lib/perl5/5.6.1/AnyDBM_File.pm

   1 package AnyDBM_File;
   2
   3 use 5.005_64;
   4 our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;
   5
   6 my $mod;
   7 for $mod (@ISA) {
   8     if (eval "require $mod") {
   9         @ISA = ($mod);  # if we leave @ISA alone, warnings abound
  10         return 1;
  11     }
  12 }
  13
  14 die "No DBM package was successfully found or installed";
  15 #return 0;
  16
  17 =head1 NAME
  18
  19 AnyDBM_File - provide framework for multiple DBMs
  20
  21 NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations
  22
  23 =head1 SYNOPSIS
  24
  25     use AnyDBM_File;
  26
  27 =head1 DESCRIPTION
  28
  29 This module is a "pure virtual base class"--it has nothing of its own.
  30 It's just there to inherit from one of the various DBM packages.  It
  31 prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
  32 L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
  33 finally ODBM.   This way old programs that used to use NDBM via dbmopen()
  34 can still do so, but new ones can reorder @ISA:
  35
  36     BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
  37     use AnyDBM_File;
  38
  39 Having multiple DBM implementations makes it trivial to copy database formats:
  40
  41     use POSIX; use NDBM_File; use DB_File;
  42     tie %newhash,  'DB_File', $new_filename, O_CREAT|O_RDWR;
  43     tie %oldhash,  'NDBM_File', $old_filename, 1, 0;
  44     %newhash = %oldhash;
  45
  46 =head2 DBM Comparisons
  47
  48 Here's a partial table of features the different packages offer:
  49
  50                          odbm    ndbm    sdbm    gdbm    bsd-db
  51                          ----    ----    ----    ----    ------
  52  Linkage comes w/ perl   yes     yes     yes     yes     yes
  53  Src comes w/ perl       no      no      yes     no      no
  54  Comes w/ many unix os   yes     yes[0]  no      no      no
  55  Builds ok on !unix      ?       ?       yes     yes     ?
  56  Code Size               ?       ?       small   big     big
  57  Database Size           ?       ?       small   big?    ok[1]
  58  Speed                   ?       ?       slow    ok      fast
  59  FTPable                 no      no      yes     yes     yes
  60  Easy to build          N/A     N/A      yes     yes     ok[2]
  61  Size limits             1k      4k      1k[3]   none    none
  62  Byte-order independent  no      no      no      no      yes
  63  Licensing restrictions  ?       ?       no      yes     no
  64
  65
  66 =over 4
  67
  68 =item [0]
  69
  70 on mixed universe machines, may be in the bsd compat library,
  71 which is often shunned.
  72
  73 =item [1]
  74
  75 Can be trimmed if you compile for one access method.
  76
  77 =item [2]
  78
  79 See L<DB_File>.
  80 Requires symbolic links.
  81
  82 =item [3]
  83
  84 By default, but can be redefined.
  85
  86 =back
  87
  88 =head1 SEE ALSO
  89
  90 dbm(3), ndbm(3), DB_File(3), L<perldbmfilter>
  91
  92 =cut