#!/usr/bin/perl

use strict;
use warnings;

my $str=
'$r->vor;
$r->vor;
$r->vor;
$r->drehe_rechts;
$r->vor;
$r->vor;
$r->drehe_links;
$r->vor;
$r->vor;
$r->vor;
$r->vor;
$r->vor;
drehe_um;
$r->vor;
';

$str =~ s!((?:\$r->vor;?\n?){2,})! my $anz = () = $1 =~ m/(\$r->vor;?\n?)/sg; my $string = "vor(".$anz.");\n"!esg;

print $str;