[greg zakharov]

megaloman, Вы явно усложняете:

Код:

@echo off
  setlocal enabledelayedexpansion
    set "map=1583shn"
    set "i=0"
    :loop
      set /a "i+=1", "j=7*%random%/32767"
      set "r=!r!!map:~%j%,1!"
      if !i! neq 3 goto:loop
    echo:%r%
  endlocal
exit /b