From: Tim X <timx@...>
Date: 2007-03-30T13:50:05+09:00
Subject: Re: Regex problem... Tried Searching forum already... :(

James Edward Gray II <james@grayproductions.net> writes:

> On Mar 29, 2007, at 4:46 PM, Jon wrote:
>
>> I absolutely cannot figure out why this does not find a match! I tried
>> searching this forum before I posted... I've been stuck for hours on
>> such a simple problem... I feel retarded.
>
> No need to feel bad.  We will figure it out...
>
>> lines is an array of strings:
>>
>>   def go(lines)
>>     reg=/\[trace\-(\d+)\]/
>>
>>     lines.each do |line|
>>      puts line.slice!(0,25) #speed... some lines are long
>>      puts reg.match(line)[1]
>>     end
>>   end
>>
>>
>> Here is an example string:
>>
>> [trace-2932] Application=3071000
>
> First, let's be sure the expression matches:
>
>  >> "[trace-2932] Application=3071000" =~ /\[trace\-(\d+)\]/
> => 0
>
> Yep.  That's not our problem.
>
> So let's look into what slice!() is doing to your String:
>
>  >> str = "[trace-2932] Application=3071000"
> => "[trace-2932] Application=3071000"
>  >> str.slice!(0, 25)
> => "[trace-2932] Application="
>  >> str
> => "3071000"
>
> Bingo.  That's the problem.  See it now?
>
> Here is the documentation for slice!():
>
> $ ri -T String#slice!
> ---------------------------------------------------------- String#slice!
>       str.slice!(fixnum)           => fixnum or nil
>       str.slice!(fixnum, fixnum)   => new_str or nil
>       str.slice!(range)            => new_str or nil
>       str.slice!(regexp)           => new_str or nil
>       str.slice!(other_str)        => new_str or nil
> ------------------------------------------------------------------------
>       Deletes the specified portion from _str_, and returns the portion
>       deleted. The forms that take a +Fixnum+ will raise an +IndexError+
>       if the value is out of range; the +Range+ form will raise a
>       +RangeError+, and the +Regexp+ and +String+ forms will silently
>       ignore the assignment.
>
>          string = "this is a string"
>          string.slice!(2)        #=> 105
>          string.slice!(3..6)     #=> " is "
>          string.slice!(/s.*t/)   #=> "sa st"
>          string.slice!("r")      #=> "r"
>          string                  #=> "thing"
>
> Hope that helps.
>
> James Edward Gray II
>
>
>

I would also recommend anchoring your regexp. In fact, you will probably get
better performance by anchoring your RE and removing the splice (unless the
lines are a *LOT* longer than your example line). If you anchor your regexp to
the beginning of the line, the engine will stop trying to match as soon as it
cannot match the [trace-. To do this, start the regexp with a ^ i.e.
/^\[trace\-....

Tim

-- 
tcross (at) rapttech dot com dot au