|It gives me something to do when I have nothing else to do which is most of the time.|
You should try learning a real scripting/programming language. Something with a written rule set. If you have Vista or 7, you can use PowerShell. If you have any version after Win95 pre-IE, you can use VBScript. There are real programming languages, like C# or any of the .NET languages. You could go with something not focused exclusively on Windows, like Python.
Could you just type if /a %buy%==hatchet set hatchet + =1 and in the beginning have set hatchet=0?
You have the "/a" on the wrong command, but yes, you can make a counter.
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