#!/usr/bin/perl

use strict;
use warnings;

my @phrase = qw(Camel Perl Book);
my @subph  = ();

while(@phrase) {
    @subph = subphrases(@phrase);
    print +($_,$/) for (@subph);
    shift(@phrase);
}

sub subphrases {
    my $i = 0;
    my @sph = ();
    my @ph = (@_);
    while ($i < @phrase) {
        $sph[$i] = join (' ', map { $ph[$_]} (0..$i));
        $i++;
    }
    return (@sph);
}
__END__
Camel
Camel Perl
Camel Perl Book
Perl
Perl Book
Book