From: matt@... (matt neuburg)
Date: 2009-03-18T05:17:30+09:00
Subject: Re: Interpolating $1, etc., from within a gsub block

Lloyd Zusman <ljz@asfast.com> wrote:

> I'm trying to use the block form of gsub in order to do substitution
> involving an interpolation stored within a variable, but I can't
> figure out how to get it to work.  Here's a simplified case of what
> I'm trying to do:
> 
> $fromre = Regexp.compile(ARGV[0])
> $repl   = ARGV[1]
> $replcount = 0
> 
> string = "... something arbitrary ..."
> 
> string.gsub!($fromre) {
>   |x|
>   $replcount += 1
>   $repl
> }
> 
> As you can see, the regexp comes in on the command line, as well as
> the replacement. I want to do this substution using the block form so
> I can count the number of replacements that were made.
> 
> This works as long as $repl doesn't contain any references to matched
> patterns. However, if this program is called 'myprog' and I do the
> following, the replacement of $1 with the indicated subexpression
> doesn't occur:
> 
> myprog 'abc(\S+)def' 'NEW-$1-MATCH'
> 
> In other words, if the string being substituted is this, "abcFOOBARdef",
> the result is not "NEW-FOOBAR-MATCH" as I would like it to be, but rather,
> "NEW-$1-MATCH".
> 

$fromre = /abc(\S+)def/
$repl = '"NEW-#{$1}-MATCH"'
string = "abcFOOBARdef"

string.gsub!($fromre) { |x|
  instance_eval($repl)
}

I don't like it any better than you do...! :) m.

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