1 # DB_File.pm -- Perl 5 interface to Berkeley DB
3 # written by Paul Marquess (Paul.Marquess@btinternet.com)
4 # last modified 22nd July 1999
7 # Copyright (c) 1995-1999 Paul Marquess. All rights reserved.
8 # This program is free software; you can redistribute it and/or
9 # modify it under the same terms as Perl itself.
12 package DB_File::HASHINFO ;
19 @DB_File::HASHINFO::ISA = qw(Tie::Hash);
34 bless { VALID => { map {$_, 1}
35 qw( bsize ffactor nelem cachesize hash lorder)
47 return $self->{GOT}{$key} if exists $self->{VALID}{$key} ;
50 croak "${pkg}::FETCH - Unknown element '$key'" ;
60 if ( exists $self->{VALID}{$key} )
62 $self->{GOT}{$key} = $value ;
67 croak "${pkg}::STORE - Unknown element '$key'" ;
75 if ( exists $self->{VALID}{$key} )
77 delete $self->{GOT}{$key} ;
82 croak "DB_File::HASHINFO::DELETE - Unknown element '$key'" ;
90 exists $self->{VALID}{$key} ;
98 croak ref($self) . " does not define the method ${method}" ;
101 sub FIRSTKEY { my $self = shift ; $self->NotHere("FIRSTKEY") }
102 sub NEXTKEY { my $self = shift ; $self->NotHere("NEXTKEY") }
103 sub CLEAR { my $self = shift ; $self->NotHere("CLEAR") }
105 package DB_File::RECNOINFO ;
109 @DB_File::RECNOINFO::ISA = qw(DB_File::HASHINFO) ;
115 bless { VALID => { map {$_, 1}
116 qw( bval cachesize psize flags lorder reclen bfname )
122 package DB_File::BTREEINFO ;
126 @DB_File::BTREEINFO::ISA = qw(DB_File::HASHINFO) ;
132 bless { VALID => { map {$_, 1}
133 qw( flags cachesize maxkeypage minkeypage psize
134 compare prefix lorder )
144 use vars qw($VERSION @ISA @EXPORT $AUTOLOAD $DB_BTREE $DB_HASH $DB_RECNO $db_version) ;
150 #typedef enum { DB_BTREE, DB_HASH, DB_RECNO } DBTYPE;
151 $DB_BTREE = new DB_File::BTREEINFO ;
152 $DB_HASH = new DB_File::HASHINFO ;
153 $DB_RECNO = new DB_File::RECNOINFO ;
159 @ISA = qw(Tie::Hash Exporter DynaLoader);
161 $DB_BTREE $DB_HASH $DB_RECNO
196 ($constname = $AUTOLOAD) =~ s/.*:://;
197 my $val = constant($constname, @_ ? $_[0] : 0);
199 if ($! =~ /Invalid/ || $!{EINVAL}) {
200 $AutoLoader::AUTOLOAD = $AUTOLOAD;
201 goto &AutoLoader::AUTOLOAD;
204 my($pack,$file,$line) = caller;
205 croak "Your vendor has not defined DB macro $constname, used at $file line $line.
209 eval "sub $AUTOLOAD { $val }";
215 # Make all Fcntl O_XXX constants available for importing
217 my @O = grep /^O_/, @Fcntl::EXPORT;
218 Fcntl->import(@O); # first we import what we want to export
222 ## import borrowed from IO::File
223 ## exports Fcntl constants if available.
226 # my $callpkg = caller;
227 # Exporter::export $pkg, $callpkg, @_;
230 # Exporter::export 'Fcntl', $callpkg, '/^O_/';
234 bootstrap DB_File $VERSION;
236 # Preloaded methods go here. Autoload methods go after __END__, and are
237 # processed by the autosplit program.
239 sub tie_hash_or_array
242 my $tieHASH = ( (caller(1))[3] =~ /TIEHASH/ ) ;
244 $arg[4] = tied %{ $arg[4] }
245 if @arg >= 5 && ref $arg[4] && $arg[4] =~ /=HASH/ && tied %{ $arg[4] } ;
247 # make recno in Berkeley DB version 2 work like recno in version 1.
248 if ($db_version > 1 and defined $arg[4] and $arg[4] =~ /RECNO/ and
249 $arg[1] and ! -e $arg[1]) {
250 open(FH, ">$arg[1]") or return undef ;
252 chmod $arg[3] ? $arg[3] : 0666 , $arg[1] ;
255 DoTie_($tieHASH, @arg) ;
260 tie_hash_or_array(@_) ;
265 tie_hash_or_array(@_) ;
273 my $status = $self->seq($key, $value, R_FIRST());
276 while ($status == 0) {
278 $status = $self->seq($key, $value, R_NEXT());
280 foreach $key (reverse @keys) {
281 my $s = $self->del($key);
291 my $current_length = $self->length() ;
293 if ($length < $current_length) {
295 for ($key = $current_length - 1 ; $key >= $length ; -- $key)
298 elsif ($length > $current_length) {
299 $self->put($length-1, "") ;
305 croak "Usage: \$db->find_dup(key,value)\n"
309 my ($origkey, $value_wanted) = @_ ;
310 my ($key, $value) = ($origkey, 0);
313 for ($status = $db->seq($key, $value, R_CURSOR() ) ;
315 $status = $db->seq($key, $value, R_NEXT() ) ) {
317 return 0 if $key eq $origkey and $value eq $value_wanted ;
325 croak "Usage: \$db->del_dup(key,value)\n"
329 my ($key, $value) = @_ ;
330 my ($status) = $db->find_dup($key, $value) ;
331 return $status if $status != 0 ;
333 $status = $db->del($key, R_CURSOR() ) ;
339 croak "Usage: \$db->get_dup(key [,flag])\n"
340 unless @_ == 2 or @_ == 3 ;
347 my $wantarray = wantarray ;
353 # iterate through the database until either EOF ($status == 0)
354 # or a different key is encountered ($key ne $origkey).
