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