Batch file to delete every nth file matching the spec

ndel.bat

@echo off
::: ndel - Deletes every nth file matching the spec
::: syntax: ndel.bat FILESPEC [skipcount] [sortorder]
:::           FILESPEC  - Files to be searched through
:::           skipcount - number of files to skip (optional - default 3)
:::           sortorder - File order (see: DIR for options - default N (name))

:: With no arguments show the above usage text
if "%~1"=="" findstr "^:::" "%~f0"&GOTO:EOF
set find=%1
set evry=4
set ord=n
if "%~2" neq "" set /a evry=(%2+1)
if "%~3" neq "" set ord=%3

set count=0
for /f %%f IN ('dir %find% /b /o%%ord%%') do (
    call :test_file "%%f"
)
GOTO:eof

:test_file
set /a _r="%count% %% %evry%"
if not %_r%==0 del %1
set /a count+=1
GOTO:eof