makegitsha1.bat

@echo off
set "file=%~dp0git_sha1.h"
set "cmd=git rev-parse HEAD"
set "cmd2=git show -s --format^=%%ci HEAD"
set "cmd3=git rev-parse --short HEAD"

set "git_sha1_orig=#define GIT_SHA1"
set "git_sha1=#define GIT_SHA1"
set "git_date_orig=#define GIT_DATE"
set "git_date=#define GIT_DATE"
set "git_short1_orig=#define GIT_SHORT1"
set "git_short1=#define GIT_SHORT1"

for /f "delims=" %%i in ('^"%cmd%^"') do set "git_sha1=%git_sha1% "%%i""
for /f "delims=" %%i in ('^"%cmd2%^"') do set "git_date=%git_date% "%%i""
set git_date_temp=%git_date: =%
for /f "delims=" %%i in ('^"%cmd3%^"') do set "git_short1=%git_short1% "%%i""

(echo #ifndef git_sha1H
 echo #define git_sha1H
 if not "%git_sha1%"=="%git_sha1_orig%" echo %git_sha1%
 if "%git_sha1%"=="%git_sha1_orig%" echo %git_sha1% "Git Hash Unavailable"
 if not "%git_date_temp%"=="%git_date_orig%" echo %git_date%
 if "%git_date_temp%"=="%git_date_orig%" echo %git_date% "%date%_%time: =0%"
 if not "%git_short1%"=="%git_short1_orig%" echo %git_short1%
 if "%git_short1%"=="%git_short1_orig%" echo %git_short1% "Git Short Hash Unavailable"
 echo #define GERA "In memory of Georgi Piskunov, 03/06/2021"
 echo #endif)>"%file%"

rem echo #ifndef git_sha1H > %file%
rem echo #define git_sha1H >> %file%
rem if not "%git_sha1%"=="%git_sha1_orig%" echo %git_sha1% >> %file%
rem if "%git_sha1%"=="%git_sha1_orig%" echo %git_sha1% "Git Hash Unavailable" >> %file%
rem if not "%git_date_temp%"=="%git_date_orig%" echo %git_date% >> %file%
rem if "%git_date_temp%"=="%git_date_orig%" echo %git_date% "%date%_%time: =0%" >> %file%
rem echo #endif >> %file%

rem from https://stackoverflow.com/questions/3814926/git-commit-date

rem And per my usual pattern, I've immediately figured it out because I can't leave it alone and let people answer.

rem I also needed to escape the carat in the format: `set cmd2=git show -s --format=^^=%%ci HEAD` works as expected.