sub foo {
  my ($text, $to) = @_;
  $text =~ s{(\d+)}{$to};
  $text;
}

print foo("123", 'capture 1 is $1');

##</code><code>##

sub bar {
  my ($text, $to) = @_;
  $text =~ s{(\d+)}{qq{qq{$to}}}ee;
  $text;
}

print bar("456", 'capture 1 is $1'); # prints capture 1 is 456