Complex pattern matching

   foreach $KEY (keys %TAGLIST){
      while($text =~ m/$KEY/g){
         local $replace = '';
         eval(qq~\$replace = "$TAGLIST{$KEY}"~);
         die "$@ \nFailed String:$TAGLIST{$KEY}" if($@);
         $text =~ s/$&/$replace/;
      }
   }

$TAGLIST = 'Hi $KEY';
$KEY = 'John';

eval("\$prep = \"$TAGLIST\"");
die $@ if($@);

print $prep;

foreach $KEY (keys %TAGLIST){
   eval("\$text =~ s/$KEY/$TAGLIST{$KEY}/gis;");
   die "$@ \n Failed String: $TAGLIST{$KEY}" if($@);
}