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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
=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
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