Please see Re: Evaluating $1 construct in literal replacement expression to begin your journey.

Update: Or am I reading more into your question than you intend? Maybe just:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $string = 'hello $1';
 ;;
 if ('good morning all' =~ /good morning (\w+)/) {
   my $evaled_string = eval qq{ qq{$string} };
   print qq{>$evaled_string<};
   }
"
>hello all<
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See eval. ("After parsing a file and extracting the following line..." Note that using string eval in this way is a potentially dangerous operation.)