@echo off & setlocal enabledelayedexpansion
set i=1
for /f %%a in (1.txt) do (
  if !i!==1 (set installPath=%%a) else if !i!==2 (set fileName=%%a) else set installDirectory=%%a
  set /a i+=1
)

(for /f %%a in ('findstr /n .* 2.xml') do (
  set line=%%a
  set line=!line:*:=!
  if "!line!"=="" (echo.) else (
  set changed=!line:^<installPath^>=!
  if "!line!" neq "!changed!" (echo ^<installpath^>%installPath%^</installpath^>) else (
    set changed=!line:^<fileName^>=!
    if "!line!" neq "!changed!" (echo ^<fileName^>%fileName%^</fileName^>) else (
      set changed=!line:^<installDirectory^>=!
      if "!line!" neq "!changed!" (echo ^<installDirectory^>%installDirectory%^</installDirectory^>) else (
        echo !line!
      )
    )
  ))
))>3.xml