Which notation is most preferable, why?
How to act with variable names that do not have values: should names be left or deleted, should there be "Empty absent vars" switch?
To my mind $var_name preferred to %var_name% and $(var_name).

edit: revolution, is not this an avatar(incarnation) of a person into your sight :?

edemko: Are you asking about how fasm should work with environment variables when assembling, or for your own programs when running?

A signature is something you can choose to have on a post-by-post basis. An avatar would be something that you choose on a site-wide basis.

own
you might have heard my plans about a tool menu for fasmw
basic controls are:
-tool alias
-tool path
-tool working directory
-tool args
+edit button for every property and OK and SAVE buttos

an idea about vars is to extract file(being assembled) path/name/extension and propose them to user as variables
system variables must be recognized too
i would also wanted setting global-visible %FASMDIR% etc variable as %COMMANDER_PATH% e.g. from Total Commander so that another apps could access fasm-following tools
thus people asked

In that case:

There is not really a "preferable" notation. It will likely depend upon other aspects as to how it fits with the rest of the syntax used in other parts of your code.

Also, dealing with missing or empty variables will be situation dependant. No single way will be right for all cases. And empty or missing %PATH% is usually perfectly acceptable. But an empty or missing %library% might be fatal.

are you talking about TG's code planning and someone's insertions?

I'm talking about any code where EV expansion is used.

If it is for, say, perl then %var% doesn't fit well within the language syntax. But if it is for a batch file then %var% seems a good fit.

%% then?