달력

@echo off

set SELF=%~n0
set HELP=Usage: %SELF% MONTH YEAR

setlocal enabledelayedexpansion
  :: 値が数値か確認
  (echo %~1) | findstr /r "[^0-9]." > NUL && (
    >&2 echo %HELP%
    exit /b 1
  )
  (echo %~2) | findstr /r "[^0-9]." > NUL && (
    >&2 echo %HELP%
    exit /b 1
  )

  :: 位置パラメーターを取得
  set y=%~2
  set m=%~1

  :: 値が範囲内か確認
  if %m% lss  1 (
    >&2 echo %SELF%: illegal month value: use 1-12
    exit /b 1
  )
  if %m% gtr 12 (
    >&2 echo %SELF%: illegal month value: use 1-12
    exit /b 1
  )
  if %y% lss    1 (
    >&2 echo %SELF%: illegal year value: use 1-9999
    exit /b 1
  )
  if %y% gtr 9999 (
    >&2 echo %SELF%: illegal year value: use 1-9999
    exit /b 1
  )

  :: 指定された日の曜日を取得（月初の曜日）
  call :get_day_of_week %y% %m% 1
  set w=%ERRORLEVEL%

  :: 指定された月の日数を取得
  set i=1
  for %%i in (31 28 31 30 31 30 31 31 30 31 30 31) do (
    set d[!i!]=%%i
    set /a i+=1
  )
  set d=!d[%m%]!

  :: うるう年を考慮
  if %m% equ 2 (call :is_leap_year %y% || set /a d+=1)

  :: カレンダーを表示
  if %m% lss 10 (
    echo %y%/ %m%
  ) else (
    echo %y%/%m%
  )
  echo Su Mo Tu We Th Fr Sa
  set t=
  for /l %%i in (1,1,%w%) do (set t=!t!   )
  for /l %%d in (1,1,%d%) do (
    if %%d lss 10 (set t=!t! )
    set t=!t!%%d
    call :get_day_of_week %y% %m% %%d
    set n=!ERRORLEVEL!
    if !n! equ 6 (echo !t! & set t=) else (set t=!t! )
  )
  if not "%t%" == "" echo %t%
  echo.

  exit /b 0
endlocal
goto :EOF

:is_leap_year
setlocal
  set n=0

  set /a n=%1%%400
  if %n% equ 0 exit /b 1

  set /a n=%1%%100
  if %n% equ 0 exit /b 0

  set /a n=%1%%4
  if %n% equ 0 exit /b 1

  exit /b 0
endlocal
goto :EOF

:get_day_of_week
setlocal
  set y=%1
  set m=%2

  if %m% leq 2 (
    set /a y-=1
    set /a m+=12
  )

  :: ツェラーの公式
  set /a w=(5*%y%/4-%y%/100+%y%/400+(26*%m%+16)/10+%3)%%7
endlocal & exit /b %w%
goto :EOF