I hope you don't take this in a bad way, but I think you wouldn't get much comments if the goal of this problem is to simply parse the Apache log.

Let me put it this way: a "well formed" log file is really uninteresting to parse, since you don't expect bad entries in it. You know that the format for every line ( sans comment lines, if there are any ) are going to be in an identical format. Having that as a given, you don't really need to dig deep into the RE to come up with something that matches the lines.

Why not make the problem: "Let's come up with an RE that matches anything conforming to the Apache log from any given text file". And each field must look like a valid entry for a log: for example, for IP addresses, you can't match just any string just because it comes in the beginning of the line and it's a non-white space character. It must look like an IP address.

I think then you'll find people that may be interested in coming up with a new, improved RE.

Here's something I came up with from the top of my head:

DISCLAIMER: following code has NOT been tested, I don't even claim to know the apache log or the HTTP rfc all that well... bottom line, it's probably not a correct RE. Just an example

# IP address ( sort of ) -- too lazy to come up with 
# a more elaborate RE.... I'm sure somebody knows of
# a *real* RE for this :-)
# assuming it's never empty
(?:\d?\d?\d\.\d?\d?\d\.\d?\d?\d\.\d?\d?\d)

# HTTP code
# assuming it's never empty
\d\d\d

# bytes ( "-" if none )
(?:\d+|-)

# date. assuming it's never empty
[
   (?:[12][0-9]|3[01]|[1-9]) # date 10-19,20-29,30,31,1-9
     /
   (?:J(?:un|ul|an)|Feb|Ma(?:r|y)|A(?:pr|ug)|Sep|Oct|Nov|Dev) # month 
     /
   \d\d\d\d # year
     :
   (?:[01][0-9]|2[0-3]):(?:[0-5][0-9]):(?:[0-5][0-9]) # time
]
# HTTP Request -- don't know what the RFC says about this,
# so will stick with a simple one.
# assuming it's never empty
"[^"]+"

# Referrer
"(?:[^"]+|-)"

# I don't know what the second and third field does.
(?:\S+|-)
[download]

So putting that together...

   m/
      ^  # beginning of line
      (?:\d?\d?\d\.\d?\d?\d\.\d?\d?\d\.\d?\d?\d) # pseudo IP address
        [ ] # delimiter
      (?:\S+|-)[ ](?:\S+|-) # second and third fields...
        [ ] # delimiter
      \[
         (?:[12][0-9]|3[01]|[1-9]) # date 10-19,20-29,30,31,1-9
            /
         (?:J(?:un|ul|an)|Feb|Ma(?:r|y)|A(?:pr|ug)|Sep|Oct|Nov|Dev) # 
+month 
            /
         \d\d\d\d # year
            :
         (?:[01][0-9]|2[0-3]):(?:[0-5][0-9]):(?:[0-5][0-9]) # time
      \]
         [ ] # delimiter
      \d\d\d # HTTP code
         [ ] # delimiter
      (?:\d+|-) # bytes
         [ ] # delimiter
      "[^"]+" # HTTP request
         [ ] # delimiter
      "(?:[^"]+|-)" # referer
      $ # end
   /x;
[download]

As I said, just a thought. I'm sure there are bunch of things wrong with this RE. Feel free to point out any problems....

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