1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
|
package SDBM_File;
use strict;
use warnings;
require Tie::Hash;
require XSLoader;
our @ISA = qw(Tie::Hash);
our $VERSION = "1.11";
our @EXPORT_OK = qw(PAGFEXT DIRFEXT PAIRMAX);
use Exporter "import";
XSLoader::load();
1;
__END__
=head1 NAME
SDBM_File - Tied access to sdbm files
=head1 SYNOPSIS
use Fcntl; # For O_RDWR, O_CREAT, etc.
use SDBM_File;
tie(%h, 'SDBM_File', 'filename', O_RDWR|O_CREAT, 0666)
or die "Couldn't tie SDBM file 'filename': $!; aborting";
# Now read and change the hash
$h{newkey} = newvalue;
print $h{oldkey};
...
untie %h;
=head1 DESCRIPTION
C<SDBM_File> establishes a connection between a Perl hash variable and
a file in SDBM_File format. You can manipulate the data in the file
just as if it were in a Perl hash, but when your program exits, the
data will remain in the file, to be used the next time your program
runs.
=head2 Tie
Use C<SDBM_File> with the Perl built-in C<tie> function to establish
the connection between the variable and the file.
tie %hash, 'SDBM_File', $basename, $modeflags, $perms;
tie %hash, 'SDBM_File', $dirfile, $modeflags, $perms, $pagfilename;
C<$basename> is the base filename for the database. The database is two
files with ".dir" and ".pag" extensions appended to C<$basename>,
$basename.dir (or .sdbm_dir on VMS, per DIRFEXT constant)
$basename.pag
The two filenames can also be given separately in full as C<$dirfile>
and C<$pagfilename>. This suits for two files without ".dir" and ".pag"
extensions, perhaps for example two files from L<File::Temp>.
C<$modeflags> can be the following constants from the C<Fcntl> module (in
the style of the L<open(2)> system call),
O_RDONLY read-only access
O_WRONLY write-only access
O_RDWR read and write access
If you want to create the file if it does not already exist then bitwise-OR
(C<|>) C<O_CREAT> too. If you omit C<O_CREAT> and the database does not
already exist then the C<tie> call will fail.
O_CREAT create database if doesn't already exist
C<$perms> is the file permissions bits to use if new database files are
created. This parameter is mandatory even when not creating a new database.
The permissions will be reduced by the user's umask so the usual value here
would be 0666, or if some very private data then 0600. (See
L<perlfunc/umask>.)
=head1 EXPORTS
SDBM_File optionally exports the following constants:
=over
=item *
C<PAGFEXT> - the extension used for the page file, usually C<.pag>.
=item *
C<DIRFEXT> - the extension used for the directory file, C<.dir>
everywhere but VMS, where it is C<.sdbm_dir>.
=item *
C<PAIRMAX> - the maximum size of a stored hash entry, including the
length of both the key and value.
=back
These constants can also be used with fully qualified names,
eg. C<SDBM_File::PAGFEXT>.
=head1 DIAGNOSTICS
On failure, the C<tie> call returns an undefined value and probably
sets C<$!> to contain the reason the file could not be tied.
=head2 C<sdbm store returned -1, errno 22, key "..." at ...>
This warning is emitted when you try to store a key or a value that
is too long. It means that the change was not recorded in the
database. See BUGS AND WARNINGS below.
=head1 BUGS AND WARNINGS
There are a number of limits on the size of the data that you can
store in the SDBM file. The most important is that the length of a
key, plus the length of its associated value, may not exceed 1008
bytes.
See L<perlfunc/tie>, L<perldbmfilter>, L<Fcntl>
=cut
|
