NAME
    DBD::Sys - System tables interface via DBI

SYNOPSIS
      use DBI;
      my $dbh = DBI->connect('DBI::Sys:');
      my $st  = $dbh->prepare('select distinct * from filesystems join filesysdf on mountpoint');
      my $num = $st->execute();
      if( $num > 0 )
      {
          while( my $row = $st->fetchrow_hashref() )
          {
              # ...
          }
      }

DESCRIPTION
    DBD::Sys is a so called database driver for DBI designed to request
    information from system tables using SQL. It's based on SQL::Statement
    as SQL engine and allows to be extended by DBD::Sys::Plugins.

  Prerequisites
    Of course, a DBD requires DBI to run. Further, SQL::Statement as SQL
    engine is required, Module::Pluggable to manage the plugin's and
    Module::Build for installation. Finally, to speed up some checks,
    Params::Util is needed.

    All these modules are mandatory and DBD::Sys will fail when they are not
    available.

    To request system information, existing modules from CPAN are used -
    there are available ones to provide access to some system tables. These
    modules are optional, but recommended. It wouldn't make much sense to
    use DBD::Sys without the ability to access the tables from the
    (operating) system.

    To get an overview which dependencies are there, please check the
    plugins or take a look into META.yml.

USAGE
  Installation
    We chose "Module::Build" installation, because not every system has a
    suitable make utility - but at least everyone who's using perl modules
    has a running perl. So installing can be done after extracting

      gzip -dc DBD-Sys-${VERSION}.tar.gz | tar xvf -

    without too much extra effort:

      1  cd DBD-Sys-${VERSION}
      2  perl Build.PL
      3  ./Build
      4  ./Build test
      5  ./Build install

    If you want to skip the tests (not recommended), you can skip over lines
    3 and 4.

  Fetching data
    To retrieve data, you can use the following example:

        my $dbh = DBI->connect('DBI:Sys:');
        $st  = $dbh->prepare( 'SELECT DISTINCT username, uid FROM pwent WHERE username=?' );
        $num = $st->execute(getlogin() || $ENV{USER} || $ENV{USERNAME});
        while( $row = $st->fetchrow_hashref() )
        {       
            printf( "Found result row: uid = %d, username = %s\n", $row->{uid}, $row->{username} );
        }

  Error handling
    Errors while processing statements are handled via DBI - read DBI
    documentation, especially the "err" and "errstr" documentation, if
    you're not familiar with error handling in DBI.

    Errors while modifying attributes, calling driver methods etc. are
    reported by throwing an exception using Carp.

  Metadata
    Each table implementor can request configurable meta data attributes.
    They will be accessible via the database handle:

        print $dbh->{"sys_" . lc $table . "_" . $attr}, "\n";
        # e.g.
        print DBI->neat( $dbh->{sys_filesysdf_blocksize} ), "\n";

BUGS & LIMITATIONS
    This module does not support any changes to the provided tables in order
    to prevent inconsistent data.

    The design of the plugins makes it less predictable what columns are
    provided in the end. Well, at least those columns from the tables
    provided by the DBD::Sys::Plugin::Meta and DBD::Sys::Plugin::Any will be
    available, even if they are not filled with data when the appropriate
    module is missing (e.g. if Sys::Filesystem is not available, the table
    "filesystems" gets the columns provided by
    DBD::Sys::Plugin::Any::Filesys, but no data at all).

    All additional table implementors must use the same primary key as all
    other implementors. To stay at the example of "filesystems", the primary
    key is *mountpoint* - and if any additional module provides another
    implementation (with data from another module than "Sys::Filesystem"),
    it needs to ensure that the column *mountpoint* is provided and unique.
    Additionally it must return *mountpoint* as primary key when it's method
    "getPrimaryKey" is invoked.

AUTHOR
        Jens Rehsack                        Alexander Breibach
        CPAN ID: REHSACK
        rehsack@cpan.org                    alexander.breibach@googlemail.com
        http://search.cpan.org/~rehsack/

COPYRIGHT
    This program is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.

    The full text of the license can be found in the LICENSE file included
    with this module.

SUPPORT
    Free support can be requested via regular CPAN bug-tracking system at
    <http://rt.cpan.org/NoAuth/Bugs.html?Dist=DBD-Sys>. There is no
    guaranteed reaction time or solution time, but it's always tried to give
    accept or reject a reported ticket within a week. It depends on business
    load. That doesn't mean that ticket via rt aren't handles as soon as
    possible, that means that soon depends on how much I have to do.

    Business and commercial support should be acquired from the authors via
    preferred freelancer agencies.

SEE ALSO
    perl(1), DBI, Module::Build, Module::Pluggable, Params::Util,
    SQL::Statement.