From: Daniel N <has.sox@...>
Date: 2006-08-08T18:37:03+09:00
Subject: Re: value of $1is retained

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On 8/8/06, Anders Vesterberg <anders1@vesdakon.se> 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?
>
> /Anders Vesterberg
> http://www.vesterberg.se


The problem is in your regex.  It will match a word containing hyphens or :
but it will also match an empty string!

>>
 a = /\"?([\w\-:]*)\"?/
=>
 /\"?([\w\-:]*)\"?/
>>
 "This is a String" =~ a
=>
 0
>>
 $1
=>
 "This"
>>
 "" =~ a
=>
 0
>>
 $1
=>
 ""
>>
 "$12dc" =~ a
=>
 0
>>
 $1
=> ""

Without knowing very much about the requirements of your regex, you need to
replace the * wildcard ( zero or more ) with + (one or more)

>>
 a = /\"?([\w\-:]+)\"?/
=>
 /\"?([\w\-:]+)\"?/
>>
 "This is a String" =~ a
=>
 0
>>
 $1
=>
 "This"
>>
 "" =~ a
=>
 nil
>>
 $1
=>
 nil
>>
 "$12dc" =~ a
=>
 1
>>
 $1
=> "12dc"

Nils as you would expect.  You could also make the first line it a touch
more rubyish ;)

key_colnames.each do |key|
 person_data[key] =~ /\"?([\w\-:])\"/
 # do your thing with $1
end

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