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package SDBM_File;
use strict;
use warnings;
require Tie::Hash;
require XSLoader;
our @ISA = qw(Tie::Hash);
our $VERSION = "1.15";
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 SECURITY WARNING
B<Do not accept SDBM files from untrusted sources!>
The sdbm file format was designed for speed and convenience, not for
portability or security. A maliciously crafted file might cause perl to
crash or even expose a security vulnerability.
=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
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