355 for ($status = $db->seq($key, $value, R_CURSOR()) ;
356 $status == 0 and $key eq $origkey ;
357 $status = $db->seq($key, $value, R_NEXT()) ) {
359 # save the value or count number of matches
362 { ++ $values{$value} }
364 { push (@values, $value) }
371 return ($wantarray ? ($flag ? %values : @values) : $counter) ;
380 DB_File - Perl5 access to Berkeley DB version 1.x
386 [$X =] tie %hash, 'DB_File', [$filename, $flags, $mode, $DB_HASH] ;
387 [$X =] tie %hash, 'DB_File', $filename, $flags, $mode, $DB_BTREE ;
388 [$X =] tie @array, 'DB_File', $filename, $flags, $mode, $DB_RECNO ;
390 $status = $X->del($key [, $flags]) ;
391 $status = $X->put($key, $value [, $flags]) ;
392 $status = $X->get($key, $value [, $flags]) ;
393 $status = $X->seq($key, $value, $flags) ;
394 $status = $X->sync([$flags]) ;
398 $count = $X->get_dup($key) ;
399 @list = $X->get_dup($key) ;
400 %list = $X->get_dup($key, 1) ;
401 $status = $X->find_dup($key, $value) ;
402 $status = $X->del_dup($key, $value) ;
412 $old_filter = $db->filter_store_key ( sub { ... } ) ;
413 $old_filter = $db->filter_store_value( sub { ... } ) ;
414 $old_filter = $db->filter_fetch_key ( sub { ... } ) ;
415 $old_filter = $db->filter_fetch_value( sub { ... } ) ;
422 B<DB_File> is a module which allows Perl programs to make use of the
423 facilities provided by Berkeley DB version 1.x (if you have a newer
424 version of DB, see L<Using DB_File with Berkeley DB version 2>). It is
425 assumed that you have a copy of the Berkeley DB manual pages at hand
426 when reading this documentation. The interface defined here mirrors the
427 Berkeley DB interface closely.
429 Berkeley DB is a C library which provides a consistent interface to a
430 number of database formats. B<DB_File> provides an interface to all
431 three of the database types currently supported by Berkeley DB.
439 This database type allows arbitrary key/value pairs to be stored in data
440 files. This is equivalent to the functionality provided by other
441 hashing packages like DBM, NDBM, ODBM, GDBM, and SDBM. Remember though,
442 the files created using DB_HASH are not compatible with any of the
443 other packages mentioned.
445 A default hashing algorithm, which will be adequate for most
446 applications, is built into Berkeley DB. If you do need to use your own
447 hashing algorithm it is possible to write your own in Perl and have
448 B<DB_File> use it instead.
452 The btree format allows arbitrary key/value pairs to be stored in a
453 sorted, balanced binary tree.
455 As with the DB_HASH format, it is possible to provide a user defined
456 Perl routine to perform the comparison of keys. By default, though, the
457 keys are stored in lexical order.
461 DB_RECNO allows both fixed-length and variable-length flat text files
462 to be manipulated using the same key/value pair interface as in DB_HASH
463 and DB_BTREE. In this case the key will consist of a record (line)
468 =head2 Using DB_File with Berkeley DB version 2
470 Although B<DB_File> is intended to be used with Berkeley DB version 1,
471 it can also be used with version 2. In this case the interface is
472 limited to the functionality provided by Berkeley DB 1.x. Anywhere the
473 version 2 interface differs, B<DB_File> arranges for it to work like
474 version 1. This feature allows B<DB_File> scripts that were built with
475 version 1 to be migrated to version 2 without any changes.
477 If you want to make use of the new features available in Berkeley DB
478 2.x, use the Perl module B<BerkeleyDB> instead.
480 At the time of writing this document the B<BerkeleyDB> module is still
481 alpha quality (the version number is < 1.0), and so unsuitable for use
482 in any serious development work. Once its version number is >= 1.0, it
483 is considered stable enough for real work.
485 B<Note:> The database file format has changed in Berkeley DB version 2.
486 If you cannot recreate your databases, you must dump any existing
487 databases with the C<db_dump185> utility that comes with Berkeley DB.
488 Once you have rebuilt DB_File to use Berkeley DB version 2, your
489 databases can be recreated using C<db_load>. Refer to the Berkeley DB
490 documentation for further details.
492 Please read L<"COPYRIGHT"> before using version 2.x of Berkeley DB with
495 =head2 Interface to Berkeley DB
497 B<DB_File> allows access to Berkeley DB files using the tie() mechanism
498 in Perl 5 (for full details, see L<perlfunc/tie()>). This facility
499 allows B<DB_File> to access Berkeley DB files using either an
500 associative array (for DB_HASH & DB_BTREE file types) or an ordinary
501 array (for the DB_RECNO file type).
503 In addition to the tie() interface, it is also possible to access most
504 of the functions provided in the Berkeley DB API directly.
505 See L<THE API INTERFACE>.
507 =head2 Opening a Berkeley DB Database File
509 Berkeley DB uses the function dbopen() to open or create a database.
510 Here is the C prototype for dbopen():
513 dbopen (const char * file, int flags, int mode,
514 DBTYPE type, const void * openinfo)
516 The parameter C<type> is an enumeration which specifies which of the 3
517 interface methods (DB_HASH, DB_BTREE or DB_RECNO) is to be used.
