# DB_File.pm -- Perl 5 interface to Berkeley DB
#
# written by Paul Marquess (pmarquess@bfsec.bt.co.uk)
-# last modified 23rd June 1994
-# version 0.1
+# last modified 7th October 1995
+# version 1.0
package DB_File::HASHINFO ;
use Carp;
package DB_File ;
use Carp;
+$VERSION = 1.0 ;
+
#typedef enum { DB_BTREE, DB_HASH, DB_RECNO } DBTYPE;
$DB_BTREE = TIEHASH DB_File::BTREEINFO ;
$DB_HASH = TIEHASH DB_File::HASHINFO ;
require TieHash;
require Exporter;
-require AutoLoader;
+use AutoLoader;
require DynaLoader;
@ISA = qw(TieHash Exporter DynaLoader);
@EXPORT = qw(
);
sub AUTOLOAD {
- if (@_ > 1) {
- $AutoLoader::AUTOLOAD = $AUTOLOAD;
- goto &AutoLoader::AUTOLOAD;
- }
local($constname);
($constname = $AUTOLOAD) =~ s/.*:://;
$val = constant($constname, @_ ? $_[0] : 0);
1;
__END__
+
+=cut
+
+=head1 NAME
+
+DB_File - Perl5 access to Berkeley DB
+
+=head1 SYNOPSIS
+
+ use DB_File ;
+
+ [$X =] tie %hash, DB_File, $filename [, $flags, $mode, $DB_HASH] ;
+ [$X =] tie %hash, DB_File, $filename, $flags, $mode, $DB_BTREE ;
+ [$X =] tie @array, DB_File, $filename, $flags, $mode, $DB_RECNO ;
+
+ $status = $X->del($key [, $flags]) ;
+ $status = $X->put($key, $value [, $flags]) ;
+ $status = $X->get($key, $value [, $flags]) ;
+ $status = $X->seq($key, $value [, $flags]) ;
+ $status = $X->sync([$flags]) ;
+ $status = $X->fd ;
+
+ untie %hash ;
+ untie @array ;
+
+=head1 DESCRIPTION
+
+B<DB_File> is a module which allows Perl programs to make use of the
+facilities provided by Berkeley DB. If you intend to use this
+module you should really have a copy of the Berkeley DB manualpage at
+hand. The interface defined here mirrors the Berkeley DB interface
+closely.
+
+Berkeley DB is a C library which provides a consistent interface to a
+number of database formats. B<DB_File> provides an interface to all
+three of the database types currently supported by Berkeley DB.
+
+The file types are:
+
+=over 5
+
+=item DB_HASH
+
+This database type allows arbitrary key/data pairs to be stored in data
+files. This is equivalent to the functionality provided by other
+hashing packages like DBM, NDBM, ODBM, GDBM, and SDBM. Remember though,
+the files created using DB_HASH are not compatible with any of the
+other packages mentioned.
+
+A default hashing algorithm, which will be adequate for most
+applications, is built into Berkeley DB. If you do need to use your own
+hashing algorithm it is possible to write your own in Perl and have
+B<DB_File> use it instead.
+
+=item DB_BTREE
+
+The btree format allows arbitrary key/data pairs to be stored in a
+sorted, balanced binary tree.
+
+As with the DB_HASH format, it is possible to provide a user defined
+Perl routine to perform the comparison of keys. By default, though, the
+keys are stored in lexical order.
+
+=item DB_RECNO
+
+DB_RECNO allows both fixed-length and variable-length flat text files
+to be manipulated using the same key/value pair interface as in DB_HASH
+and DB_BTREE. In this case the key will consist of a record (line)
+number.
+
+=back
+
+=head2 How does DB_File interface to Berkeley DB?
+
+B<DB_File> allows access to Berkeley DB files using the tie() mechanism
+in Perl 5 (for full details, see L<perlfunc/tie()>). This facility
+allows B<DB_File> to access Berkeley DB files using either an
+associative array (for DB_HASH & DB_BTREE file types) or an ordinary
+array (for the DB_RECNO file type).
