1package AnyDBM_File;
2use warnings;
3use strict;
4
5use 5.006_001;
6our $VERSION = '1.01';
7our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;
8
9my $mod;
10for $mod (@ISA) {
11    if (eval "require $mod") {
12	@ISA = ($mod);	# if we leave @ISA alone, warnings abound
13	return 1;
14    }
15}
16
17die "No DBM package was successfully found or installed";
18
19__END__
20
21=head1 NAME
22
23AnyDBM_File - provide framework for multiple DBMs
24
25=head1 SYNOPSIS
26
27    use AnyDBM_File;
28
29=head1 DESCRIPTION
30
31This module is a "pure virtual base class"--it has nothing of its own.
32It's just there to inherit from one of the various DBM packages.  It
33prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
34L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
35finally ODBM.   This way old programs that used to use NDBM via dbmopen()
36can still do so, but new ones can reorder @ISA:
37
38    BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
39    use AnyDBM_File;
40
41Having multiple DBM implementations makes it trivial to copy database formats:
42
43    use Fcntl; use NDBM_File; use DB_File;
44    tie %newhash,  'DB_File', $new_filename, O_CREAT|O_RDWR;
45    tie %oldhash,  'NDBM_File', $old_filename, 1, 0;
46    %newhash = %oldhash;
47
48=head2 DBM Comparisons
49
50Here's a partial table of features the different packages offer:
51
52                         odbm    ndbm    sdbm    gdbm    bsd-db
53			 ----	 ----    ----    ----    ------
54 Linkage comes w/ perl   yes     yes     yes     yes     yes
55 Src comes w/ perl       no      no      yes     no      no
56 Comes w/ many unix os   yes     yes[0]  no      no      no
57 Builds ok on !unix      ?       ?       yes     yes     ?
58 Code Size               ?       ?       small   big     big
59 Database Size           ?       ?       small   big?    ok[1]
60 Speed                   ?       ?       slow    ok      fast
61 FTPable                 no      no      yes     yes     yes
62 Easy to build          N/A     N/A      yes     yes     ok[2]
63 Size limits             1k      4k      1k[3]   none    none
64 Byte-order independent  no      no      no      no      yes
65 Licensing restrictions  ?       ?       no      yes     no
66
67
68=over 4
69
70=item [0]
71
72on mixed universe machines, may be in the bsd compat library,
73which is often shunned.
74
75=item [1]
76
77Can be trimmed if you compile for one access method.
78
79=item [2]
80
81See L<DB_File>.
82Requires symbolic links.
83
84=item [3]
85
86By default, but can be redefined.
87
88=back
89
90=head1 SEE ALSO
91
92dbm(3), ndbm(3), DB_File(3), L<perldbmfilter>
93
94=cut
95