Re: [NSE] Locals, Globals, and You (ALL script writers please read)

[Patrick Donnelly <batrick () batbytes com>]

On Sat, Aug 14, 2010 at 11:32 PM, Ron <ron () skullsecurity net> wrote:
> One thing I run into is situations where I use the same variable (like status) multiple times, but use a different 
> variable alongside. For example:
> status, variable1 = function1()
> status, variable2 = function2()
> status, variable3 = function3()
>
> There doesn't seem to be a clean way to do that, unless it's okay to re-declare status as local:
> local status, variable1 = function1()
> local status, variable2 = function2()
> ...

This *is* ok. There's nothing wrong with it except each new
declaration of status (when declared in the same block) will use up a
new register. This will almost certainly not cause problems unless you
use the maximum number of registers (~250). I would say go ahead and
do it.

> That's when I start declaring stuff at the top of the function. It gets even worse when I need to use the return 
> value of 'status' in a call to the next function, because then you're re-declaring it and using it on the same line 
> and that's all kinds of not good.

Like I said above, it's ok to do. It's neither good nor bad.

> I know you have a script that'll find accidental global accesses. And that's good, because I've spent a lot of time 
> tracking down nasty bugs that are caused by exactly that (accidental globals). But is there any way to make it easier 
> to run your script? Like, even if it can't be automated (nmap --script-check-globals?), at least including it in Nmap 
> or something? I wish Lua wouldn't even let you declare a global within a function. I like Ruby's style better, of 
> using @@blah for a global, to totally differentiate it.

It's a useful script but I'd prefer to fix the habits that help cause
the problems.

> On a related note, I'm pretty sure there's currently no "style guide" for writing scripts, and I'm sure that if you 
> took the 5 people who write the most scripts, none of them would agree on proper styles (even things like whitespace, 
> comments, variable declarations, etc). But maybe we should start looking into building a style guide.

This is a good idea.

-- 
- Patrick Donnelly
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