$| = 1; 
 
while(<STDIN>){ 
    last if /^\s*$/; 
    chomp(); 
    s/^\s*subject\s*:\s*//i; 
    $subject = $_; 
} 
 
open( LOG, ">>$subject.log" ); 
 
$subject.='.rrd' if !/\.rrd$/; 
my $filename = $subject; 
 
print STDERR "$subject\n"; 
 
$last_reading = `rrdtool last $filename`; 
chomp($last_reading); 
 
while ($line =  <>) { 
    $orig = $line; 
    chomp($line); 
    $line =~ s/^.+?://; 
    print LOG $line."\n"; 
    @data = split /:/, $line; 
    next if(!$data[0]); 
    next if($data[0]<=$last_reading); 
    $cmd = "rrdtool update $filename $line"; 
    #print $cmd; 
    print `$cmd`; 
    print "$orig"    
}  
 
Can anyone help me in understanding what this script is doing?