518 Depending on which of these is actually chosen, the final parameter,
519 I<openinfo> points to a data structure which allows tailoring of the
520 specific interface method.
522 This interface is handled slightly differently in B<DB_File>. Here is
523 an equivalent call using B<DB_File>:
525 tie %array, 'DB_File', $filename, $flags, $mode, $DB_HASH ;
527 The C<filename>, C<flags> and C<mode> parameters are the direct
528 equivalent of their dbopen() counterparts. The final parameter $DB_HASH
529 performs the function of both the C<type> and C<openinfo> parameters in
532 In the example above $DB_HASH is actually a pre-defined reference to a
533 hash object. B<DB_File> has three of these pre-defined references.
534 Apart from $DB_HASH, there is also $DB_BTREE and $DB_RECNO.
536 The keys allowed in each of these pre-defined references is limited to
537 the names used in the equivalent C structure. So, for example, the
538 $DB_HASH reference will only allow keys called C<bsize>, C<cachesize>,
539 C<ffactor>, C<hash>, C<lorder> and C<nelem>.
541 To change one of these elements, just assign to it like this:
543 $DB_HASH->{'cachesize'} = 10000 ;
545 The three predefined variables $DB_HASH, $DB_BTREE and $DB_RECNO are
546 usually adequate for most applications. If you do need to create extra
547 instances of these objects, constructors are available for each file
550 Here are examples of the constructors and the valid options available
551 for DB_HASH, DB_BTREE and DB_RECNO respectively.
553 $a = new DB_File::HASHINFO ;
561 $b = new DB_File::BTREEINFO ;
571 $c = new DB_File::RECNOINFO ;
580 The values stored in the hashes above are mostly the direct equivalent
581 of their C counterpart. Like their C counterparts, all are set to a
582 default values - that means you don't have to set I<all> of the
583 values when you only want to change one. Here is an example:
585 $a = new DB_File::HASHINFO ;
586 $a->{'cachesize'} = 12345 ;
587 tie %y, 'DB_File', "filename", $flags, 0777, $a ;
589 A few of the options need extra discussion here. When used, the C
590 equivalent of the keys C<hash>, C<compare> and C<prefix> store pointers
591 to C functions. In B<DB_File> these keys are used to store references
592 to Perl subs. Below are templates for each of the subs:
598 # return the hash value for $data
604 my ($key, $key2) = @_ ;
606 # return 0 if $key1 eq $key2
607 # -1 if $key1 lt $key2
608 # 1 if $key1 gt $key2
609 return (-1 , 0 or 1) ;
614 my ($key, $key2) = @_ ;
616 # return number of bytes of $key2 which are
617 # necessary to determine that it is greater than $key1
621 See L<Changing the BTREE sort order> for an example of using the
624 If you are using the DB_RECNO interface and you intend making use of
625 C<bval>, you should check out L<The 'bval' Option>.
627 =head2 Default Parameters
629 It is possible to omit some or all of the final 4 parameters in the
630 call to C<tie> and let them take default values. As DB_HASH is the most
631 common file format used, the call:
633 tie %A, "DB_File", "filename" ;
637 tie %A, "DB_File", "filename", O_CREAT|O_RDWR, 0666, $DB_HASH ;
639 It is also possible to omit the filename parameter as well, so the
646 tie %A, "DB_File", undef, O_CREAT|O_RDWR, 0666, $DB_HASH ;
648 See L<In Memory Databases> for a discussion on the use of C<undef>
649 in place of a filename.
651 =head2 In Memory Databases
653 Berkeley DB allows the creation of in-memory databases by using NULL
654 (that is, a C<(char *)0> in C) in place of the filename. B<DB_File>
655 uses C<undef> instead of NULL to provide this functionality.
659 The DB_HASH file format is probably the most commonly used of the three
660 file formats that B<DB_File> supports. It is also very straightforward
663 =head2 A Simple Example
665 This example shows how to create a database, add key/value pairs to the
666 database, delete keys/value pairs and finally how to enumerate the
667 contents of the database.
671 use vars qw( %h $k $v ) ;
674 tie %h, "DB_File", "fruit", O_RDWR|O_CREAT, 0640, $DB_HASH
675 or die "Cannot open file 'fruit': $!\n";
677 # Add a few key/value pairs to the file
678 $h{"apple"} = "red" ;
679 $h{"orange"} = "orange" ;
680 $h{"banana"} = "yellow" ;
681 $h{"tomato"} = "red" ;
683 # Check for existence of a key
684 print "Banana Exists\n\n" if $h{"banana"} ;
686 # Delete a key/value pair.
689 # print the contents of the file
690 while (($k, $v) = each %h)
691 { print "$k -> $v\n" }
703 Note that the like ordinary associative arrays, the order of the keys
704 retrieved is in an apparently random order.
708 The DB_BTREE format is useful when you want to store data in a given
709 order. By default the keys will be stored in lexical order, but as you
710 will see from the example shown in the next section, it is very easy to
711 define your own sorting function.
713 =head2 Changing the BTREE sort order
715 This script shows how to override the default sorting algorithm that
716 BTREE uses. Instead of using the normal lexical ordering, a case
717 insensitive compare function will be used.
