[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.
Yes, Its behavior is exactly as you expected.
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 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!