Looks to me like your regexp is saying: 
... \s*([^,]+)\s*,...
Find some whitespace, or perhaps none at all.
Find anything that is not a comma, at least once, 
which *includes* whitespace, then...
Find some more whitespace, perhaps none
Find a comma

[download]

Since perl is greedy, it takes the whitespace into the parens, and leaves nothing for the \s* afterwards to match.

I came up with this: 

m#(?:[^,]*,\s*){3}(.*?)\s*,#

[download]
which seems to do the trick. Breaking it down: 
(?:        ## Group, but do not store it into $1
[^,]*      ## Anything that is not a comma
,          ## Followed by a comma
\s*        ## Followed by possible whitespace
){3}       ## Find three of these (the first three)
(.*?)      ## Match any character, but don't be so greedy about it
\s*        ## Possible whitespace
,          ## Stops at first comma, because we are not being greedy

[download]

There is probably a better way to write it, but I'm tired and this seems to work.

In reply to Re: Regexp glitch while parsing record in CSV by turnstep
in thread Regexp glitch while parsing record in CSV by greenhorn

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