726 my ($key1, $key2) = @_ ;
727 "\L$key1" cmp "\L$key2" ;
730 # specify the Perl sub that will do the comparison
731 $DB_BTREE->{'compare'} = \&Compare ;
734 tie %h, "DB_File", "tree", O_RDWR|O_CREAT, 0640, $DB_BTREE
735 or die "Cannot open file 'tree': $!\n" ;
737 # Add a key/value pair to the file
738 $h{'Wall'} = 'Larry' ;
739 $h{'Smith'} = 'John' ;
740 $h{'mouse'} = 'mickey' ;
741 $h{'duck'} = 'donald' ;
746 # Cycle through the keys printing them in order.
747 # Note it is not necessary to sort the keys as
748 # the btree will have kept them in order automatically.
754 Here is the output from the code above.
760 There are a few point to bear in mind if you want to change the
761 ordering in a BTREE database:
767 The new compare function must be specified when you create the database.
771 You cannot change the ordering once the database has been created. Thus
772 you must use the same compare function every time you access the
777 =head2 Handling Duplicate Keys
779 The BTREE file type optionally allows a single key to be associated
780 with an arbitrary number of values. This option is enabled by setting
781 the flags element of C<$DB_BTREE> to R_DUP when creating the database.
783 There are some difficulties in using the tied hash interface if you
784 want to manipulate a BTREE database with duplicate keys. Consider this
790 use vars qw($filename %h ) ;
795 # Enable duplicate records
796 $DB_BTREE->{'flags'} = R_DUP ;
798 tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
799 or die "Cannot open $filename: $!\n";
801 # Add some key/value pairs to the file
802 $h{'Wall'} = 'Larry' ;
803 $h{'Wall'} = 'Brick' ; # Note the duplicate key
804 $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
805 $h{'Smith'} = 'John' ;
806 $h{'mouse'} = 'mickey' ;
808 # iterate through the associative array
809 # and print each key/value pair.
810 foreach (sort keys %h)
811 { print "$_ -> $h{$_}\n" }
823 As you can see 3 records have been successfully created with key C<Wall>
824 - the only thing is, when they are retrieved from the database they
825 I<seem> to have the same value, namely C<Larry>. The problem is caused
826 by the way that the associative array interface works. Basically, when
827 the associative array interface is used to fetch the value associated
828 with a given key, it will only ever retrieve the first value.
830 Although it may not be immediately obvious from the code above, the
831 associative array interface can be used to write values with duplicate
832 keys, but it cannot be used to read them back from the database.
834 The way to get around this problem is to use the Berkeley DB API method
835 called C<seq>. This method allows sequential access to key/value
836 pairs. See L<THE API INTERFACE> for details of both the C<seq> method
837 and the API in general.
839 Here is the script above rewritten using the C<seq> API method.
844 use vars qw($filename $x %h $status $key $value) ;
849 # Enable duplicate records
850 $DB_BTREE->{'flags'} = R_DUP ;
852 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
853 or die "Cannot open $filename: $!\n";
855 # Add some key/value pairs to the file
856 $h{'Wall'} = 'Larry' ;
857 $h{'Wall'} = 'Brick' ; # Note the duplicate key
858 $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
859 $h{'Smith'} = 'John' ;
860 $h{'mouse'} = 'mickey' ;
862 # iterate through the btree using seq
863 # and print each key/value pair.
865 for ($status = $x->seq($key, $value, R_FIRST) ;
867 $status = $x->seq($key, $value, R_NEXT) )
868 { print "$key -> $value\n" }
881 This time we have got all the key/value pairs, including the multiple
882 values associated with the key C<Wall>.
884 To make life easier when dealing with duplicate keys, B<DB_File> comes with
885 a few utility methods.
887 =head2 The get_dup() Method
889 The C<get_dup> method assists in
890 reading duplicate values from BTREE databases. The method can take the
893 $count = $x->get_dup($key) ;
894 @list = $x->get_dup($key) ;
895 %list = $x->get_dup($key, 1) ;
897 In a scalar context the method returns the number of values associated
898 with the key, C<$key>.
900 In list context, it returns all the values which match C<$key>. Note
901 that the values will be returned in an apparently random order.
903 In list context, if the second parameter is present and evaluates
904 TRUE, the method returns an associative array. The keys of the
905 associative array correspond to the values that matched in the BTREE
906 and the values of the array are a count of the number of times that
907 particular value occurred in the BTREE.
909 So assuming the database created above, we can use C<get_dup> like
915 use vars qw($filename $x %h ) ;
919 # Enable duplicate records
920 $DB_BTREE->{'flags'} = R_DUP ;
922 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
923 or die "Cannot open $filename: $!\n";
925 my $cnt = $x->get_dup("Wall") ;
926 print "Wall occurred $cnt times\n" ;
928 my %hash = $x->get_dup("Wall", 1) ;
929 print "Larry is there\n" if $hash{'Larry'} ;
930 print "There are $hash{'Brick'} Brick Walls\n" ;
932 my @list = sort $x->get_dup("Wall") ;
933 print "Wall => [@list]\n" ;
935 @list = $x->get_dup("Smith") ;
936 print "Smith => [@list]\n" ;
938 @list = $x->get_dup("Dog") ;
939 print "Dog => [@list]\n" ;
944 Wall occurred 3 times
946 There are 2 Brick Walls
947 Wall => [Brick Brick Larry]
951 =head2 The find_dup() Method
953 $status = $X->find_dup($key, $value) ;
955 This method checks for the existance of a specific key/value pair. If the
956 pair exists, the cursor is left pointing to the pair and the method
957 returns 0. Otherwise the method returns a non-zero value.
