Try this: 
#!/usr/bin/perl -w
use strict;
use Data::Dump qw(pp);

my %h =(
  siteA => {
            '10-9-11' => 3,
            '11-9-11' => 1,
            '12-9-11' => 2
            },
  siteB => {
             '04-04-11' =>5,
             '05-05-11' =>1,
           }
);

print "original:\n",pp(\%h),"\n";

$h{siteA}{'10-9-11'}++;
$h{siteB}{'04-04-11'}+=55;
$h{siteC}{'11-01-11'}=3;  #Wow!

print "Modifed Hash:\n",pp(\%h),"\n";

passing_hashref(\%h);
sub passing_hashref
{
   my $hashref = shift;
   $hashref->{SiteD}{'12-08-11'} = 33;
}

print "Modifed Hash via hashref subroutine:\n",pp(\%h),"\n";


__END__
original:
{
  siteA => { "10-9-11" => 3, "11-9-11" => 1, "12-9-11" => 2 },
  siteB => { "04-04-11" => 5, "05-05-11" => 1 },
}
Modifed Hash:
{
  siteA => { "10-9-11" => 4, "11-9-11" => 1, "12-9-11" => 2 },
  siteB => { "04-04-11" => 60, "05-05-11" => 1 },
  siteC => { "11-01-11" => 3 },
}
Modifed Hash via hashref subroutine:
{
  SiteD => { "12-08-11" => 33 },
  siteA => { "10-9-11" => 4, "11-9-11" => 1, "12-9-11" => 2 },
  siteB => { "04-04-11" => 60, "05-05-11" => 1 },
  siteC => { "11-01-11" => 3 },
}

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In reply to Re: Adding to a hash reference by Marshall
in thread Adding to a hash reference by Anonymous Monk

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