 评论 0原文

p谁能解释一下为什么 SET 在下面的代码中没有做任何事情？

ECHO OFF
FOR /L %%b IN (-1,1,1) DO (
SET /A _lat=%%b
ECHO variable lat: %_lat%
ECHO variable b: %%b
ECHO:
)

：输出：

variable lat:
variable b: -1

variable lat:
variable b: 0

variable lat:
variable b: 1

我尝试了没有 /A 的 SET 当然，我在 FOR 中尝试了其中变量 %%b 是来自文件的字符串并且它正常工作，但就在这里当变量 %%b 是一个变化的数字时，它不起作用。

如果您有任何建议，请告诉我。当然，我可以只使用 %%b 来显示我想要的内容，但由于这是较大脚本的一部分，为了使其更具可读性，我想使用适当的变量。

原文

pCan anyone explain why SET is not doing anything in the following code?:

ECHO OFF
FOR /L %%b IN (-1,1,1) DO (
SET /A _lat=%%b
ECHO variable lat: %_lat%
ECHO variable b: %%b
ECHO:
)

output:

variable lat:
variable b: -1

variable lat:
variable b: 0

variable lat:
variable b: 1

I tried SET without /A of course, I tried that within FOR where variable %%b was a string from a file and it worked normally, but just here when variabl %%b is a changing number it does not work.

If you would have any suggestion, please tell me. Of couse I can use just %%b to diplay what I want, but since this is a part of larger scritp, to make it more readable, I would like to but the vaules to approproate variable.

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穿透光 2025-01-15 05:50:36

您需要使用ENABLEDELAYEDEXPANSION。尝试使用以下方法：

setlocal ENABLEDELAYEDEXPANSION

echo off
for /L %%b in (-1,1,1) do (
    set /A _lat=%%b
    echo variable lat: !_lat!
    echo variable b: %%b
    echo:
)

You need to use ENABLEDELAYEDEXPANSION. Try with the below:

setlocal ENABLEDELAYEDEXPANSION

echo off
for /L %%b in (-1,1,1) do (
    set /A _lat=%%b
    echo variable lat: !_lat!
    echo variable b: %%b
    echo:
)

回复收藏 0 原文

因为看清所以看轻 2025-01-15 05:50:36

查看控制台中 SET /? 的输出。您需要启用并使用延迟环境变量扩展才能使其正常工作。以下是帮助集中的相关片段：

最后，支持延迟环境变量扩展
额外。默认情况下，此支持始终处于禁用状态，但可能会
通过 /V 命令行开关切换到 CMD.EXE 启用/禁用。参见 CMD /？
延迟环境变量扩展对于解决问题很有用
当前扩展的局限性，当线路
文本是被读取的，而不是在执行时。下面的例子
演示了立即变量扩展的问题：
设置 VAR=之前
如果“%VAR%”==“之前”(
    设置VAR=之后
    if "%VAR%" == "after" @echo 如果你看到这个，它就起作用了
）
永远不会显示该消息，因为两个 IF 语句中都有 %VAR%
当读取第一个 IF 语句时被替换，因为它在逻辑上
包括 IF 的主体，它是一个复合语句。所以
复合语句中的 IF 实际上是在比较“before”与
“之后”永远不会相等。同样，下面的例子
将无法按预期工作：
<前><代码>设置列表=
对于 (*) 中的 %i，请设置 LIST=%LIST% %i
回显%列表%
因为它不会在当前目录中建立文件列表，
而是将 LIST 变量设置为最后找到的文件。
同样，这是因为 %LIST% 仅在以下情况下扩展一次：
读取FOR语句，此时LIST变量为空。
所以我们正在执行的实际 FOR 循环是：
对于 (*) 中的 %i 设置 LIST= %i
它只是不断将 LIST 设置为找到的最后一个文件。
延迟环境变量扩展允许您使用不同的
字符（感叹号）来扩展环境变量
执行时间。如果启用延迟变量扩展，则上述
示例可以编写如下以按预期工作：
设置 VAR=之前
如果“%VAR%”==“之前”(
    设置VAR=之后
    如果“！VAR！” ==“after”@echo 如果你看到这个，它就起作用了
）

设置列表=
对于 (*) 中的 %i，请设置 LIST=!LIST! ％我
回显%列表%

Take a look at the output of SET /? in a console. You need to enable and use delayed environment variable expansion for this to work. Here's the relevant snippet from the help set:

Finally, support for delayed environment variable expansion has been
added. This support is always disabled by default, but may be
enabled/disabled via the /V command line switch to CMD.EXE. See CMD /?
Delayed environment variable expansion is useful for getting around
the limitations of the current expansion which happens when a line
of text is read, not when it is executed. The following example
demonstrates the problem with immediate variable expansion:
set VAR=before
if "%VAR%" == "before" (
    set VAR=after
    if "%VAR%" == "after" @echo If you see this, it worked
)
would never display the message, since the %VAR% in BOTH IF statements
is substituted when the first IF statement is read, since it logically
includes the body of the IF, which is a compound statement. So the
IF inside the compound statement is really comparing "before" with
"after" which will never be equal. Similarly, the following example
will not work as expected:
set LIST=
for %i in (*) do set LIST=%LIST% %i
echo %LIST%
in that it will NOT build up a list of files in the current directory,
but instead will just set the LIST variable to the last file found.
Again, this is because the %LIST% is expanded just once when the
FOR statement is read, and at that time the LIST variable is empty.
So the actual FOR loop we are executing is:
for %i in (*) do set LIST= %i
which just keeps setting LIST to the last file found.
Delayed environment variable expansion allows you to use a different
character (the exclamation mark) to expand environment variables at
execution time. If delayed variable expansion is enabled, the above
examples could be written as follows to work as intended:
set VAR=before
if "%VAR%" == "before" (
    set VAR=after
    if "!VAR!" == "after" @echo If you see this, it worked
)

set LIST=
for %i in (*) do set LIST=!LIST! %i
echo %LIST%