use strict;
use warnings;
use Data::Dump 'pp';

my @words1 = ("", "",  "abcd", "efgh", "", "", "jklm", "nopq", "", "");
my @words2 = ("", ",", "abcd", "efgh", "", "", "jklm", "nopq", "");
my @words3 = ("", "", "abcd", "efgh", "", "jklm", "nopq", "", "", "rstu", "vwxy", "", "");

print "Double blancs:\n";
my @combined1 = process(@words1);
pp \@combined1;

print "\nArray doesn't start or end with double blancs:\n";
my @combined2 = process(@words2);
pp \@combined2;

print "\nArray contains single blanc:\n";
my @combined3 = process(@words3);
pp \@combined3;


sub process {
    my @input = @_;
    my @output = ();
    my $buffer = undef;
    my $last = shift @input;                    # We take the first element for whatever it is

    while ( defined(my $this = shift @input) ) {
        if ($last eq "" and $this eq "") {      # Double blancs
            
            # When we run into the first double blanc,
            # $buffer will be undef.
            # We don't want to push that.
            push @output, $buffer if defined $buffer;

            $buffer = "";
        }
        elsif ($this ne "") {                   # Non-blanc string
            # ($buffer || "") to prevent "undefined value in concatenation" warning
            $buffer = ($buffer || "") . $this;
        }
        
        $last = $this;
    }
    return @output;
}