Hi Marshall, sorry I have confused your previous answer with my initial questions. Your previous answer is helpful. Just my initial case is little bit different. When inside a sub, the value pass in is already a hash reference and I would like to call another sub but only in refer to specific rec of that hash. Please have a look of the codes below;

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";
}
[download]

My problem confusing now is IF the hash is in a reference value and I need call another sub to process only specific hash rec. My current only way to deal with this is;

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

I'm trying to see if there are any shortcut version of coding it.