+
+In addition to the tie() interface, it is also possible to use most of
+the functions provided in the Berkeley DB API.
+
+=head2 Differences with Berkeley DB
+
+Berkeley DB uses the function dbopen() to open or create a database.
+Below is the C prototype for dbopen().
+
+ DB*
+ dbopen (const char * file, int flags, int mode,
+ DBTYPE type, const void * openinfo)
+
+The parameter C<type> is an enumeration which specifies which of the 3
+interface methods (DB_HASH, DB_BTREE or DB_RECNO) is to be used.
+Depending on which of these is actually chosen, the final parameter,
+I<openinfo> points to a data structure which allows tailoring of the
+specific interface method.
+
+This interface is handled slightly differently in B<DB_File>. Here is
+an equivalent call using B<DB_File>.
+
+ tie %array, DB_File, $filename, $flags, $mode, $DB_HASH ;
+
+The C<filename>, C<flags> and C<mode> parameters are the direct
+equivalent of their dbopen() counterparts. The final parameter $DB_HASH
+performs the function of both the C<type> and C<openinfo> parameters in
+dbopen().
+
+In the example above $DB_HASH is actually a reference to a hash
+object. B<DB_File> has three of these pre-defined references. Apart
+from $DB_HASH, there is also $DB_BTREE and $DB_RECNO.
+
+The keys allowed in each of these pre-defined references is limited to
+the names used in the equivalent C structure. So, for example, the
+$DB_HASH reference will only allow keys called C<bsize>, C<cachesize>,
+C<ffactor>, C<hash>, C<lorder> and C<nelem>.
+
+To change one of these elements, just assign to it like this
+
+ $DB_HASH{cachesize} = 10000 ;
+
+
+=head2 RECNO
+
+
+In order to make RECNO more compatible with Perl the array offset for all
+RECNO arrays begins at 0 rather than 1 as in Berkeley DB.
+
+
+=head2 In Memory Databases
+
+Berkeley DB allows the creation of in-memory databases by using NULL
+(that is, a C<(char *)0 in C) in place of the filename. B<DB_File>
+uses C<undef> instead of NULL to provide this functionality.
+
+
+=head2 Using the Berkeley DB Interface Directly
+
+As well as accessing Berkeley DB using a tied hash or array, it is also
+possible to make direct use of most of the functions defined in the
+Berkeley DB documentation.
+
+
+To do this you need to remember the return value from the tie.
+
+ $db = tie %hash, DB_File, "filename"
+
+Once you have done that, you can access the Berkeley DB API functions
+directly.
+
+ $db->put($key, $value, R_NOOVERWRITE) ;
+
+All the functions defined in L<dbx(3X)> are available except for
+close() and dbopen() itself. The B<DB_File> interface to these
+functions have been implemented to mirror the the way Berkeley DB
+works. In particular note that all the functions return only a status
+value. Whenever a Berkeley DB function returns data via one of its
+parameters, the B<DB_File> equivalent does exactly the same.
+
+All the constants defined in L<dbopen> are also available.
+
+Below is a list of the functions available.
+
+=over 5
+
+=item get
+
+Same as in C<recno> except that the flags parameter is optional.
+Remember the value associated with the key you request is returned in
+the $value parameter.
+
+=item put
+
+As usual the flags parameter is optional.
+
+If you use either the R_IAFTER or R_IBEFORE flags, the key parameter
+will have the record number of the inserted key/value pair set.
+
+=item del
+
+The flags parameter is optional.
+
+=item fd
+
+As in I<recno>.
+
+=item seq
+
+The flags parameter is optional.
+
+Both the key and value parameters will be set.
+
+=item sync
+
+The flags parameter is optional.
+
+=back
+
+=head1 EXAMPLES
+
+It is always a lot easier to understand something when you see a real
+example. So here are a few.
