[Yechezkel Mett]
,\s*(),
means find a ',' followed by any number of spaces followed by a ',' and capture an empty string.
Yes, now I see. Thank you, Yechezkel.
The others are similar.
r: "([^"]*)"|([^\s,"]+)|,\s*(),|^\s*(),|,\s*()$
empty,,,fields, , , like this [empty][][fields][][like][this] ,,, [][]
There are 2 empty tokens in between each 3 contiguous ',' but only one
for
each is detected.
Yes, that's a mistake. When matching ,, as an empty field the second ',' is eaten and can no longer be used as the beginning of the next field.
"([^"]*)"|([^\s,"]+)|,\s*()(?=,)|^\s*()(?=,)|,\s*()$
should work. (?=) is a lookahead, it checks that the pattern (',' in this case) matches at this point, but doesn't eat any input.
Likewise, for (2), I get:
r: "([^"]*)"|([^\s,"]+)|(?:^|,)\s*()(?:$|,)
empty,,,fields, , , like this [empty][fields][like][this]
This time, the behavior is no different than the 'original' version.
I get the same results as the first version. Perhaps it wasn't escaped
Yes, Its behavior is exactly as you expected. properly? Yes, you are right. My different result came from my incorrect escaping unintentionally. B/Rgds Max P.S I've found some 'complete' reference (books) on RE. However it's this thread of discussion that has indeed triggered a leap of my understanding of RE. And, I have also had a revisit, not so deep though, to SPIRIT.Qi, following the direction of Michael. (Qi is a power tool I believe I definitely will use, and its siblings.) Now I'm able to comprehend quite 'complex' expression, including whose appeared in this thread. Thank you Michael, Yechezkel, Stephan for your kind help!