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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 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