From: Karl von Laudermann <doodpants@...>
Date: 2006-08-08T22:30:07+09:00
Subject: Re: value of $1is retained

Anders Vesterberg wrote:
> Hi
> I am using regexp in a loop to extract a value from a
> string. I have noticed that when string is nil $1 keeps its
> old value, which means that the expression after regexp
> does not get the correct value (which should be nil). The
> code looks like this
>
> (0..key_colnames.length-1).each do |i|
>   person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/
>   # assigning $1 to something
> end
>
> Shouldn't the $-variables be reset after each regexp? Or is
> it a better way to do this?

I know this doesn't answer your question as to why it works that way,
but you could instead write:

  (0..key_colnames.length-1).each do |i|
    if person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/
      # assigning $1 to something
    end
  end

or even:

  (0..key_colnames.length-1).each do |i|
    myvar = (person_data[key_colnames[i]] =~ /\"?([\w\-: ]*)\"?/) ?
      $1 :
      nil
  end

Incidentally, what version of Ruby are you using? I was unable to
reproduce this behavior on Ruby 1.8.4 on Windows. This sample program:

  "boom" =~ /(o)/
  puts "$1 = #{$1.inspect}"

  "boom" =~ /(a)/
  puts "$1 = #{$1.inspect}"

  "boom" =~ /(o)/
  puts "$1 = #{$1.inspect}"

yields this output: 

  $1 = "o"
  $1 = nil
  $1 = "o"