959 Assuming the database from the previous example:
964 use vars qw($filename $x %h $found) ;
966 my $filename = "tree" ;
968 # Enable duplicate records
969 $DB_BTREE->{'flags'} = R_DUP ;
971 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
972 or die "Cannot open $filename: $!\n";
974 $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
975 print "Larry Wall is $found there\n" ;
977 $found = ( $x->find_dup("Wall", "Harry") == 0 ? "" : "not") ;
978 print "Harry Wall is $found there\n" ;
986 Harry Wall is not there
989 =head2 The del_dup() Method
991 $status = $X->del_dup($key, $value) ;
993 This method deletes a specific key/value pair. It returns
994 0 if they exist and have been deleted successfully.
995 Otherwise the method returns a non-zero value.
997 Again assuming the existance of the C<tree> database
1002 use vars qw($filename $x %h $found) ;
1004 my $filename = "tree" ;
1006 # Enable duplicate records
1007 $DB_BTREE->{'flags'} = R_DUP ;
1009 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
1010 or die "Cannot open $filename: $!\n";
1012 $x->del_dup("Wall", "Larry") ;
1014 $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
1015 print "Larry Wall is $found there\n" ;
1022 Larry Wall is not there
1024 =head2 Matching Partial Keys
1026 The BTREE interface has a feature which allows partial keys to be
1027 matched. This functionality is I<only> available when the C<seq> method
1028 is used along with the R_CURSOR flag.
1030 $x->seq($key, $value, R_CURSOR) ;
1032 Here is the relevant quote from the dbopen man page where it defines
1033 the use of the R_CURSOR flag with seq:
1035 Note, for the DB_BTREE access method, the returned key is not
1036 necessarily an exact match for the specified key. The returned key
1037 is the smallest key greater than or equal to the specified key,
1038 permitting partial key matches and range searches.
1040 In the example script below, the C<match> sub uses this feature to find
1041 and print the first matching key/value pair given a partial key.
1047 use vars qw($filename $x %h $st $key $value) ;
1053 my $orig_key = $key ;
1054 $x->seq($key, $value, R_CURSOR) ;
1055 print "$orig_key\t-> $key\t-> $value\n" ;
1058 $filename = "tree" ;
1061 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
1062 or die "Cannot open $filename: $!\n";
1064 # Add some key/value pairs to the file
1065 $h{'mouse'} = 'mickey' ;
1066 $h{'Wall'} = 'Larry' ;
1067 $h{'Walls'} = 'Brick' ;
1068 $h{'Smith'} = 'John' ;
1072 print "IN ORDER\n" ;
1073 for ($st = $x->seq($key, $value, R_FIRST) ;
1075 $st = $x->seq($key, $value, R_NEXT) )
1077 { print "$key -> $value\n" }
1079 print "\nPARTIAL MATCH\n" ;
1099 a -> mouse -> mickey
1103 DB_RECNO provides an interface to flat text files. Both variable and
1104 fixed length records are supported.
1106 In order to make RECNO more compatible with Perl, the array offset for
1107 all RECNO arrays begins at 0 rather than 1 as in Berkeley DB.
1109 As with normal Perl arrays, a RECNO array can be accessed using
1110 negative indexes. The index -1 refers to the last element of the array,
1111 -2 the second last, and so on. Attempting to access an element before
1112 the start of the array will raise a fatal run-time error.
1114 =head2 The 'bval' Option
1116 The operation of the bval option warrants some discussion. Here is the
1117 definition of bval from the Berkeley DB 1.85 recno manual page:
1119 The delimiting byte to be used to mark the end of a
1120 record for variable-length records, and the pad charac-
1121 ter for fixed-length records. If no value is speci-
1122 fied, newlines (``\n'') are used to mark the end of
1123 variable-length records and fixed-length records are
1126 The second sentence is wrong. In actual fact bval will only default to
1127 C<"\n"> when the openinfo parameter in dbopen is NULL. If a non-NULL
1128 openinfo parameter is used at all, the value that happens to be in bval
1129 will be used. That means you always have to specify bval when making
1130 use of any of the options in the openinfo parameter. This documentation
1131 error will be fixed in the next release of Berkeley DB.
1133 That clarifies the situation with regards Berkeley DB itself. What
1134 about B<DB_File>? Well, the behavior defined in the quote above is
1135 quite useful, so B<DB_File> conforms to it.
1137 That means that you can specify other options (e.g. cachesize) and
1138 still have bval default to C<"\n"> for variable length records, and
1139 space for fixed length records.
1141 =head2 A Simple Example
1143 Here is a simple example that uses RECNO (if you are using a version
1144 of Perl earlier than 5.004_57 this example won't work -- see
1145 L<Extra RECNO Methods> for a workaround).
1150 my $filename = "text" ;
1154 tie @h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_RECNO
1155 or die "Cannot open file 'text': $!\n" ;
1157 # Add a few key/value pairs to the file
1162 push @h, "green", "black" ;
1164 my $elements = scalar @h ;
1165 print "The array contains $elements entries\n" ;
1168 print "popped $last\n" ;
1170 unshift @h, "white" ;
1171 my $first = shift @h ;
1172 print "shifted $first\n" ;
1174 # Check for existence of a key
1175 print "Element 1 Exists with value $h[1]\n" if $h[1] ;
1177 # use a negative index
1178 print "The last element is $h[-1]\n" ;
1179 print "The 2nd last element is $h[-2]\n" ;
1183 Here is the output from the script:
1185 The array contains 5 entries
1188 Element 1 Exists with value blue
1189 The last element is green
1190 The 2nd last element is yellow
1192 =head2 Extra RECNO Methods
1194 If you are using a version of Perl earlier than 5.004_57, the tied
1195 array interface is quite limited. In the example script above
1196 C<push>, C<pop>, C<shift>, C<unshift>
1197 or determining the array length will not work with a tied array.
