use strict;                   # Warns about mistakes (important)

my @data;                     # Data storage variable
my $filename = "data.dat";    # Filename constant

# Open a handle to the specified file, or die with a
# warning that it could not be done.
open (DAT, $filename) || die "Could not open $filename\n";

# Now read through the contents of the file
while (<DAT>)
{
     chomp;    # Removes trailing linefeed from input

     if ($_ eq "block")
     {
          # Put "block" into the two columns
          push (@{$data[0]}, $_);
          push (@{$data[1]}, $_);
     }
     elsif (/^\s*(\d+),(\d+)/)    # Look for " nn,nn"
     {
          # The first group of digits, expressed as "\d+",
          # is 'memorized' as $1, with the second group as
          # $2 (and so on). \s* means "0 or more spaces"
          # and is not memorized (ignored)
          push (@{$data[0]}, $1);
          push (@{$data[1]}, $2);
     }
     else
     {
          # $. is the current input line (perldoc perlvar)
          print "Invalid input line $.\n";
     }
}

close (DAT);

##</code><code>##

for (my $i = 0; $i < @{$data[0]}; $i++)
{
     print "$data[0][$i],$data[1][$i]\n";
}