Swithces redirections in hosts file based on environment variable.

hosts.bat

SET InputFile=%SystemRoot%\System32\drivers\etc\hosts
SET OutputFile=%SystemRoot%\System32\drivers\etc\hoststemp

IF "%HOSTS_OVERRIDE%" == "" GOTO FIRST_RUN
IF "%HOSTS_OVERRIDE%"=="1" (
    SETX HOSTS_OVERRIDE 0
    GOTO TEST
) else (
    SETX HOSTS_OVERRIDE 1
    GOTO LIVE
)
:FIRST_RUN
SETX HOSTS_OVERRIDE 0
ECHO # LIVEDMZ>>%InputFile%
GOTO TEST

:TEST
SET "_strFind=# LIVEDMZ"
SET "_strInsert=10.249.103.7 apps.be.katoennatie.com"
GOTO REPLACE_HOST

:LIVE
SET "_strFind=10.249.103.7 apps.be.katoennatie.com"
SET "_strInsert=# LIVEDMZ"
GOTO REPLACE_HOST

:REPLACE_HOST
@ECHO OFF
SETLOCAL DISABLEDELAYEDEXPANSION
>"%OutputFile%" (
  FOR /f "usebackq delims=" %%A in ("%InputFile%") do (
    ECHO.%%A | FINDSTR /C:"%_strFind%" 1>nul
    IF errorlevel 1 (ECHO %%A) ELSE (ECHO %_strInsert%)
  )
)
XCOPY /Q /Y /R %OutputFile% %InputFile%
:END