use mapcar;

sub nCr {
    my( $r, @n )= @_;
    die "Usage: nCr($r,@n)"   if  @n < $r;
    my @pick= ( (0)x(@n-$r), (1)x$r );
    my @c;
    do {
        push @c, [mapcar{$_[0]?$_[1]:()}\@pick,\@n];
    } while(  nextpermute( @pick )  );
    return \@c;
}

for(  @{nCr(@ARGV)}  ) {
    print "[ ",join(", ",@$_)," ]\n";
}
__END__
> nCr 2 a b c
[ b, c ]
[ a, c ]
[ a, b ]