From: kane.sub@...
Date: 2007-05-31T00:17:23+09:00
Subject: Re: Substituting Variables

Hello Andrew,

Use double quotes and escape slashes.
'30 May 2007'.sub( /(\d+)\s(\w+)\s(\d+)/, "\\1 #{var} \\3" )

Wednesday, May 30, 2007, 8:09:29 PM, you wrote:

AS> Hello,

AS> I am running into difficulties trying to use a variable in a  
AS> substitution.  Here's an example:

AS> var = 'October'
AS> '30 May 2007'.sub( /(\d+)\s(\w+)\s(\d+)/, '\1 #{var} \3' )

AS> Here I would like to get '30 October 2007'.  The back-references,
AS> i.e. \1 and \3, only work within single quotation marks.  But the
AS> interpolation only works within double quotation marks.  What to do?

AS> Here's an example in IRB:

 >>> var = 'October'
 >>> re = /(\d+)\s(\w+)\s(\d+)/

 >>> '30 May 2007'.sub(re, '\1 #{var} \3')
=>> "30 \#{var} 2007"

 >>> '30 May 2007'.sub(re, "\1 #{var} \3")
=>> "\001 October \003"

 >>> '30 May 2007'.sub(re, "#{$1} #{var} #{$3}")
=>> "30 October 2007"

AS> Actually that last one does what I want -- but according to the  
AS> Pickaxe[1] $1 and friends aren't supposed to work and in fact it  
AS> doesn't work in my Ruby class.  So I think IRB is flattering to deceive.

AS> [1] String.gsub: "If a string is used as the replacement, special
AS> variables from the match (such as $& and $1) cannot be substituted
AS> into it, as substitution into the string occurs before the pattern
AS> match starts.  However, the sequences \1, \2, and so on may be used
AS> to interpolated successive groups in the match."

AS> I have found a workaround but I'm hoping there's a better way:

 >>> '30 May 2007'.sub(re, '\1' + " #{var} " + '\3')
=>> "30 October 2007"

AS> Any insight would be much appreciated.

AS> Thanks and regards,
AS> Andy Stewart



-- 
Best regards,
 kane                            mailto:kane.sub@inbox.uz