1199 To make the interface more useful for older versions of Perl, a number
1200 of methods are supplied with B<DB_File> to simulate the missing array
1201 operations. All these methods are accessed via the object returned from
1204 Here are the methods:
1208 =item B<$X-E<gt>push(list) ;>
1210 Pushes the elements of C<list> to the end of the array.
1212 =item B<$value = $X-E<gt>pop ;>
1214 Removes and returns the last element of the array.
1216 =item B<$X-E<gt>shift>
1218 Removes and returns the first element of the array.
1220 =item B<$X-E<gt>unshift(list) ;>
1222 Pushes the elements of C<list> to the start of the array.
1224 =item B<$X-E<gt>length>
1226 Returns the number of elements in the array.
1230 =head2 Another Example
1232 Here is a more complete example that makes use of some of the methods
1233 described above. It also makes use of the API interface directly (see
1234 L<THE API INTERFACE>).
1237 use vars qw(@h $H $file $i) ;
1245 $H = tie @h, "DB_File", $file, O_RDWR|O_CREAT, 0640, $DB_RECNO
1246 or die "Cannot open file $file: $!\n" ;
1248 # first create a text file to play with
1256 # Print the records in order.
1258 # The length method is needed here because evaluating a tied
1259 # array in a scalar context does not return the number of
1260 # elements in the array.
1262 print "\nORIGINAL\n" ;
1263 foreach $i (0 .. $H->length - 1) {
1264 print "$i: $h[$i]\n" ;
1267 # use the push & pop methods
1270 print "\nThe last record was [$a]\n" ;
1272 # and the shift & unshift methods
1274 $H->unshift("first") ;
1275 print "The first record was [$a]\n" ;
1277 # Use the API to add a new record after record 2.
1279 $H->put($i, "Newbie", R_IAFTER) ;
1281 # and a new record before record 1.
1283 $H->put($i, "New One", R_IBEFORE) ;
1288 # now print the records in reverse order
1289 print "\nREVERSE\n" ;
1290 for ($i = $H->length - 1 ; $i >= 0 ; -- $i)
1291 { print "$i: $h[$i]\n" }
1293 # same again, but use the API functions instead
1294 print "\nREVERSE again\n" ;
1295 my ($s, $k, $v) = (0, 0, 0) ;
1296 for ($s = $H->seq($k, $v, R_LAST) ;
1298 $s = $H->seq($k, $v, R_PREV))
1299 { print "$k: $v\n" }
1304 and this is what it outputs:
1313 The last record was [four]
1314 The first record was [zero]
1338 Rather than iterating through the array, C<@h> like this:
1342 it is necessary to use either this:
1344 foreach $i (0 .. $H->length - 1)
1348 for ($a = $H->get($k, $v, R_FIRST) ;
1350 $a = $H->get($k, $v, R_NEXT) )
1354 Notice that both times the C<put> method was used the record index was
1355 specified using a variable, C<$i>, rather than the literal value
1356 itself. This is because C<put> will return the record number of the
1357 inserted line via that parameter.
1361 =head1 THE API INTERFACE
1363 As well as accessing Berkeley DB using a tied hash or array, it is also
1364 possible to make direct use of most of the API functions defined in the
1365 Berkeley DB documentation.
1367 To do this you need to store a copy of the object returned from the tie.
1369 $db = tie %hash, "DB_File", "filename" ;
1371 Once you have done that, you can access the Berkeley DB API functions
1372 as B<DB_File> methods directly like this:
1374 $db->put($key, $value, R_NOOVERWRITE) ;
1376 B<Important:> If you have saved a copy of the object returned from
1377 C<tie>, the underlying database file will I<not> be closed until both
1378 the tied variable is untied and all copies of the saved object are
1382 $db = tie %hash, "DB_File", "filename"
1383 or die "Cannot tie filename: $!" ;
1388 See L<The untie() Gotcha> for more details.
1390 All the functions defined in L<dbopen> are available except for
1391 close() and dbopen() itself. The B<DB_File> method interface to the
1392 supported functions have been implemented to mirror the way Berkeley DB
1393 works whenever possible. In particular note that:
1399 The methods return a status value. All return 0 on success.
1400 All return -1 to signify an error and set C<$!> to the exact
1401 error code. The return code 1 generally (but not always) means that the
1402 key specified did not exist in the database.
1404 Other return codes are defined. See below and in the Berkeley DB
1405 documentation for details. The Berkeley DB documentation should be used
1406 as the definitive source.
1410 Whenever a Berkeley DB function returns data via one of its parameters,
1411 the equivalent B<DB_File> method does exactly the same.
1415 If you are careful, it is possible to mix API calls with the tied
1416 hash/array interface in the same piece of code. Although only a few of
1417 the methods used to implement the tied interface currently make use of
1418 the cursor, you should always assume that the cursor has been changed
1419 any time the tied hash/array interface is used. As an example, this
1420 code will probably not do what you expect:
1422 $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
1423 or die "Cannot tie $filename: $!" ;
1425 # Get the first key/value pair and set the cursor
1426 $X->seq($key, $value, R_FIRST) ;
1428 # this line will modify the cursor
1429 $count = scalar keys %x ;
1431 # Get the second key/value pair.
1432 # oops, it didn't, it got the last key/value pair!
1433 $X->seq($key, $value, R_NEXT) ;
1435 The code above can be rearranged to get around the problem, like this:
1437 $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
1438 or die "Cannot tie $filename: $!" ;
1440 # this line will modify the cursor
1441 $count = scalar keys %x ;
1443 # Get the first key/value pair and set the cursor
1444 $X->seq($key, $value, R_FIRST) ;
1446 # Get the second key/value pair.
