Check in batch script if variable is defined

[hatheroldev]

This pull-request fixes issue #52.

[rejeep]

I don't run Windows and don't know the language, can you please explain why this solves the problem (and hopefully not break something else)?

[hatheroldev]

The old code tried to check, whether the variable inside_emacs is set. To do so it compared [] with the expansion [%inside_emacs%].

• If the variable is not set it expands to [] and we have the test expression not []==[] and the false block () is not executed.
• If the variable contains the something, e.g. foo, we get the test expression not [foo]==[] and the true block () is executed.

Now is seems that, compared to older emacs versions, the content of inside_emacs changed and now contains a comma. In my case this is 27.0.50,compile. That comma has some meaning to the parser. The test expression becomes not [27.0.50 followed by compile]==[], which does not make sense for the parser at this point.

Since we do not care about the actual content of inside_emacs we can use the test expression not defined inside_emacs, which explicitly tests for the variable being set. A bonus advantage is that this documents the intended test, compared to the former cryptic test.

You can read more about the syntax here or here.

[rejeep]

Thanks for the explanation. I added you as a collaborator, feel free to merge.