my @data = <DATA>;

for (my $i=0; $i <= $#data -1; $i++)
{
   my @current = split(" ", $data[$i]);
   my @next = split(" ", $data[$i+1]);
   
   if ($current[2] eq $next[2]) {
    $data[$i] = undef;
   }  
}

print @data;


__DATA__
G1 X50 F30000
G1 X100 F30000
G1 X100 F3000