93 lines
2.5 KiB
Perl
93 lines
2.5 KiB
Perl
package AnyDBM_File;
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use vars qw(@ISA);
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@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)
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=cut
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