从批处理脚本中的变量中减去数字

Question

我是批处理脚本的新手，所以请对这个问题保持宽容。当我从'TodayDay'变量中减去1时，该值不会更新。以下是该行。

set /a "TodayDay=%TodayDay%-1"

我的用例是找到今天的日期是否小于'lastOpenedDate'变量，我想将'lastOpenedDate'设置为昨天的

set lastOpenedDate=2017-12-22
IF %TodayYear%-%TodayMonth%-%TodayDay% LSS %lastOpenedDate% (   
  echo Before Subtraction TodayDay is %TodayDay%
  set /a "TodayDay=%TodayDay%-1"
  echo After Subtraction TodayDay is %TodayDay%
)

当我运行上面的代码时，输​​出是：

Before Subtraction TodayDay is 20
After Subtraction TodayDay is 20

我从下面提到的代码中获得了其他变量值

for /F "skip=1 delims=" %%F in ('
    wmic PATH Win32_LocalTime GET Day^,Month^,Year /FORMAT:TABLE
') do (
    for /F "tokens=1-3" %%L in ("%%F") do (
        set TodayDay=0%%L
        set TodayMonth=0%%M
        set TodayYear=%%N
    )
)
set TodayDay=%TodayDay:~-2%
set TodayMonth=%TodayMonth:~-2%

我究竟做错了什么？

Answer 1

您需要使用delayed expansion的顶部栏搜索SO。这是＃1 FAQ。

更改

  set /a "TodayDay=%TodayDay%-1"
  echo After Subtraction TodayDay is %TodayDay%
)

至

  set /a "TodayDay=%TodayDay%-1"
)
echo After Subtraction TodayDay is %TodayDay%

一旦你熟悉delayed expansion.，这将是有意义的

现在你遇到的下一个问题（直到本月8日或9日才出现）是批量领先的0意味着“八进制”所以 - 你真的需要

  set /a "TodayDay=1%TodayDay%-1"
)
set "TodayDay=%TodayDay:~-2"
echo After Subtraction TodayDay is %TodayDay%

通过在日期编号前面加上1来增加100天数，然后你需要得到最后2个字符。