package AnyDBM_File;

use 5.006_001;
our $VERSION = '1.00';
our @ISA = qw(DB_File GDBM_File SDBM_File ODBM_File NDBM_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";
#return 0;

=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
Berkeley DB (See L<DB_File>), GDBM, SDBM (which is always there--it comes with
Perl), ODBM, and finally ndbm for compatibility reasons with Red Hat
Enterprise Linux 5.  This way foreign programs that used to use NDBM via
dbmopen() can still do so, but they have to reorder @ISA:

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

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

    use POSIX; 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