Hash of Hashes

Create a hash of hashes via references:

The following two solutions are equivalent, except for the way the look.

Solution 1 :

$requiredPatches_href->{ $patch }->{ os } = $os;
$requiredPatches_href->{ $patch }->{ arch } = $arch;
$requiredPatches_href->{ $patch }->{ info } = $info;

Solution 2 : ( It is much clearer)

$requiredPatches_href->{ $patch } = {
os => $os,
arch => $arch,
info => $info,

};


Here is a small program to extract users their login name, uid,homedir and gid from /etc/passwd using HashOfHashes and hash reference:

#!/usr/bin/perl  -w

  sub func
  {
      my ( $login, $p, $uid, $gid, $gecos, $dir, $s );
      my %HoH = ();
      my $file = '/etc/passwd';
      open( PASSWD, "lt; $file" ) or die "Can't open $file : $!";
      while( <passwd> )
      {
          ( $login, $p, $uid, $gid, $gecos, $dir, $s ) = split( ':' );
#writing a hash of hash using reference
          $HoH{$login} =  {
                           'uid' => $uid,
                           'gid' => $gid,
                           'dir' => $dir,
                          };
      }
      close PASSWD;
      return \%HoH;

  }
  my $hash_ref = &func;

# Print the keys and values of a hash, given a hash reference

  while( my ($k, $v) = each %$hash_ref )
  {
# Print Outer hash HOH keys and values
      print "login: $k ";
# Print Inner hash keys and values for each outer hash key i.e login name
      while ( my ($key,$val) = each %$v )
      {
          print "$key:$val ";
      }
          print "\n";
  }

Output looks like this:

login: bin uid:2 dir:/bin gid:2
login: clamav uid:110 dir:/var/lib/clamav gid:120
login: nobody uid:65534 dir:/nonexistent gid:65534
login: lp uid:7 dir:/var/spool/lpd gid:7