From: Brian Candler <b.candler@...>
Date: 2009-06-26T22:44:04+09:00
Subject: Re: regex that works on rubular.com but not in my program

Brian Candler wrote:
> Don't test them in rubular. Test them in irb or in ruby.

In a ruby file, you can comment out bits of them until you make it work, 
e.g.

re = %r{
(?#start: fetch the ip adress after IP)
IP\s((?:\d+\.){3}\d{1,3})
(?#end: fetch ip)
}x

#(?#start: flag).*:\s([PSF])(?#end:flag)
#(?#nothing more interesting on this line)
#.*
#
#(?#start: look for index pattern)
#^E.{5}@.{9}Q.{30,}
#(?#end: index)
#
#(?#start: get the username which is surrounded by multiple dots, 
minimum
#of 2 in the begining and 0+ after)
#\.{2,}(\w+)
#(?#end: username)
#}x

src = "12:23:59.378678 IP 85.225.108.54.54707 > 81.227.132.223.6112: P 
590518027:590518071(44) ack 2582330461 win 
64240\nE..Te.@.t..U.l6Q.......#2....<]P.........,................wakko0..........@......"

p re =~ src
p $~.to_a

Then you move the }x end of the regular expression and start 
uncommenting further bits until it starts to fail again, then you know 
where the problem is.
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