The pre-commit hook script written as Batch file in windows OS.
Search for pre-commit.bat file in visual SVN installed directory.
We need to configure the bat file as per our requirement.
Please find the blow in pre-commit.bat file
REM Concatenate all the lines in the commit message
FOR /F "usebackq delims==" %%g IN (`%SVNLOOK% log -t %TXN% %REPOS%`) DO SET M=!M!%%g
REM Make sure M is defined
REM Here the <EXPECTED CHAR> is the length we require
IF NOT "%M:~<EXPECTED CHAR>,1%"=="" goto NORMAL_EXIT
echo "COMMENT ON COMMIT MUST BE AT LEAST <EXPECTED CHAR> LETTERS" >&2
Hope this will help you to resolve your problem