AnyDBM_File.pm revision 1.5 
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
22=head1 SYNOPSIS
23
24    use AnyDBM_File;
25
26=head1 DESCRIPTION
27
28This module is a "pure virtual base class"--it has nothing of its own.
29It's just there to inherit from one of the various DBM packages.  It
30prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
31L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
32finally ODBM.   This way old programs that used to use NDBM via dbmopen()
33can still do so, but new ones can reorder @ISA:
34
35    BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
36    use AnyDBM_File;
37
38Having multiple DBM implementations makes it trivial to copy database formats:
39
40    use POSIX; use NDBM_File; use DB_File;
41    tie %newhash,  'DB_File', $new_filename, O_CREAT|O_RDWR;
42    tie %oldhash,  'NDBM_File', $old_filename, 1, 0;
43    %newhash = %oldhash;
44
45=head2 DBM Comparisons
46
47Here's a partial table of features the different packages offer:
48
49                         odbm    ndbm    sdbm    gdbm    bsd-db
50			 ----	 ----    ----    ----    ------
51 Linkage comes w/ perl   yes     yes     yes     yes     yes
52 Src comes w/ perl       no      no      yes     no      no
53 Comes w/ many unix os   yes     yes[0]  no      no      no
54 Builds ok on !unix      ?       ?       yes     yes     ?
55 Code Size               ?       ?       small   big     big
56 Database Size           ?       ?       small   big?    ok[1]
57 Speed                   ?       ?       slow    ok      fast
58 FTPable                 no      no      yes     yes     yes
59 Easy to build          N/A     N/A      yes     yes     ok[2]
60 Size limits             1k      4k      1k[3]   none    none
61 Byte-order independent  no      no      no      no      yes
62 Licensing restrictions  ?       ?       no      yes     no
63
64
65=over 4
66
67=item [0]
68
69on mixed universe machines, may be in the bsd compat library,
70which is often shunned.
71
72=item [1]
73
74Can be trimmed if you compile for one access method.
75
76=item [2]
77
78See L<DB_File>.
79Requires symbolic links.
80
81=item [3]
82
83By default, but can be redefined.
84
85=back
86
87=head1 SEE ALSO
88
89dbm(3), ndbm(3), DB_File(3), L<perldbmfilter>
90
91=cut
92