rrds::create with unknown list of datasources

htb_collect.pl

# define a list of HTB classes to check
# the order matters, because of the RRD database
my @class_list=(100,200,300,400,999);

[..... truncated .... ]


        my $datasources = ""; 
        for my $class (0 .. $#class_list){
            $datasources .= "DS:$class_list[$class]:$storage_type:". $updatefreq * 10 .":0:U";
            $datasources .= ",\n" unless ($class == $#class_list);
        }   
        # datasource will contain
        # DS:100:COUNTER:600:0:U,DS:200:COUNTER:600:0:U,DS:300:COUNTER:600:0:U,DS:400:COUNTER:600:0:U,DS:999:COUNTER:600:0:U

        print $datasources."\n";

        RRDs::create($rrd_file,
                    "--start now",
                    "--step=$updatefreq", #data collection interval
                    "$datasources",
                    # 7 days of detailled records
                    "RRA:AVERAGE:0.5:1:".(7 * $day / $updatefreq). "", 
                    "RRA:MAX:0.5:1:".(7 * $day / $updatefreq). "", 
                    "RRA:LAST:0.5:1:1", # "last" value
                    # 1 record per hour for 60 days (1440 hours)
                    "RRA:AVERAGE:0.5:".($hour / $updatefreq).":1440",
                    "RRA:MAX:0.5:".($hour / $updatefreq).":1440",
                    # 1 record per 12 hours for 1 year (366 * 2 = 732 records)
                    "RRA:AVERAGE:0.5:".($day / 2 / $updatefreq).":732",
                    "RRA:MAX:0.5:".($day / 2 / $updatefreq).":732"
        ) or die "RRD Create error: $!";