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   1  package AnyDBM_File;
   2  
   3  use 5.006_001;
   4  our $VERSION = '1.00';
   5  our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;
   6  
   7  my $mod;
   8  for $mod (@ISA) {
   9      if (eval "require $mod") {
  10      @ISA = ($mod);    # if we leave @ISA alone, warnings abound
  11      return 1;
  12      }
  13  }
  14  
  15  die "No DBM package was successfully found or installed";
  16  #return 0;
  17  
  18  =head1 NAME
  19  
  20  AnyDBM_File - provide framework for multiple DBMs
  21  
  22  NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations
  23  
  24  =head1 SYNOPSIS
  25  
  26      use AnyDBM_File;
  27  
  28  =head1 DESCRIPTION
  29  
  30  This module is a "pure virtual base class"--it has nothing of its own.
  31  It's just there to inherit from one of the various DBM packages.  It
  32  prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
  33  L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
  34  finally ODBM.   This way old programs that used to use NDBM via dbmopen()
  35  can still do so, but new ones can reorder @ISA:
  36  
  37      BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
  38      use AnyDBM_File;
  39  
  40  Having multiple DBM implementations makes it trivial to copy database formats:
  41  
  42      use POSIX; use NDBM_File; use DB_File;
  43      tie %newhash,  'DB_File', $new_filename, O_CREAT|O_RDWR;
  44      tie %oldhash,  'NDBM_File', $old_filename, 1, 0;
  45      %newhash = %oldhash;
  46  
  47  =head2 DBM Comparisons
  48  
  49  Here's a partial table of features the different packages offer:
  50  
  51                           odbm    ndbm    sdbm    gdbm    bsd-db
  52               ----     ----    ----    ----    ------
  53   Linkage comes w/ perl   yes     yes     yes     yes     yes
  54   Src comes w/ perl       no      no      yes     no      no
  55   Comes w/ many unix os   yes     yes[0]  no      no      no
  56   Builds ok on !unix      ?       ?       yes     yes     ?
  57   Code Size               ?       ?       small   big     big
  58   Database Size           ?       ?       small   big?    ok[1]
  59   Speed                   ?       ?       slow    ok      fast
  60   FTPable                 no      no      yes     yes     yes
  61   Easy to build          N/A     N/A      yes     yes     ok[2]
  62   Size limits             1k      4k      1k[3]   none    none
  63   Byte-order independent  no      no      no      no      yes
  64   Licensing restrictions  ?       ?       no      yes     no
  65  
  66  
  67  =over 4
  68  
  69  =item [0] 
  70  
  71  on mixed universe machines, may be in the bsd compat library,
  72  which is often shunned.
  73  
  74  =item [1] 
  75  
  76  Can be trimmed if you compile for one access method.
  77  
  78  =item [2] 
  79  
  80  See L<DB_File>. 
  81  Requires symbolic links.  
  82  
  83  =item [3] 
  84  
  85  By default, but can be redefined.
  86  
  87  =back
  88  
  89  =head1 SEE ALSO
  90  
  91  dbm(3), ndbm(3), DB_File(3), L<perldbmfilter>
  92  
  93  =cut