1448 $X->seq($key, $value, R_NEXT) ;
1452 All the constants defined in L<dbopen> for use in the flags parameters
1453 in the methods defined below are also available. Refer to the Berkeley
1454 DB documentation for the precise meaning of the flags values.
1456 Below is a list of the methods available.
1460 =item B<$status = $X-E<gt>get($key, $value [, $flags]) ;>
1462 Given a key (C<$key>) this method reads the value associated with it
1463 from the database. The value read from the database is returned in the
1464 C<$value> parameter.
1466 If the key does not exist the method returns 1.
1468 No flags are currently defined for this method.
1470 =item B<$status = $X-E<gt>put($key, $value [, $flags]) ;>
1472 Stores the key/value pair in the database.
1474 If you use either the R_IAFTER or R_IBEFORE flags, the C<$key> parameter
1475 will have the record number of the inserted key/value pair set.
1477 Valid flags are R_CURSOR, R_IAFTER, R_IBEFORE, R_NOOVERWRITE and
1480 =item B<$status = $X-E<gt>del($key [, $flags]) ;>
1482 Removes all key/value pairs with key C<$key> from the database.
1484 A return code of 1 means that the requested key was not in the
1487 R_CURSOR is the only valid flag at present.
1489 =item B<$status = $X-E<gt>fd ;>
1491 Returns the file descriptor for the underlying database.
1493 See L<Locking Databases> for an example of how to make use of the
1494 C<fd> method to lock your database.
1496 =item B<$status = $X-E<gt>seq($key, $value, $flags) ;>
1498 This interface allows sequential retrieval from the database. See
1499 L<dbopen> for full details.
1501 Both the C<$key> and C<$value> parameters will be set to the key/value
1502 pair read from the database.
1504 The flags parameter is mandatory. The valid flag values are R_CURSOR,
1505 R_FIRST, R_LAST, R_NEXT and R_PREV.
1507 =item B<$status = $X-E<gt>sync([$flags]) ;>
1509 Flushes any cached buffers to disk.
1511 R_RECNOSYNC is the only valid flag at present.
1517 A DBM Filter is a piece of code that is be used when you I<always>
1518 want to make the same transformation to all keys and/or values in a
1521 There are four methods associated with DBM Filters. All work identically,
1522 and each is used to install (or uninstall) a single DBM Filter. Each
1523 expects a single parameter, namely a reference to a sub. The only
1524 difference between them is the place that the filter is installed.
1530 =item B<filter_store_key>
1532 If a filter has been installed with this method, it will be invoked
1533 every time you write a key to a DBM database.
1535 =item B<filter_store_value>
1537 If a filter has been installed with this method, it will be invoked
1538 every time you write a value to a DBM database.
1541 =item B<filter_fetch_key>
1543 If a filter has been installed with this method, it will be invoked
1544 every time you read a key from a DBM database.
1546 =item B<filter_fetch_value>
1548 If a filter has been installed with this method, it will be invoked
1549 every time you read a value from a DBM database.
1553 You can use any combination of the methods, from none, to all four.
1555 All filter methods return the existing filter, if present, or C<undef>
1558 To delete a filter pass C<undef> to it.
1562 When each filter is called by Perl, a local copy of C<$_> will contain
1563 the key or value to be filtered. Filtering is achieved by modifying
1564 the contents of C<$_>. The return code from the filter is ignored.
1566 =head2 An Example -- the NULL termination problem.
1568 Consider the following scenario. You have a DBM database
1569 that you need to share with a third-party C application. The C application
1570 assumes that I<all> keys and values are NULL terminated. Unfortunately
1571 when Perl writes to DBM databases it doesn't use NULL termination, so
1572 your Perl application will have to manage NULL termination itself. When
1573 you write to the database you will have to use something like this:
1575 $hash{"$key\0"} = "$value\0" ;
1577 Similarly the NULL needs to be taken into account when you are considering
1578 the length of existing keys/values.
1580 It would be much better if you could ignore the NULL terminations issue
1581 in the main application code and have a mechanism that automatically
1582 added the terminating NULL to all keys and values whenever you write to
1583 the database and have them removed when you read from the database. As I'm
1584 sure you have already guessed, this is a problem that DBM Filters can
1591 my $filename = "/tmp/filt" ;
1594 my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
1595 or die "Cannot open $filename: $!\n" ;
1597 # Install DBM Filters
1598 $db->filter_fetch_key ( sub { s/\0$// } ) ;
1599 $db->filter_store_key ( sub { $_ .= "\0" } ) ;
1600 $db->filter_fetch_value( sub { s/\0$// } ) ;
1601 $db->filter_store_value( sub { $_ .= "\0" } ) ;
1603 $hash{"abc"} = "def" ;
1604 my $a = $hash{"ABC"} ;
1609 Hopefully the contents of each of the filters should be
1610 self-explanatory. Both "fetch" filters remove the terminating NULL,
1611 and both "store" filters add a terminating NULL.
1614 =head2 Another Example -- Key is a C int.
