From: James Edward Gray II <james@...>
Date: 2007-03-30T07:04:18+09:00
Subject: Re: Regex problem... Tried Searching forum already... :(

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