Validating Input in Batch File XY######## - Letters and Numbers Combination - validation

Question

I've created a batch/cmd file which executes correctly, but I would like to add a "validation" layer to check for correct input.
The input should be in the format of LETTER-LETTER-######## (Eight Numbers)
I'm more of a Bash person myself so I'm a little lost.
Here is a basic version of what I am using.
echo Please Input like so XY########
set /P INPUT=Type input: %=%

Answer 1

Ok. Here we go...
There is no way to do what you want if you read the input via set /P command. In this case you may test the input afterwards and repeat it until be correct...
To check the input at same time it is being typed you need to read and test each character individually. There are several ways to do that. The simplest one is based on choice command:
#echo off
setlocal EnableDelayedExpansion
echo Please Input like so XY########
set /P "=Type input: " < NUL
set "INPUT="
rem Get two *UPPERCASE* letters
set "letter= ABCDEFGHIJKLMNOPQRSTUVWXYZ"
for /L %%i in (1,1,2) do (
choice /C %letter% /N > NUL
for %%l in ("!errorlevel!") do set "INPUT=!INPUT!!letter:~%%~l,1!"
set /P "=!INPUT:~-1!" < NUL
)
rem Get eight digits
set "digit= 0123456789"
for /L %%i in (1,1,8) do (
choice /C %digit% /N > NUL
for %%l in ("!errorlevel!") do set "INPUT=!INPUT!!digit:~%%~l,1!"
set /P "=!INPUT:~-1!" < NUL
)
echo/
echo INPUT = "%INPUT%"
In this code:
Any letter pressed is converted to uppercase. This behavior may be cancelled including both upcase and lowcase letters in letter variable and adding /CS switch to choice command.
The last character input can not be deleted.
The input is automatically completed after the last character is input. No final ENTER key is needed.
If you want not this behavior and need more precise control on the input characters, then you must use another method; for example, reading the keys via xcopy trick. The link posted by Squashman above is an ample example on how to do that...

Answer 2

Aacini's answer also forces valid user input vs validating retroactilvey, his answer is less code and more "readable" IMO. I will be using his answer, but I figured I'd share this method.
I asked to "retroactively" validate user input, but #Squashmans commented URL forces valid user input in the first place.
https://www.dostips.com/forum/viewtopic.php?t=5775
Here is the "sanitized code" that I ended up with.
#echo off
#cls
::::START -- Section Blocks User from Inputting Invalid Data::::
setlocal
set "thisFile=%~F0"
call :ReadFormattedLine INPUT="__########" /M "Enter Input in Form XY########: "
echo/
:ReadFormattedLine var="mask" [/M "message"] [/P] [/F /W /A]
if "%~2" equ "" echo ERROR: Missing parameters & exit /B 1
setlocal EnableDelayedExpansion
set "var=%~1"
set "mask=%~2"
shift & shift
set "message="
if /I "%1" equ "/M" set "message=%~2" & shift & shift
set "password="
if /I "%1" equ "/P" set "password=1" & shift
set "switch=%~1"
set quote="
set "digit= 0 1 2 3 4 5 6 7 8 9 "
set "letter= A B C D E F G H I J K L M N O P Q R S T U V W X Y Z "
set "alphaNum=%digit%%letter%"
set "fmt=#_+?#"
set "show=$/\()[]:;,.- %digit: =%%letter: =%"
for /F %%a in ('copy /Z "%thisFile%" NUL') do set "CR=%%a"
for /F %%a in ('echo prompt $H ^| cmd') do set "BS=%%a" & set "SP=.%%a "
< NUL (
set /P "=%message%"
for /F "eol=| delims=" %%a in ('cmd /U /C echo !mask!^| find /V ""') do (
if "!fmt:%%a=!" neq "%fmt%" (
set /P "=Û"
) else if "%%a" neq " " (
set /P "=%%a"
) else (
set /P "=!SP!"
)
)
set /P "=!SP!!CR!%message%"
)
set "input="
set /A i=0, key=0
goto checkFormat
:nextKey
set "key="
for /F "delims=" %%a in ('xcopy /W "%thisFile%" "%thisFile%" 2^>NUL') do if not defined key set "key=%%a"
if "!key:~-1!" neq "!CR!" goto endif
if /I "%switch%" equ "/A" goto nextKey
if /I "%switch%" neq "/F" goto check/W
:nextField
set "format=!mask:~%i%,1!"
if "%format%" equ "" goto endRead
if "!fmt:%format%=!" equ "%fmt%" goto checkFormat
set /P "=Û" < NUL
set "input=%input% "
set /A i+=1
goto nextField
:check/W
if /I "%switch%" neq "/W" goto checkEmpty
if %i% equ 0 goto endRead
if "%format%" equ "" goto endRead
goto nextKey
:checkEmpty
if %i% gtr 0 goto endRead
goto nextKey
:endif
set "key=!key:~-1!"
if "!key!" equ "!BS!" (
if %i% gtr 0 (
if "%format%" equ "" (
set /P "=!SP!!BS!!BS!Û!BS!" < NUL
) else (
set /P "=Û!BS!!BS!Û!BS!" < NUL
)
set "input=%input:~0,-1%"
set /A i-=1
if !i! equ 0 set key=0
)
goto checkFormat
)
if "%format%" equ "" goto nextKey
if "!key!" equ "=" goto nextKey
if "!key!" equ "!quote!" goto nextKey
if "%format%" equ "#" ( rem Any digit
if "!digit: %key% =!" equ "%digit%" goto nextKey
) else if "%format%" equ "_" ( rem Any letter
if "!letter: %key% =!" equ "%letter%" goto nextKey
) else if "%format%" equ "+" ( rem Any letter, convert it to uppercase
if "!letter: %key% =!" equ "%letter%" goto nextKey
for %%a in (%letter%) do if /I "!key!" equ "%%a" set "key=%%a"
) else (
rem Rest of formats are alphanumeric: ? #
if "!alphaNum: %key% =!" equ "%alphaNum%" goto nextKey
if "%format%" equ "#" ( rem Convert letters to uppercase
for %%a in (%letter%) do if /I "!key!" equ "%%a" set "key=%%a"
) else if "%format%" neq "?" echo ERROR: Invalid format in mask: "%format%" & exit /B 2
)
)
if defined password (
set /P "=*" < NUL
) else (
set /P "=%key%" < NUL
)
set "input=%input%%key%"
:nextFormat
set /A i+=1
:checkFormat
set "format=!mask:~%i%,1!"
if "%format%" equ "" (
if /I "%switch%" equ "/A" goto endRead
if /I "%switch%" equ "/M" goto endRead
goto nextKey
)
if "!show:%format%=!" neq "%show%" (
if "!key!" equ "!BS!" (
if "%format%" neq " " (
set /P "=%format%!BS!!BS!Û!BS!" < NUL
) else (
set /P "=!SP!!BS!!BS!Û!BS!" < NUL
)
set "input=%input:~0,-1%"
set /A i-=1
if !i! equ 0 set key=0
goto checkFormat
) else (
if "%format%" neq " " (
set /P "=%format%" < NUL
) else (
set /P "=!SP!" < NUL
)
set "input=%input%%format%"
goto nextFormat
)
)
if "%input:~-1%!key!" equ " !BS!" (
set /P "=Û!BS!!BS!" < NUL
set "input=%input:~0,-1%"
set /A i-=1
goto checkFormat
)
goto nextKey
:endRead
echo/
endlocal & set "%var%=%input%"
echo %INPUT%
pause
exit /B