neorobin

@echo off & setlocal enabledelayedexpansion
set "y=%date:~0,4%" & set "m=%date:~5,2%" & set /a "m=1!m!-101, m=m+(^!m)*12"
set /a "f=^!(m-2), s=^!(m-4)|^!(m-6)|^!(m-9)|^!(m-11)" & rem 上月是否2月或小月
set /a "leap=^!(y%%4) & ^!^!(y%%100) | ^!(y%%400)" & rem 今年是否闰年
set /a "d=f*(28+leap)+s*30+(^!f&^!s)*31" & rem 上月有 !d! 天
set /a "y1=y-^!(m-12)"
set "m=0!m!" & set "m=!m:~-2!" & set "d=0!d!" & set "d=!d:~-2!"
echo 上个月月末的日期是 !y1!-!m!-!d!
pause
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