The five minute introduction goes something like this.

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);
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This might seem a bit confusing since it is using a multi-dimensional array, but it's not really a big deal. The @{} part is used to specify that you want to deal with the entire column array, and not a specific element. A specific element is referenced as $data[$x][$y], such as $data[0][0] which is the first element of the first column.

Now to display this, it is quite simple. This will output something quite similar to your input file, though it is being read from the @data array.

for (my $i = 0; $i < @{$data[0]}; $i++)
{
     print "$data[0][$i],$data[1][$i]\n";
}
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The data structure is a little complicated because you want to have each column in a separate array. If instead you put each row into the array, it would be much simpler.