my $last;
my $i = 0;
while (<IN>) {
   chomp;
   $i++ if (!defined($last) || $_ ne $last);
   $last = $_;
   print OUT ("$_ $i\n");
}

##</code><code>##

perl -lpe "$i++ if ($_ ne $last); $last = $_; $_.=' '.$i;" inputfile > outputfile