AnyDBM_File.pm revision 1.1
1package AnyDBM_File; 2 3@ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA; 4 5eval { require NDBM_File } || 6eval { require DB_File } || 7eval { require GDBM_File } || 8eval { require SDBM_File } || 9eval { require ODBM_File }; 10 11=head1 NAME 12 13AnyDBM_File - provide framework for multiple DBMs 14 15NDBM_File, ODBM_File, SDBM_File, GDBM_File - various DBM implementations 16 17=head1 SYNOPSIS 18 19 use AnyDBM_File; 20 21=head1 DESCRIPTION 22 23This module is a "pure virtual base class"--it has nothing of its own. 24It's just there to inherit from one of the various DBM packages. It 25prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See 26L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and 27finally ODBM. This way old programs that used to use NDBM via dbmopen() 28can still do so, but new ones can reorder @ISA: 29 30 @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File); 31 32Note, however, that an explicit use overrides the specified order: 33 34 use GDBM_File; 35 @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File); 36 37will only find GDBM_File. 38 39Having multiple DBM implementations makes it trivial to copy database formats: 40 41 use POSIX; use NDBM_File; use DB_File; 42 tie %newhash, DB_File, $new_filename, O_CREAT|O_RDWR; 43 tie %oldhash, NDBM_File, $old_filename, 1, 0; 44 %newhash = %oldhash; 45 46=head2 DBM Comparisons 47 48Here's a partial table of features the different packages offer: 49 50 odbm ndbm sdbm gdbm bsd-db 51 ---- ---- ---- ---- ------ 52 Linkage comes w/ perl yes yes yes yes yes 53 Src comes w/ perl no no yes no no 54 Comes w/ many unix os yes yes[0] no no no 55 Builds ok on !unix ? ? yes yes ? 56 Code Size ? ? small big big 57 Database Size ? ? small big? ok[1] 58 Speed ? ? slow ok fast 59 FTPable no no yes yes yes 60 Easy to build N/A N/A yes yes ok[2] 61 Size limits 1k 4k 1k[3] none none 62 Byte-order independent no no no no yes 63 Licensing restrictions ? ? no yes no 64 65 66=over 4 67 68=item [0] 69 70on mixed universe machines, may be in the bsd compat library, 71which is often shunned. 72 73=item [1] 74 75Can be trimmed if you compile for one access method. 76 77=item [2] 78 79See L<DB_File>. 80Requires symbolic links. 81 82=item [3] 83 84By default, but can be redefined. 85 86=back 87 88=head1 SEE ALSO 89 90dbm(3), ndbm(3), DB_File(3) 91 92=cut 93