package AnyDBM_File;
use warnings;
use strict;

use 5.006_001;
our $VERSION = '1.01';
our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;

my $mod;
for $mod (@ISA) {
if (eval "require $mod") {
@ISA = ($mod); # if we leave @ISA alone, warnings abound
return 1;
}
}

die "No DBM package was successfully found or installed";

__END__

=head1 NAME

AnyDBM_File - provide framework for multiple DBMs

NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations

=head1 SYNOPSIS

use AnyDBM_File;

=head1 DESCRIPTION

This module is a "pure virtual base class"--it has nothing of its own.
It's just there to inherit from one of the various DBM packages. It
prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
finally ODBM. This way old programs that used to use NDBM via dbmopen()
can still do so, but new ones can reorder @ISA:

BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
use AnyDBM_File;

Having multiple DBM implementations makes it trivial to copy database formats:

use Fcntl; use NDBM_File; use DB_File;
tie %newhash, 'DB_File', $new_filename, O_CREAT|O_RDWR;
tie %oldhash, 'NDBM_File', $old_filename, 1, 0;
%newhash = %oldhash;

=head2 DBM Comparisons

Here's a partial table of features the different packages offer:

odbm ndbm sdbm gdbm bsd-db
---- ---- ---- ---- ------
Linkage comes w/ perl yes yes yes yes yes
Src comes w/ perl no no yes no no
Comes w/ many unix os yes yes[0] no no no
Builds ok on !unix ? ? yes yes ?
Code Size ? ? small big big
Database Size ? ? small big? ok[1]
Speed ? ? slow ok fast
FTPable no no yes yes yes
Easy to build N/A N/A yes yes ok[2]
Size limits 1k 4k 1k[3] none none
Byte-order independent no no no no yes
Licensing restrictions ? ? no yes no


=over 4

=item [0]

on mixed universe machines, may be in the bsd compat library,
which is often shunned.

=item [1]

Can be trimmed if you compile for one access method.

=item [2]

See L<DB_File>.
Requires symbolic links.

=item [3]

By default, but can be redefined.

=back

=head1 SEE ALSO

dbm(3), ndbm(3), DB_File(3), L<perldbmfilter>

=cut