testrp.pl

use IO::Scalar;

my $scalar = <<HEAD;
This is a test of the code
Will it work?

That was a blank line, this should be part 2.
Is this part two?
HEAD

my $output = "";
my $seen_blank = undef;
my $io = new IO::Scalar \$scalar;
while (defined(my $line = $io->getline)) {
    if ($line =~ /^\s*$/) { # blank line
        $seen_blank = 'yes';
        next;
    }
    if (not defined $seen_blank) {
        # process the lines before the blank
        print ">> $line";
    } else {
        $output .= $line; # might need a "\n" here
    }
}
print "==rest==\n$output";