package NDBM_File; use strict; use warnings; require Tie::Hash; require XSLoader; our @ISA = qw(Tie::Hash); our $VERSION = "1.15"; XSLoader::load(); 1; __END__ =head1 NAME NDBM_File - Tied access to ndbm files =head1 SYNOPSIS use Fcntl; # For O_RDWR, O_CREAT, etc. use NDBM_File; tie(%h, 'NDBM_File', 'filename', O_RDWR|O_CREAT, 0666) or die "Couldn't tie NDBM file 'filename': $!; aborting"; # Now read and change the hash $h{newkey} = newvalue; print $h{oldkey}; ... untie %h; =head1 DESCRIPTION C<NDBM_File> establishes a connection between a Perl hash variable and a file in NDBM_File format;. You can manipulate the data in the file just as if it were in a Perl hash, but when your program exits, the data will remain in the file, to be used the next time your program runs. Use C<NDBM_File> with the Perl built-in C<tie> function to establish the connection between the variable and the file. The arguments to C<tie> should be: =over 4 =item 1. The hash variable you want to tie. =item 2. The string C<"NDBM_File">. (Ths tells Perl to use the C<NDBM_File> package to perform the functions of the hash.) =item 3. The name of the file you want to tie to the hash. =item 4. Flags. Use one of: =over 2 =item C<O_RDONLY> Read-only access to the data in the file. =item C<O_WRONLY> Write-only access to the data in the file. =item C<O_RDWR> Both read and write access. =back If you want to create the file if it does not exist, add C<O_CREAT> to any of these, as in the example. If you omit C<O_CREAT> and the file does not already exist, the C<tie> call will fail. =item 5. The default permissions to use if a new file is created. The actual permissions will be modified by the user's umask, so you should probably use 0666 here. (See L<perlfunc/umask>.) =back =head1 DIAGNOSTICS On failure, the C<tie> call returns an undefined value and probably sets C<$!> to contain the reason the file could not be tied. =head2 C<ndbm 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 AND PORTABILITY B<Do not accept NDBM files from untrusted sources.> On modern Linux systems these are typically GDBM files, which are not portable across platforms. The GDBM documentation doesn't imply that files from untrusted sources can be safely used with C<libgdbm>. Systems that don't use GDBM compatibilty for ndbm support will be using a platform specific library, possibly inherited from BSD systems, where it may or may not be safe to use an untrusted file. 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 NDBM 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