#!/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;
';

my $cnt=0;
my @arr=();
for my $i (split(/(?<=;\n)/,$str))
{
  push(@arr,$i) && next unless(@arr);
  if($arr[-1] eq $i && $i=~/\$r->vor;\n/)
  { $cnt++; }
  else
  {
   if($cnt)
   {
    $arr[-1]='vor('.($cnt+1).");\n";
    $cnt=0;
   }
   push(@arr,$i);
  }
}

print join ('',@arr);

$str=$`.'vor('.scalar(@{[split(/;\n/,$&)]}).");\n".$' while($str=~/(?:\$r->vor;\n){2,}/s);