From: Andrew Timberlake <andrew@...>
Date: 2008-01-16T13:25:34+09:00
Subject: Re: regex failure notifcation

> When i match a pattern and if it returns a nil, obviously the regex
> did not match the pattern. is there a way of identifying which set did
> not match
> pattern=Regexp.new('([g|l])\s+([0-9\.]+)')
> irb(main):073:0> pattern.match('g 32')
> => #<MatchData:0x2e158b4>
> irb(main):074:0> pattern.match('g we')
> => nil
> irb(main):075:0>
>
> If i can detect that the $2 failed and $1 was ok, i can pass more
> intelligent error messages.


You could change the regular expression to
pattern=Regexp.new('([g|l])?\s+([0-9\.]+)?')
m = pattern.match('g 32')
m[1] = 'g'
m[2] = '32'
m = pattern.match('g we')
m[1] = 'g'
m[2] = nil # <- Check for nil here to know that only the first part matched.
m = pattern.match('a 32')
m[1] = nil # <- First part failed
m[2] = '32'
m = pattern.match('32 g')
m = nil # <- The whole pattern failed

You'll have to check that this new regular expression correctly matches your
use case though.

Andrew Timberlake
andrew@andrewtimberlake.com
082 415 8283
skype: andrewtimberlake

"I have never let my schooling interfere with my education."
                                                --Mark Twain