1package AnyDBM_File; 2use warnings; 3use strict; 4 5use 5.006_001; 6our $VERSION = '1.01'; 7our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA; 8 9my $mod; 10for $mod (@ISA) { 11 if (eval "require $mod") { 12 @ISA = ($mod); # if we leave @ISA alone, warnings abound 13 return 1; 14 } 15} 16 17die "No DBM package was successfully found or installed"; 18 19__END__ 20 21=head1 NAME 22 23AnyDBM_File - provide framework for multiple DBMs 24 25NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations 26 27=head1 SYNOPSIS 28 29 use AnyDBM_File; 30 31=head1 DESCRIPTION 32 33This module is a "pure virtual base class"--it has nothing of its own. 34It's just there to inherit from one of the various DBM packages. It 35prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See 36L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and 37finally ODBM. This way old programs that used to use NDBM via dbmopen() 38can still do so, but new ones can reorder @ISA: 39 40 BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) } 41 use AnyDBM_File; 42 43Having multiple DBM implementations makes it trivial to copy database formats: 44 45 use Fcntl; use NDBM_File; use DB_File; 46 tie %newhash, 'DB_File', $new_filename, O_CREAT|O_RDWR; 47 tie %oldhash, 'NDBM_File', $old_filename, 1, 0; 48 %newhash = %oldhash; 49 50=head2 DBM Comparisons 51 52Here's a partial table of features the different packages offer: 53 54 odbm ndbm sdbm gdbm bsd-db 55 ---- ---- ---- ---- ------ 56 Linkage comes w/ perl yes yes yes yes yes 57 Src comes w/ perl no no yes no no 58 Comes w/ many unix os yes yes[0] no no no 59 Builds ok on !unix ? ? yes yes ? 60 Code Size ? ? small big big 61 Database Size ? ? small big? ok[1] 62 Speed ? ? slow ok fast 63 FTPable no no yes yes yes 64 Easy to build N/A N/A yes yes ok[2] 65 Size limits 1k 4k 1k[3] none none 66 Byte-order independent no no no no yes 67 Licensing restrictions ? ? no yes no 68 69 70=over 4 71 72=item [0] 73 74on mixed universe machines, may be in the bsd compat library, 75which is often shunned. 76 77=item [1] 78 79Can be trimmed if you compile for one access method. 80 81=item [2] 82 83See L<DB_File>. 84Requires symbolic links. 85 86=item [3] 87 88By default, but can be redefined. 89 90=back 91 92=head1 SEE ALSO 93 94dbm(3), ndbm(3), DB_File(3), L<perldbmfilter> 95 96=cut 97