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1 | package AnyDBM_File; |
2 | |
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3 | use 5.006_001; |
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4 | our $VERSION = '1.00'; |
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5 | our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA; |
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6 | |
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7 | my $mod; |
8 | for $mod (@ISA) { |
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9 | if (eval "require $mod") { |
10 | @ISA = ($mod); # if we leave @ISA alone, warnings abound |
11 | return 1; |
12 | } |
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13 | } |
14 | |
15 | die "No DBM package was successfully found or installed"; |
16 | #return 0; |
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17 | |
18 | =head1 NAME |
19 | |
20 | AnyDBM_File - provide framework for multiple DBMs |
21 | |
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22 | NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations |
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23 | |
24 | =head1 SYNOPSIS |
25 | |
26 | use AnyDBM_File; |
27 | |
28 | =head1 DESCRIPTION |
29 | |
30 | This module is a "pure virtual base class"--it has nothing of its own. |
31 | It's just there to inherit from one of the various DBM packages. It |
32 | prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See |
33 | L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and |
34 | finally ODBM. This way old programs that used to use NDBM via dbmopen() |
35 | can still do so, but new ones can reorder @ISA: |
36 | |
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37 | BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) } |
38 | use AnyDBM_File; |
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39 | |
40 | Having multiple DBM implementations makes it trivial to copy database formats: |
41 | |
42 | use POSIX; use NDBM_File; use DB_File; |
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43 | tie %newhash, 'DB_File', $new_filename, O_CREAT|O_RDWR; |
44 | tie %oldhash, 'NDBM_File', $old_filename, 1, 0; |
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45 | %newhash = %oldhash; |
46 | |
47 | =head2 DBM Comparisons |
48 | |
49 | Here'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 | |
71 | on mixed universe machines, may be in the bsd compat library, |
72 | which is often shunned. |
73 | |
74 | =item [1] |
75 | |
76 | Can be trimmed if you compile for one access method. |
77 | |
78 | =item [2] |
79 | |
80 | See L<DB_File>. |
81 | Requires symbolic links. |
82 | |
83 | =item [3] |
84 | |
85 | By default, but can be redefined. |
86 | |
87 | =back |
88 | |
89 | =head1 SEE ALSO |
90 | |
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91 | dbm(3), ndbm(3), DB_File(3), L<perldbmfilter> |
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92 | |
93 | =cut |