Check for null variable in Windows batch

To test for the existence of a command line paramater, use empty brackets:

IF [%1]==[] echo Value Missing

or

IF [%1] EQU [] echo Value Missing

The SS64 page on IF will help you here. Under “Does %1 exist?”.

You can’t set a positional parameter, so what you should do is do something like

SET MYVAR=%1

You can then re-set MYVAR based on its contents.