#!perl
use DBI; 
use strict; 
use warnings; 
use Data::Dump 'pp';

my $dbh = get_dbh(); # connect

# use hash to group data
my %logins=();
my $sql = 'SHOW GRANTS';
my $sth = $dbh->prepare($sql);
$sth->execute();
while (my ($result) = $sth->fetchrow_array()) {
  $result =~ s/['`]//g;
  if ($result =~ m/GRANT (.+?) ON (.+?) TO (\S+\@\S+)/i){
    push @{$logins{$3}{$2}},$1;
  }; 
}
pp \%logins;

# build array from hash
my @logins=();
for my $userhost (sort keys %logins){
  for my $db (sort keys %{$logins{$userhost}}){
    # join into one line here
    my $grant = join ',',@{$logins{$userhost}{$db}};
    my ($user,$host) = split '@',$userhost;
    push @logins,[$host,$user,$db,$grant];
  }
}
pp \@logins;