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Edit File: SDBM_File.pm
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