[dos-prepend.bat]

  copy /b prepend+original newfile
  if errorlevel 1 goto abort
  copy /y newfile original
  if errorlevel 1 goto abort
  del newfile
  del prepend
abort: rem end

# vs.

[unix-prepend]
#!/bin/sh
  cat prepend original > newfile && (
    mv -f newfile original;
    rm -f prepend )