China DOS Union

For example, how do I check whether the value entered by the user is a valid expression?
For an IP address, how do I check whether it is less than 255?

You can set up a pattern like 192.168.0.XX, where XX represents a variable. You can define this when writing the batch file, and then use the IF statement to check it.
EQU - equal to
NEQ - not equal to
LSS - less than
LEQ - less than or equal to
GTR - greater than
GEQ - greater than or equal to
Use these values to check the range of your number. The error-handling ability of batch files isn't very strong to begin with, so it depends on how you write it and how well you can make the error handling.................

Better to give an example

@echo off
:start
set /p oo=Enter your numeric:
if %oo% LSS 0 goto ooo
if %oo% GEQ 255 goto ooo
goto ii
oo
echo Sorry! The number you entered is incorrect!!!
goto :start
:ii
echo The IP address you set is :192.168.0.%oo%

Hehe, quite interesting. Thanks.