lib/perl5/5.8.8/AnyDBM_File.pm

   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