my (%hash);
$hash{'id1'} = "1";
doSub1(\%hash);

# the return id2 should be changed within doSub2 when doSub1 call it.
print "$hash{'id2'}\n";


doSub1 {
# accept param as hash by reference
my ($hrec_ref) = @_;
$$hrec_ref{'id2'} = "0";

# Going to call doSub2 by passing Only $$hrec_ref{'id2'} as reference.
# Because $hrec_ref is a hash reference already, How I can call it?
# doSub2(\$hrec_ref{'id2'}); Return Error. Not valid.
# doSub2($hrec_ref{'id2'}); Also return Error.

}


doSub2 {
# handle only a single string param by reference
my ($href) = @_;
$$href = "value changed in doSub2";
}
##</code><code>##

#... inside doSub1
my ($s) = $$hrec_ref{'id2'};
doSub2(\$s);
$$hrec_ref{'id2'} = $s;