140 lines
3.7 KiB
Perl
140 lines
3.7 KiB
Perl
package SDBM_File;
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use strict;
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use warnings;
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require Tie::Hash;
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require XSLoader;
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our @ISA = qw(Tie::Hash);
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our $VERSION = "1.17";
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our @EXPORT_OK = qw(PAGFEXT DIRFEXT PAIRMAX);
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use Exporter "import";
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XSLoader::load();
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1;
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__END__
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=head1 NAME
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SDBM_File - Tied access to sdbm files
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=head1 SYNOPSIS
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use Fcntl; # For O_RDWR, O_CREAT, etc.
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use SDBM_File;
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tie(%h, 'SDBM_File', 'filename', O_RDWR|O_CREAT, 0666)
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or die "Couldn't tie SDBM file 'filename': $!; aborting";
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# Now read and change the hash
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$h{newkey} = newvalue;
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print $h{oldkey};
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...
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untie %h;
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=head1 DESCRIPTION
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C<SDBM_File> establishes a connection between a Perl hash variable and
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a file in SDBM_File format. You can manipulate the data in the file
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just as if it were in a Perl hash, but when your program exits, the
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data will remain in the file, to be used the next time your program
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runs.
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=head2 Tie
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Use C<SDBM_File> with the Perl built-in C<tie> function to establish
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the connection between the variable and the file.
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tie %hash, 'SDBM_File', $basename, $modeflags, $perms;
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tie %hash, 'SDBM_File', $dirfile, $modeflags, $perms, $pagfilename;
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C<$basename> is the base filename for the database. The database is two
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files with ".dir" and ".pag" extensions appended to C<$basename>,
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$basename.dir (or .sdbm_dir on VMS, per DIRFEXT constant)
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$basename.pag
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The two filenames can also be given separately in full as C<$dirfile>
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and C<$pagfilename>. This suits for two files without ".dir" and ".pag"
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extensions, perhaps for example two files from L<File::Temp>.
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C<$modeflags> can be the following constants from the C<Fcntl> module (in
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the style of the L<open(2)> system call),
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O_RDONLY read-only access
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O_WRONLY write-only access
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O_RDWR read and write access
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If you want to create the file if it does not already exist then bitwise-OR
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(C<|>) C<O_CREAT> too. If you omit C<O_CREAT> and the database does not
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already exist then the C<tie> call will fail.
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O_CREAT create database if doesn't already exist
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C<$perms> is the file permissions bits to use if new database files are
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created. This parameter is mandatory even when not creating a new database.
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The permissions will be reduced by the user's umask so the usual value here
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would be 0666, or if some very private data then 0600. (See
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L<perlfunc/umask>.)
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=head1 EXPORTS
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SDBM_File optionally exports the following constants:
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=over
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=item *
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C<PAGFEXT> - the extension used for the page file, usually C<.pag>.
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=item *
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C<DIRFEXT> - the extension used for the directory file, C<.dir>
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everywhere but VMS, where it is C<.sdbm_dir>.
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=item *
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C<PAIRMAX> - the maximum size of a stored hash entry, including the
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length of both the key and value.
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=back
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These constants can also be used with fully qualified names,
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eg. C<SDBM_File::PAGFEXT>.
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=head1 DIAGNOSTICS
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On failure, the C<tie> call returns an undefined value and probably
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sets C<$!> to contain the reason the file could not be tied.
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=head2 C<sdbm store returned -1, errno 22, key "..." at ...>
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This warning is emitted when you try to store a key or a value that
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is too long. It means that the change was not recorded in the
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database. See BUGS AND WARNINGS below.
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=head1 SECURITY WARNING
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B<Do not accept SDBM files from untrusted sources!>
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The sdbm file format was designed for speed and convenience, not for
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portability or security. A maliciously crafted file might cause perl to
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crash or even expose a security vulnerability.
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=head1 BUGS AND WARNINGS
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There are a number of limits on the size of the data that you can
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store in the SDBM file. The most important is that the length of a
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key, plus the length of its associated value, may not exceed 1008
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bytes.
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See L<perlfunc/tie>, L<perldbmfilter>, L<Fcntl>
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=cut
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