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920dae64 AT |
1 | package NDBM_File; |
2 | ||
3 | use strict; | |
4 | use warnings; | |
5 | ||
6 | require Tie::Hash; | |
7 | use XSLoader (); | |
8 | ||
9 | our @ISA = qw(Tie::Hash); | |
10 | our $VERSION = "1.06"; | |
11 | ||
12 | XSLoader::load 'NDBM_File', $VERSION; | |
13 | ||
14 | 1; | |
15 | ||
16 | __END__ | |
17 | ||
18 | =head1 NAME | |
19 | ||
20 | NDBM_File - Tied access to ndbm files | |
21 | ||
22 | =head1 SYNOPSIS | |
23 | ||
24 | use Fcntl; # For O_RDWR, O_CREAT, etc. | |
25 | use NDBM_File; | |
26 | ||
27 | tie(%h, 'NDBM_File', 'filename', O_RDWR|O_CREAT, 0666) | |
28 | or die "Couldn't tie NDBM file 'filename': $!; aborting"; | |
29 | ||
30 | # Now read and change the hash | |
31 | $h{newkey} = newvalue; | |
32 | print $h{oldkey}; | |
33 | ... | |
34 | ||
35 | untie %h; | |
36 | ||
37 | =head1 DESCRIPTION | |
38 | ||
39 | C<NDBM_File> establishes a connection between a Perl hash variable and | |
40 | a file in NDBM_File format;. You can manipulate the data in the file | |
41 | just as if it were in a Perl hash, but when your program exits, the | |
42 | data will remain in the file, to be used the next time your program | |
43 | runs. | |
44 | ||
45 | Use C<NDBM_File> with the Perl built-in C<tie> function to establish | |
46 | the connection between the variable and the file. The arguments to | |
47 | C<tie> should be: | |
48 | ||
49 | =over 4 | |
50 | ||
51 | =item 1. | |
52 | ||
53 | The hash variable you want to tie. | |
54 | ||
55 | =item 2. | |
56 | ||
57 | The string C<"NDBM_File">. (Ths tells Perl to use the C<NDBM_File> | |
58 | package to perform the functions of the hash.) | |
59 | ||
60 | =item 3. | |
61 | ||
62 | The name of the file you want to tie to the hash. | |
63 | ||
64 | =item 4. | |
65 | ||
66 | Flags. Use one of: | |
67 | ||
68 | =over 2 | |
69 | ||
70 | =item C<O_RDONLY> | |
71 | ||
72 | Read-only access to the data in the file. | |
73 | ||
74 | =item C<O_WRONLY> | |
75 | ||
76 | Write-only access to the data in the file. | |
77 | ||
78 | =item C<O_RDWR> | |
79 | ||
80 | Both read and write access. | |
81 | ||
82 | =back | |
83 | ||
84 | If you want to create the file if it does not exist, add C<O_CREAT> to | |
85 | any of these, as in the example. If you omit C<O_CREAT> and the file | |
86 | does not already exist, the C<tie> call will fail. | |
87 | ||
88 | =item 5. | |
89 | ||
90 | The default permissions to use if a new file is created. The actual | |
91 | permissions will be modified by the user's umask, so you should | |
92 | probably use 0666 here. (See L<perlfunc/umask>.) | |
93 | ||
94 | =back | |
95 | ||
96 | =head1 DIAGNOSTICS | |
97 | ||
98 | On failure, the C<tie> call returns an undefined value and probably | |
99 | sets C<$!> to contain the reason the file could not be tied. | |
100 | ||
101 | =head2 C<ndbm store returned -1, errno 22, key "..." at ...> | |
102 | ||
103 | This warning is emitted when you try to store a key or a value that | |
104 | is too long. It means that the change was not recorded in the | |
105 | database. See BUGS AND WARNINGS below. | |
106 | ||
107 | =head1 BUGS AND WARNINGS | |
108 | ||
109 | There are a number of limits on the size of the data that you can | |
110 | store in the NDBM file. The most important is that the length of a | |
111 | key, plus the length of its associated value, may not exceed 1008 | |
112 | bytes. | |
113 | ||
114 | See L<perlfunc/tie>, L<perldbmfilter>, L<Fcntl> | |
115 | ||
116 | =cut |