If you are trying to pass a reference to some value in a hash to a sub, that is possible. That way the sub wouldn't know the key name. More usual would be to pass a ref to the whole hash and the sub does know the key name. Here is a demo of both possibilities. Hope that I'm not confusing the issue. 
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dump qw(pp);
$!=1;

my %hash;
$hash{id1} = 001;
$hash{id2} = 002;
print "initial hash: ", pp (\%hash), "\n";

my $hash_ref = \%hash;

my $ref = \$hash{id2}; # A reference to id2

$$ref = 003;  #use ref to a scalar (value of id2)
print "modified hash: ", pp (\%hash), "\n";

modify_anon_hash_value ($ref);
print "mod by sub   : ", pp (\%hash), "\n";

more_normal_way($hash_ref);
print "mod more usual: ", pp ($hash_ref), "\n";


sub modify_anon_hash_value  #sub doesn't know which
{                           #key's value that it is
   my $ref = shift;         #modifying
   $$ref = 5;
}

sub more_normal_way  #usual pass the entire hash as ref
{
   my $href = shift;
   $href->{id2}=8;   #sub know which key to use
}
__END__
initial hash: { id1 => 1, id2 => 2 }
modified hash: { id1 => 1, id2 => 3 }
mod by sub   : { id1 => 1, id2 => 5 }
mod more usual: { id1 => 1, id2 => 8 }

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In reply to Re: Sub hash param by reference by Marshall
in thread Sub hash param by reference by hankcoder

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