Forum: Ruby Regexp and using the matched value returned/found.

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Jean N. (Guest)
on 2009-04-13 07:56
Hi

I'm trying to do a regex search and using what I find a key to a Hash to
dig up some formatting info.

But what's happening is the literal \\1 or \\0 (or \1 \0) is not being
resolved to what's being found.

Any help would be awesome.

Ex: (Doesn't work)

   # regex looks like this: @swi_start = /SWI((dm)|(ph)|(ty)|(st))st/
   // executed in my code:
   line.gsub!( swi_start, self.colorize_token( '\\1' ) )
   # also not working: line.gsub!( swi_start, self.colorize_token( '\1'
) )

   def colorize_token( event )
      puts "Event: " << event
      return "<font color=\"#{@@color_list[ event ]}\"></font>"
   end

Output:
Event: \1

Ex: (This worked!!!)

  line.gsub!( swi_start, "#{@red_start}\\1#{@red_end}") then

Output:
<font color="red">dm</font>

Lastly please notes I've tried using " instead of ' in my method call
without any change.
Heesob P. (Guest)
on 2009-04-13 09:05
(Received via mailing list)
Hi,

2009/4/13 Jean N. <removed_email_address@domain.invalid>:
> Ex: (Doesn't work)
>   end
>
> Lastly please notes I've tried using " instead of ' in my method call
> without any change.

You should use block format in that case
Try
  line.gsub!(swi_start){colorize_token($1)}
or
  line.gsub!(swi_start){|x| colorize_token(x)}


Regards,

Park H.
Robert K. (Guest)
on 2009-04-13 15:45
(Received via mailing list)
On 13.04.2009 05:56, Jean N. wrote:
> I'm trying to do a regex search and using what I find a key to a Hash to
> dig up some formatting info.
>
> But what's happening is the literal \\1 or \\0 (or \1 \0) is not being
> resolved to what's being found.

Heesob gave you the solution already but I'd like to add a bit of
explanation why this is the solution.

> Any help would be awesome.
>
> Ex: (Doesn't work)
>
>    # regex looks like this: @swi_start = /SWI((dm)|(ph)|(ty)|(st))st/

The capturing groups are not needed.  This is sufficient:

/SWI(dm|ph|ty|st)st/

>    // executed in my code:
>    line.gsub!( swi_start, self.colorize_token( '\\1' ) )

You need to be aware that all method arguments are evaluated *before*
the method is actually invoked.  Since you need an argument for
#colorize which depends on the current match this can *never* work
because the #colorize is finished before #gsub! even starts matching.

>
> Ex: (This worked!!!)
>
>   line.gsub!( swi_start, "#{@red_start}\\1#{@red_end}") then

No, this does not do the same as you attempted to do with the code above
because in this case the replacement cannot depend on the match.  In
other words, you always insert the same color.

> Output:
> <font color="red">dm</font>
>
> Lastly please notes I've tried using " instead of ' in my method call
> without any change.

This is irrelevant in this case as the quote type does not affect the
time of evaluation (see above).

Kind regards

  robert
Jean N. (Guest)
on 2009-04-13 18:49
Excellent all

Thank you for the info. Using the block based notation worked much
better. (Also, Robert thank you for the additional info, very
informative).

My next question is:

Can someone direct me to a link to reading materials (my Google skills
seem to stink as I am not finding what I expect) on the pattern matching
variables I can use like $1 mentioned above as I am now trying to match
the WHOLE pattern and not just the "dm,ph,ty,st" portion.

So when I use:

line.gsub!(swi_start){colorize_token($1)}

The $1 only returns the aforementioned 2 char strings, I'd like to get
the whole thing "SWIdmst" or "SWItynd" etc etc.

Thanks.
lasitha (Guest)
on 2009-04-13 19:22
(Received via mailing list)
On Mon, Apr 13, 2009 at 8:19 PM, Jean N. <removed_email_address@domain.invalid>
wrote:
> [...]
> Can someone direct me to a link to reading materials (my Google skills
> seem to stink as I am not finding what I expect) on the pattern matching
> variables I can use like $1 mentioned above as I am now trying to match
> the WHOLE pattern and not just the "dm,ph,ty,st" portion.

The keywords seem to be 'ruby pre-defined variables'...
First two hits:
http://is.gd/saBm
http://is.gd/saDy

> [...]
> The $1 only returns the aforementioned 2 char strings, I'd like to get
> the whole thing "SWIdmst" or "SWItynd" etc etc.

$&

solidarity,
lasitha
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