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package AnyDBM_File; |
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use 5.006_001; |
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our $VERSION = '1.00'; |
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our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA; |
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my $mod; |
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for $mod (@ISA) { |
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if (eval "require $mod") { |
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@ISA = ($mod); # if we leave @ISA alone, warnings abound |
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return 1; |
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} |
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} |
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die "No DBM package was successfully found or installed"; |
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#return 0; |
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=head1 NAME |
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AnyDBM_File - provide framework for multiple DBMs |
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NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations |
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=head1 SYNOPSIS |
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use AnyDBM_File; |
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=head1 DESCRIPTION |
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This module is a "pure virtual base class"--it has nothing of its own. |
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It's just there to inherit from one of the various DBM packages. It |
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prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See |
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L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and |
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finally ODBM. This way old programs that used to use NDBM via dbmopen() |
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can still do so, but new ones can reorder @ISA: |
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BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) } |
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use AnyDBM_File; |
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Having multiple DBM implementations makes it trivial to copy database formats: |
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use POSIX; use NDBM_File; use DB_File; |
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tie %newhash, 'DB_File', $new_filename, O_CREAT|O_RDWR; |
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tie %oldhash, 'NDBM_File', $old_filename, 1, 0; |
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%newhash = %oldhash; |
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=head2 DBM Comparisons |
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Here's a partial table of features the different packages offer: |
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odbm ndbm sdbm gdbm bsd-db |
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---- ---- ---- ---- ------ |
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Linkage comes w/ perl yes yes yes yes yes |
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Src comes w/ perl no no yes no no |
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Comes w/ many unix os yes yes[0] no no no |
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Builds ok on !unix ? ? yes yes ? |
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Code Size ? ? small big big |
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Database Size ? ? small big? ok[1] |
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Speed ? ? slow ok fast |
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FTPable no no yes yes yes |
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Easy to build N/A N/A yes yes ok[2] |
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Size limits 1k 4k 1k[3] none none |
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Byte-order independent no no no no yes |
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Licensing restrictions ? ? no yes no |
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=over 4 |
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=item [0] |
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on mixed universe machines, may be in the bsd compat library, |
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which is often shunned. |
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=item [1] |
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Can be trimmed if you compile for one access method. |
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=item [2] |
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See L<DB_File>. |
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Requires symbolic links. |
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=item [3] |
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By default, but can be redefined. |
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=back |
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=head1 SEE ALSO |
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dbm(3), ndbm(3), DB_File(3), L<perldbmfilter> |
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=cut |
