Question

这是我的剧本：

@echo off
setlocal

for /f %%i in ('echo aaa/') do set REPO=%%i
if "%REPO%"=="" (
  echo No input
) else (
  echo %REPO:~-1%
  echo %REPO:~0,-1%
  if %REPO:~-1%==/ set REPO=%REPO:~0,-1%
  echo %REPO%
)

endlocal

请观察：

c:\dev\shunra\GlobalLibrary\Server>c:\Utils\hgbackup.cmd
/
aaa
aaa/

c:\dev\shunra\GlobalLibrary\Server>

发生了什么事？

修改

注意，我正在为REPO指定一个评估为“aaa”的东西，因此我希望它打印“aaa”，而不是“aaa /”。它让我发疯。

EDIT2

显然，这是罪魁祸首（来自set命令的帮助）：

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%

但我尝试使用!符号，但它对我不起作用。我使用屏幕上打印的get !或错误的结果。

Answer 1

正如评论和编辑过的问题所讨论的那样，您需要延迟扩展。

必须先启用延迟扩展才能使用它。在批处理脚本中，您可以使用setlocal enableDelayedExpansion

@echo off
setlocal enableDelayedExpansion

for /f %%i in ('echo aaa/') do set REPO=%%i
if "%REPO%"=="" (
  echo No input
) else (
  echo %REPO:~-1%
  echo %REPO:~0,-1%
  if %REPO:~-1%==/ set REPO=%REPO:~0,-1%
  echo !REPO!
)

endlocal

修改

如果更改IN（）子句以使REPO未定义，则上述操作失败。例如：in (echo.)

它失败了，因为整个IF / ELSE结构必须具有有效的语法，即使它不会执行ELSE子句。

如果未定义REPO，则

if %REPO:~-1%==/ set REPO=%REPO:~0,-1%

扩展为

if ~-1REPO:~0,-1

这是无效的语法。

使用延迟扩展可以解决问题。

@echo off setlocal enableDelayedExpansion for /f %%i in ('echo.') do set REPO=%%i if "%REPO%"=="" ( echo No input ) else ( echo %REPO:~-1% echo %REPO:~0,-1% if !REPO:~-1!==/ set REPO=%REPO:~0,-1% echo !REPO! ) endlocal

Answer 2

请注意，我正在为REPO分配评估为“aaa”
的内容

实际上，你有条件地分配一些东西。您是否测试过then-part是否实际执行（例如，echo If Entered）。

Answer 3

这对我有用（只是我整个剧本的摘录）

choice /C 1234567H /M "Select an option or ctrl+C to cancel"
set _dpi=%ERRORLEVEL%

if "%_dpi%" == "8" call :helpme && goto menu 

for /F "tokens=%_dpi%,*" %%1 in ("032 060 064 096 0C8 0FA 12C") do set _dpi=%%1
echo _dpi:%_dpi%:

如何在DOS批处理脚本中生存“延迟变量扩展”

3 个答案: