print subtimes($string, 2, qr/(a)/,"<\$1\$1>");

sub subtimes {
    my ($string, $count, $find, $tosub) = @_;
    no strict "refs";
    
    my $newstring;
    while ($count--) {
        next unless $string =~ /($find)/;
        my ($num,%res) = 2;
        $res{$num++}=$$num while defined $$num;
        my ($matched, $startoffset, $endoffset, $temp) = ($1, $-[0], $+[0], $tosub);

        $temp =~ s/\$(\d+)/my $r=$1;$r++;$res{$r}/ge;
        $newstring .= substr($string, 0, $startoffset).$temp;
        substr($string, 0, $endoffset) = '';
    }
    return $newstring.$string;
}