use Data::Dumper;
my @my_array = (1..7);
my $my_sub_array_length = 4;
print Dumper(combinations($my_sub_array_length, @my_array));
sub combinations {
    my($len,@a)=@_;
    return
        map{ my $c=$_<<1; [grep{($c>>=1)&1}@a]}
        &{sub{
            my @ret = ();
            my $x;
            for($_=(1<<shift)-1;
                ($x=$_)<1<<$_[0];
                $x&=~$x>>1,$x&=-$x,$_+=$x--,($x&=$_)?($_-=$x,$_+=$x/($
+x&-$x)):0
            ){ push @ret,$_ }
            @ret;
        }}($len,0+@a);
}
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