for (my $i = 0; $i < 3; $i++) { # array has 3 elements
    foreach my $key (keys @{$AoH[$i]}) {
        # DO STH
    }
}

##</code><code>##

@AoH = (
    {
       a  => "a1",
       b  => "b1",
       c   => "c1",
    },
    {
       d => "d1",
       e    => "e1",
       f     => "f1",
    },

    {
       g => "g1",
       h    => "h1",
       i     => "i1",
    },
  );