How to verify if variable contains valid filename in Windows Batch - validation

Question

I'm asking user to provide filename in Windows Batch, by using this command:
set /p my_filename=Enter filename for this project
How can I verify that %my_filename% contains valid Windows filename (not path) and re ask user if it does not?
EDIT
The file in question does not yet exists when running the script (it will be created by script)

Answer 1

#echo off
setlocal enableextensions disabledelayedexpansion
:askFile
rem Retrieve filename. On empty input ask again
set /p "my_file=Enter filename for this project: " || goto :askFile
rem Use delayed expansion to avoid problems with special characters
setlocal enabledelayedexpansion
rem Disable delimiters and end of line characters in for command
for /f delims^=^ eol^= %%a in ("!my_file!") do (
rem Cancel delayed expansion to avoid ! removal during expansion
endlocal
rem Until checked, we don't have a valid file
set "my_file="
rem Check we don't have a path, it is not a folder and the file exists
if /i "%%~a"=="%%~nxa" if not exist "%%~a\" if exist "%%~a" set "my_file=%%~nxa"
)
rem If we don't have a file name (it was not valid) ask again
if not defined my_file goto :askFile
echo Selected file is "%my_file%"
edited to adapt to comments
#echo off
setlocal enableextensions disabledelayedexpansion
:askFile
rem Retrieve filename. On empty input ask again
set /p "my_file=Enter filename for this project: " || goto :askFile
rem See Naming Files, Paths, and Namespaces
rem https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247%28v=vs.85%29.aspx
rem NOTE: From here, we will be enabling/disabling delayed expansion
rem to avoid problems with special characters
setlocal enabledelayedexpansion
rem Ensure we do not have restricted characters in file name trying to use them as
rem delimiters and requesting the second token in the line
for /f tokens^=2^ delims^=^<^>^:^"^/^\^|^?^*^ eol^= %%y in ("[!my_file!]") do (
rem If we are here there is a second token, so, there is a special character
echo Error : Non allowed characters in file name
endlocal & goto :askFile
)
rem Check MAX_PATH (260) limitation
set "my_temp_file=!cd!\!my_file!" & if not "!my_temp_file:~260!"=="" (
echo Error : file name too long
endlocal & goto :askFile
)
rem Check path inclusion, file name correction
for /f delims^=^ eol^= %%a in ("!my_file!") do (
rem Cancel delayed expansion to avoid ! removal during expansion
endlocal
rem Until checked, we don't have a valid file
set "my_file="
rem Check we don't have a path
if /i not "%%~a"=="%%~nxa" (
echo Error : Paths are not allowed
goto :askFile
)
rem Check it is not a folder
if exist "%%~nxa\" (
echo Error : Folder with same name present
goto :askFile
)
rem ASCII 0-31 check. Check file name can be created
2>nul ( >>"%%~nxa" type nul ) || (
echo Error : File name is not valid for this file system
goto :askFile
)
rem Ensure it was not a special file name by trying to delete the newly created file
2>nul ( del /q /f /a "%%~nxa" ) || (
echo Error : Reserved file name used
goto :askFile
)
rem Everything was OK - We have a file name
set "my_file=%%~nxa"
)
echo Selected file is "%my_file%"
goto :eof

Answer 2

You could strip posible path with a for
Check with findstr Regular Expression for only allowed chars
Another findstr to exclude possible device names
:: Q:\Test\2017\08\20\SO_45780452.cmd
#Echo off
:loop
set "my_filename="
set /p "my_filename=Enter filename for this project: "
set "test="
for %%A in ("%my_filename%") Do Set "test=%%~nxA"
If "%test%" neq "%my_filename%" (
Echo no drive/path please
Goto :loop
)
echo:%my_filename%|findstr /i "^[0-9A-Z.-_]*$" >Nul 2>&1 ||(
Echo invalid chars
goto :loop
)
:: check possible device name and reject
echo:%my_filename%|findstr /i "^aux$ ^con$ ^com[0-9]*$ ^lpt[0-9]*$ ^nul$ ^prn$" >Nul 2>&1 && (
Echo invalid device name
goto :loop
)
:: my_filename should be a tolerable name

Answer 3

Very elementary filename validity control:
echo %my_filename%| findstr /R /C:"*\.*"
There could be glitches with reserved DOS-times names (CON, PRN, NUL, etc..) and/or some special characters, so maybe you could simply try to store something into file under provided name, and than check if file was created successfully. Something like:
:getfilename
set /p my_filename=Enter filename for this project
echo A>%my_filename%
if not exist %my_filename% (echo Wrong filename & goto getfilename) else (del %my_filename% >NUL)
ALL UNTESTED!! Check if working directory is empty first.