Windows batch: Get the next free numbered file name

getnumbered.cmd

@echo off
REM Initialize the first/lowest number
set NUMBER=0

REM Jump point: return here if the current file exists
:LOOP
REM Leave the loop in case the file doesn't exist
if not exist backup-%NUMBER%.zip goto DONE
REM Increment the counter
set /a NUMBER+=1
REM Well, loop...
goto LOOP

REM Jump point: we're done
:DONE

REM Now do something with the "next free numbered file"
move backup.zipe backup-%NUMBER%.zip