use strict;
use warnings;
use File::Basename;
use IO::File;

my $iam = basename $0;
(my $fname = shift) or die "syntax:  $iam  <file>\n";
my $fh = new IO::File($fname) or die "$iam:  can't read $fname ($!)\n";

my $b_prev_blank = 0;    # Nonzero each time the previous line was blank
my $b_this_blank = 0;    # Nonzero each time the current line is blank
while (my $line = <$fh>) {
    chomp $line;
    $b_this_blank = ($line =~ /^\s*$/);
    (!$b_prev_blank or !$b_this_blank) and printf "%s\n", $line;
    $b_prev_blank = $b_this_blank;
}