Windows Forms

FOR /F "delims=" %%I IN ('DIR . /B /O:-D /T:C') DO COPY "%%I" .\new.txt & GOTO :END
:END
START /MAX new.txt

@echo off
REM generate next PO NNN.2011.txt where NNN is a number

SET FILENAME=PO 156.2011.txt
REM SET FILENAME=PO ABC.2011.txt
ECHO Initial filename %FILENAME%

REM get 2nd token using '.' and ' ' delimiters
for /F "tokens=2 delims=. " %%a in ("%FILENAME%") do SET /a NNN=%%a

REM what did we get
ECHO NNN %NNN%

REM Increment the value
SET /a NNN=%NNN% + 1
ECHO NNN+1 = %NNN%

SET FILENAME=PO %NNN%.2011.txt
ECHO New filename %FILENAME%
PAUSE

@echo off
REM generate next PO NNN.2011.txt where NNN is a number

SET FILENAME=PO 156.2011.txt
REM SET FILENAME=PO ABC.2011.txt
ECHO Initial filename %FILENAME%

REM get 2nd token using '.' and ' ' delimiters
REM Store token as both number and text
for /F "tokens=2 delims=. " %%a in ("%FILENAME%") do SET /a NNN=%%a & SET TEXT=%%a

REM what did we get
ECHO NNN %NNN%  TEXT %TEXT%

REM Should be the same if the token is a decimal number
IF %NNN%==%TEXT% (
  ECHO Yippee, got a number
  
  REM Increment the value
  SET /a NNN=%NNN% + 1

  ECHO NNN+1 = %NNN%
  SET FILENAME=PO %NNN%.2011.txt

  ECHO New filename %FILENAME%
) ELSE (
  ECHO Darn it, got a non numeric token
)

PAUSE