For purposes like this I am keeping a pair of functions in a private utility library (somewhat simplified): 
sub str_from_bits {
    my $vec = '';
    vec( $vec, $_, 1) = 1 for @_;
    $vec;
}

sub str_to_bits {
    my $vec = shift;
    grep vec( $vec, $_, 1), 0 .. 8*( length $vec);
}

[download]
str_from_bits() constructs a bit vector from a list of integers that are the indices of the one-bits in the string. str_to_bits() does the reverse. The function str_from_bits() applies directly to your problem: 
my $vec = str_from_bits( 8, 1, 9);
my ( $lo, $hi) = ( vec( $vec, 0, 8), vec( $vec, 1, 8));
printf "lo: 0x%02x, hi: 0x%02x\n", $lo, $hi;

[download]

The functions above are slightly simplified. There is also a num_from_bits() that returns an integer instead of a bit string. There would also be num_to_bits()<c>, but that is unified with <c>str_to_bits() as just to_bits() which checks its argument whether it's a string or number, similar to the bitwise boolean operators.

Together these functions cover most needs for bit manipulation that come up.

Anno

In reply to Re: Making two 8-bit numbers from indices of set bits by Anno
in thread Making two 8-bit numbers from indices of set bits by carcassonne

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