Batch increment part of variable name - variables

Question

How can I increment part of a variable name?
EG. i want to increment
filename holds something like mmddyyyy-prev01-Database.mdb
and I'm trying to rename it to mmddyyyy-prev02-Database.mdb
With the code
Setlocal EnableDelayedExpansion
set /a nextFileName=!fileName:~0,13!!fileName:~13!+1
and I get the error
Missing operator.
I am using this to make a batch sub that will recursively rename the prevXX items so that the newest one is always prev01. I'm also doing regular setlocal in my method to keep the variables from getting mixed up between the deeper calls

Answer 1

I'm going the hard way:
#ECHO OFF &SETLOCAL disableDelayedExpansion
FOR /f "delims=" %%x IN ('DIR /b /a-d /o-n *-prev*-Database.mdb') DO (
FOR /f "tokens=1-3*delims=v-" %%a IN ("%%~x") DO (
FOR /f "tokens=*delims=0" %%e IN ("0%%c") DO (
FOR /f %%f IN ('SET /a %%e+1') DO (
IF %%f LEQ 9 (
ECHO REN "%%~x" "%%~a-%%~bv0%%~f-%%~d"
) ELSE (
ECHO REN "%%~x" "%%~a-%%~bv%%~f-%%~d"
)
)
)
)
)
Just remove the ECHOs to make it working.

Answer 2

SET /A won't allow you do this.
You'll have to break up into two lines, like this:
SET BaseFileName=!FileName:~0,13!
SET /A Counter=!FileName:~13!+1
Then, put the pieces back together:
SET NextFileName=%BaseFileName%%Counter%-Database.mdb
NOTE: This will not handle your leading 0...you'll have to write more code for that.

Answer 3

...
set filename=mmddyyyy-prev01-Database.mdb
call :nextname
ren %filename% %newname%
...
:nextname
set /a newname=1%filename:~13,2%+1
set newname=%filename:~0,13%%newname:~-2%%filename:~15%
goto :eof
Whether you'd use ren %filename% %newname% or ren !filename! !newname! is a matter of context. You've posted insufficient code to be certain. If, as I suspect, you are executing the ren in a loop, then you would need the !var! form and delayedexpansion (with which you appear familiar.) Within the subroutine :nextname, the %var% form should be used.
but remember that you need to rename your existing files in reverse-alphabetical order, so
mmddyyyy-prev03-Database.mdb becomes mmddyyyy-prev04-Database.mdb
mmddyyyy-prev02-Database.mdb becomes mmddyyyy-prev03-Database.mdb
mmddyyyy-prev01-Database.mdb becomes mmddyyyy-prev02-Database.mdb