| 1 | package AnyDBM_File;
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| 2 |
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| 3 | use 5.006_001;
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| 4 | our $VERSION = '1.00';
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| 5 | our @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;
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| 6 |
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| 7 | my $mod;
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| 8 | for $mod (@ISA) {
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| 9 | if (eval "require $mod") {
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| 10 | @ISA = ($mod); # if we leave @ISA alone, warnings abound
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| 11 | return 1;
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| 12 | }
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| 13 | }
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| 14 |
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| 15 | die "No DBM package was successfully found or installed";
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| 16 | #return 0;
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| 17 |
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| 18 | =head1 NAME
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| 19 |
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| 20 | AnyDBM_File - provide framework for multiple DBMs
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| 21 |
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| 22 | NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations
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| 23 |
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| 24 | =head1 SYNOPSIS
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| 25 |
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| 26 | use AnyDBM_File;
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| 27 |
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| 28 | =head1 DESCRIPTION
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| 29 |
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| 30 | This module is a "pure virtual base class"--it has nothing of its own.
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| 31 | It's just there to inherit from one of the various DBM packages. It
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| 32 | prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See
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| 33 | L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and
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| 34 | finally ODBM. This way old programs that used to use NDBM via dbmopen()
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| 35 | can still do so, but new ones can reorder @ISA:
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| 36 |
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| 37 | BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
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| 38 | use AnyDBM_File;
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| 39 |
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| 40 | Having multiple DBM implementations makes it trivial to copy database formats:
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| 41 |
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| 42 | use POSIX; use NDBM_File; use DB_File;
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| 43 | tie %newhash, 'DB_File', $new_filename, O_CREAT|O_RDWR;
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| 44 | tie %oldhash, 'NDBM_File', $old_filename, 1, 0;
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| 45 | %newhash = %oldhash;
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| 46 |
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| 47 | =head2 DBM Comparisons
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| 48 |
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| 49 | Here's a partial table of features the different packages offer:
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| 50 |
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| 51 | odbm ndbm sdbm gdbm bsd-db
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| 52 | ---- ---- ---- ---- ------
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| 53 | Linkage comes w/ perl yes yes yes yes yes
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| 54 | Src comes w/ perl no no yes no no
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| 55 | Comes w/ many unix os yes yes[0] no no no
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| 56 | Builds ok on !unix ? ? yes yes ?
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| 57 | Code Size ? ? small big big
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| 58 | Database Size ? ? small big? ok[1]
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| 59 | Speed ? ? slow ok fast
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| 60 | FTPable no no yes yes yes
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| 61 | Easy to build N/A N/A yes yes ok[2]
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| 62 | Size limits 1k 4k 1k[3] none none
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| 63 | Byte-order independent no no no no yes
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| 64 | Licensing restrictions ? ? no yes no
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| 65 |
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| 66 |
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| 67 | =over 4
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| 68 |
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| 69 | =item [0]
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| 70 |
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| 71 | on mixed universe machines, may be in the bsd compat library,
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| 72 | which is often shunned.
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| 73 |
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| 74 | =item [1]
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| 75 |
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| 76 | Can be trimmed if you compile for one access method.
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| 77 |
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| 78 | =item [2]
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| 79 |
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| 80 | See L<DB_File>.
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| 81 | Requires symbolic links.
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| 82 |
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| 83 | =item [3]
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| 84 |
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| 85 | By default, but can be redefined.
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| 86 |
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| 87 | =back
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| 88 |
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| 89 | =head1 SEE ALSO
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| 90 |
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| 91 | dbm(3), ndbm(3), DB_File(3), L<perldbmfilter>
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| 92 |
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| 93 | =cut
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