Changing a batch file when its running

Question

I am running a long running batch file. I now realize that I have to add some more commands at the end of the batch file (no changes to exisiting content, just some extra co

Answer 1

Nearly like rein said, cmd.exe remember the file position (not only the line position) it's currently is, and also for each call it push the file position on an invisble stack.

That means, you can edit your file while it's running behind and before the actual file position, you only need to know what you do ...

A small sample of an self modifying batch
It changes the line set value=1000 continuously

@echo off
setlocal DisableDelayedExpansion
:loop
REM **** the next line will be changed
set value=1000
rem ***
echo ----------------------
echo The current value=%value%
 nul
echo(
(
call :changeBatch
rem This should be here and it should be long
)
rem ** It is neccessary, that this is also here!
goto :loop
rem ...
:changeBatch
set /a n=0
set /a newValue=value+1
set /a toggle=value %% 2
set "theNewLine=set value=%newValue%"
if %toggle%==0 (
   set "theNewLine=%theNewLine% & rem This adds 50 byte to the filesize.........."
)
del "%~f0.tmp" 2> nul
for /F "usebackq delims=" %%a in ("%~f0") DO (
   set /a n+=1
   set "line=%%a"
   setlocal EnableDelayedExpansion
   if !n!==5 (
       (echo !theNewLine!)
   ) ELSE (
       (echo !line!)
   )
   endlocal
) >> "%~f0.tmp"
(
  rem the copy should be done in a parenthesis block
  copy "%~f0.tmp" "%~f0" > nul
  if Armageddon==TheEndOfDays (
   echo This can't never be true, or is it?
  )
)
echo The first line after the replace action....
echo The second line comes always after the first line?
echo The current filesize is now %~z0
goto :eof