AnyDBM_File.pm revision 1.2 
1package AnyDBM_File;
2
3use vars qw(@ISA);
4@ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;
5
6my $mod;
7for $mod (@ISA) {
8    if (eval "require $mod") {
9	@ISA = ($mod);	# if we leave @ISA alone, warnings abound
10	return 1;
11    }
12}
13
14die "No DBM package was successfully found or installed";
15#return 0;
16
17=head1 NAME
18
19AnyDBM_File - provide framework for multiple DBMs
20
21NDBM_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
29This module is a "pure virtual base class"--it has nothing of its own.
30It's just there to inherit from one of the various DBM packages.  It
31prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
32L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
33finally ODBM.   This way old programs that used to use NDBM via dbmopen()
34can 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
39Having 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
48Here'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
70on mixed universe machines, may be in the bsd compat library,
71which is often shunned.
72
73=item [1]
74
75Can be trimmed if you compile for one access method.
76
77=item [2]
78
79See L<DB_File>.
80Requires symbolic links.
81
82=item [3]
83
84By default, but can be redefined.
85
86=back
87
88=head1 SEE ALSO
89
90dbm(3), ndbm(3), DB_File(3)
91
92=cut
93