Replace specific comma's in a string.

[Russell Haley <russ.haley@...>]

Since my match and capture understanding in Lua is somewhat weak I am
looking for opportunities to improve my understanding. There is a SO
question about parsing a file here:

https://unix.stackexchange.com/questions/422526/remove-comma-outside-quotes

The crux of the question is to leave the commas within a quoted items
and replace all the outer "separator" commas with tilde (~). So parse
this:

123,"ABC, DEV 23",345,534.202,NAME

and return this:

123~"ABC, DEV 23"~345~534.202~NAME.

I've put together a couple of pieces but can't find any way to make it
into an answer without resorting to loops.

s = '123,"ABC, DEV 23",345,534.202,NAME'

print(s:match('".*,.*"'))
"ABC, DEV 23"

print(s:gsub('".*(,).*"','~'))
123,~,345,534.202,NAME  1


>>From what i can tell, there is no way to add exclusions to patterns so
at this point I'm stumped. Instead of asking for the solution and
studying it, I'd like to first ask for a hint from the mailing list.
My questions are:

- Is it possible to do this in a single call to gsub (I'm hoping yes)?
If not, I will look first at one or two calls (i.e. match and then
gsub) and using a loop.
- Is this something that would be better done with LPEG?

I'll likely ask is people can share possible answers later to see if
my solution is at all reasonable.

Thanks

Russ