AnyDBM_File.pm revision 1.4 
1package AnyDBM_File;
2
3use 5.006_001;
4our $VERSION = '1.00';
5our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;
6
7my $mod;
8for $mod (@ISA) {
9    if (eval "require $mod") {
10	@ISA = ($mod);	# if we leave @ISA alone, warnings abound
11	return 1;
12    }
13}
14
15die "No DBM package was successfully found or installed";
16#return 0;
17
18=head1 NAME
19
20AnyDBM_File - provide framework for multiple DBMs
21
22NDBM_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
30This module is a "pure virtual base class"--it has nothing of its own.
31It's just there to inherit from one of the various DBM packages.  It
32prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
33L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
34finally ODBM.   This way old programs that used to use NDBM via dbmopen()
35can 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
40Having 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
49Here'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
71on mixed universe machines, may be in the bsd compat library,
72which is often shunned.
73
74=item [1]
75
76Can be trimmed if you compile for one access method.
77
78=item [2]
79
80See L<DB_File>.
81Requires symbolic links.
82
83=item [3]
84
85By default, but can be redefined.
86
87=back
88
89=head1 SEE ALSO
90
91dbm(3), ndbm(3), DB_File(3), L<perldbmfilter>
92
93=cut
94