+
+=head2 Using HASH
+
+ use DB_File ;
+ use Fcntl ;
+
+ tie %h, "DB_File", "hashed", O_RDWR|O_CREAT, 0640, $DB_HASH ;
+
+ # Add a key/value pair to the file
+ $h{"apple"} = "orange" ;
+
+ # Check for existence of a key
+ print "Exists\n" if $h{"banana"} ;
+
+ # Delete
+ delete $h{"apple"} ;
+
+ untie %h ;
+
+=head2 Using BTREE
+
+Here is sample of code which used BTREE. Just to make life more
+interesting the default comparision function will not be used. Instead
+a Perl sub, C<Compare()>, will be used to do a case insensitive
+comparison.
+
+ use DB_File ;
+ use Fcntl ;
+
+ sub Compare
+ {
+ my ($key1, $key2) = @_ ;
+
+ "\L$key1" cmp "\L$key2" ;
+ }
+
+ $DB_BTREE->{compare} = 'Compare' ;
+
+ tie %h, 'DB_File', "tree", O_RDWR|O_CREAT, 0640, $DB_BTREE ;
+
+ # Add a key/value pair to the file
+ $h{'Wall'} = 'Larry' ;
+ $h{'Smith'} = 'John' ;
+ $h{'mouse'} = 'mickey' ;
+ $h{'duck'} = 'donald' ;
+
+ # Delete
+ delete $h{"duck"} ;
+
+ # Cycle through the keys printing them in order.
+ # Note it is not necessary to sort the keys as
+ # the btree will have kept them in order automatically.
+ foreach (keys %h)
+ { print "$_\n" }
+
+ untie %h ;
+
+Here is the output from the code above.
+
+ mouse
+ Smith
+ Wall
+
+
+=head2 Using RECNO
+
+ use DB_File ;
+ use Fcntl ;
+
+ $DB_RECNO->{psize} = 3000 ;
+
+ tie @h, DB_File, "text", O_RDWR|O_CREAT, 0640, $DB_RECNO ;
+
+ # Add a key/value pair to the file
+ $h[0] = "orange" ;
+
+ # Check for existence of a key
+ print "Exists\n" if $h[1] ;
+
+ untie @h ;
+
+
+
+=head1 CHANGES
+
+=head2 0.1
+
+First Release.
+
+=head2 0.2
+
+When B<DB_File> is opening a database file it no longer terminates the
+process if I<dbopen> returned an error. This allows file protection
+errors to be caught at run time. Thanks to Judith Grass
+<grass@cybercash.com> for spotting the bug.
+
+=head2 0.3
+
+Added prototype support for multiple btree compare callbacks.
+
+=head 1.0
+
+B<DB_File> has been in use for over a year. To reflect that, the
+version number has been incremented to 1.0.
+
+Added complete support for multiple concurrent callbacks.
+
+Using the I<push> method on an empty list didn't work properly. This
+has been fixed.
+
+=head1 WARNINGS
+
+If you happen find any other functions defined in the source for this
+module that have not been mentioned in this document -- beware. I may
+drop them at a moments notice.
+
+If you cannot find any, then either you didn't look very hard or the
+moment has passed and I have dropped them.
+
+=head1 BUGS
+
+Some older versions of Berkeley DB had problems with fixed length
+records using the RECNO file format. The newest version at the time of
+writing was 1.85 - this seems to have fixed the problems with RECNO.
+
+I am sure there are bugs in the code. If you do find any, or can
+suggest any enhancements, I would welcome your comments.
+
+=head1 AVAILABILITY
+
+Berkeley DB is available via the hold C<ftp.cs.berkeley.edu> in the
+directory C</ucb/4bsd/db.tar.gz>. It is I<not> under the GPL.
+
+=head1 SEE ALSO
+
+L<perl(1)>, L<dbopen(3)>, L<hash(3)>, L<recno(3)>, L<btree(3)>
+
+Berkeley DB is available from F<ftp.cs.berkeley.edu> in the directory
+F</ucb/4bsd>.
+
+=head1 AUTHOR
+
+The DB_File interface was written by Paul Marquess
+<pmarquess@bfsec.bt.co.uk>.
+Questions about the DB system itself may be addressed to Keith Bostic
+<bostic@cs.berkeley.edu>.
+
+=cut
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