1616 Here is another real-life example. By default, whenever Perl writes to
1617 a DBM database it always writes the key and value as strings. So when
1620 $hash{12345} = "soemthing" ;
1622 the key 12345 will get stored in the DBM database as the 5 byte string
1623 "12345". If you actually want the key to be stored in the DBM database
1624 as a C int, you will have to use C<pack> when writing, and C<unpack>
1627 Here is a DBM Filter that does it:
1632 my $filename = "/tmp/filt" ;
1636 my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
1637 or die "Cannot open $filename: $!\n" ;
1639 $db->filter_fetch_key ( sub { $_ = unpack("i", $_) } ) ;
1640 $db->filter_store_key ( sub { $_ = pack ("i", $_) } ) ;
1641 $hash{123} = "def" ;
1646 This time only two filters have been used -- we only need to manipulate
1647 the contents of the key, so it wasn't necessary to install any value
1650 =head1 HINTS AND TIPS
1653 =head2 Locking Databases
1655 Concurrent access of a read-write database by several parties requires
1656 them all to use some kind of locking. Here's an example of Tom's that
1657 uses the I<fd> method to get the file descriptor, and then a careful
1658 open() to give something Perl will flock() for you. Run this repeatedly
1659 in the background to watch the locks granted in proper order.
1670 my($oldval, $fd, $db, %db, $value, $key);
1672 $key = shift || 'default';
1673 $value = shift || 'magic';
1677 $db = tie(%db, 'DB_File', '/tmp/foo.db', O_CREAT|O_RDWR, 0644)
1678 || die "dbcreat /tmp/foo.db $!";
1680 print "$$: db fd is $fd\n";
1681 open(DB_FH, "+<&=$fd") || die "dup $!";
1684 unless (flock (DB_FH, LOCK_SH | LOCK_NB)) {
1685 print "$$: CONTENTION; can't read during write update!
1686 Waiting for read lock ($!) ....";
1687 unless (flock (DB_FH, LOCK_SH)) { die "flock: $!" }
1689 print "$$: Read lock granted\n";
1691 $oldval = $db{$key};
1692 print "$$: Old value was $oldval\n";
1693 flock(DB_FH, LOCK_UN);
1695 unless (flock (DB_FH, LOCK_EX | LOCK_NB)) {
1696 print "$$: CONTENTION; must have exclusive lock!
1697 Waiting for write lock ($!) ....";
1698 unless (flock (DB_FH, LOCK_EX)) { die "flock: $!" }
1701 print "$$: Write lock granted\n";
1703 $db->sync; # to flush
1706 flock(DB_FH, LOCK_UN);
1710 print "$$: Updated db to $key=$value\n";
1712 =head2 Sharing Databases With C Applications
1714 There is no technical reason why a Berkeley DB database cannot be
1715 shared by both a Perl and a C application.
1717 The vast majority of problems that are reported in this area boil down
1718 to the fact that C strings are NULL terminated, whilst Perl strings are
1719 not. See L<DBM FILTERS> for a generic way to work around this problem.
1721 Here is a real example. Netscape 2.0 keeps a record of the locations you
1722 visit along with the time you last visited them in a DB_HASH database.
1723 This is usually stored in the file F<~/.netscape/history.db>. The key
1724 field in the database is the location string and the value field is the
1725 time the location was last visited stored as a 4 byte binary value.
1727 If you haven't already guessed, the location string is stored with a
1728 terminating NULL. This means you need to be careful when accessing the
1731 Here is a snippet of code that is loosely based on Tom Christiansen's
1732 I<ggh> script (available from your nearest CPAN archive in
1733 F<authors/id/TOMC/scripts/nshist.gz>).
1739 use vars qw( $dotdir $HISTORY %hist_db $href $binary_time $date ) ;
1740 $dotdir = $ENV{HOME} || $ENV{LOGNAME};
1742 $HISTORY = "$dotdir/.netscape/history.db";
1744 tie %hist_db, 'DB_File', $HISTORY
1745 or die "Cannot open $HISTORY: $!\n" ;;
1747 # Dump the complete database
1748 while ( ($href, $binary_time) = each %hist_db ) {
1750 # remove the terminating NULL
1751 $href =~ s/\x00$// ;
1753 # convert the binary time into a user friendly string
1754 $date = localtime unpack("V", $binary_time);
1755 print "$date $href\n" ;
1758 # check for the existence of a specific key
1759 # remember to add the NULL
1760 if ( $binary_time = $hist_db{"http://mox.perl.com/\x00"} ) {
1761 $date = localtime unpack("V", $binary_time) ;
1762 print "Last visited mox.perl.com on $date\n" ;
1765 print "Never visited mox.perl.com\n"
1770 =head2 The untie() Gotcha
1772 If you make use of the Berkeley DB API, it is I<very> strongly
1773 recommended that you read L<perltie/The untie Gotcha>.
1775 Even if you don't currently make use of the API interface, it is still
1778 Here is an example which illustrates the problem from a B<DB_File>
1787 $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_TRUNC
1788 or die "Cannot tie first time: $!" ;
1794 tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
1795 or die "Cannot tie second time: $!" ;
1799 When run, the script will produce this error message:
1801 Cannot tie second time: Invalid argument at bad.file line 14.
1803 Although the error message above refers to the second tie() statement
1804 in the script, the source of the problem is really with the untie()
1805 statement that precedes it.
1807 Having read L<perltie> you will probably have already guessed that the
1808 error is caused by the extra copy of the tied object stored in C<$X>.
1809 If you haven't, then the problem boils down to the fact that the
1810 B<DB_File> destructor, DESTROY, will not be called until I<all>
1811 references to the tied object are destroyed. Both the tied variable,
1812 C<%x>, and C<$X> above hold a reference to the object. The call to
1813 untie() will destroy the first, but C<$X> still holds a valid
1814 reference, so the destructor will not get called and the database file
1815 F<tst.fil> will remain open. The fact that Berkeley DB then reports the
1816 attempt to open a database that is alreday open via the catch-all
1817 "Invalid argument" doesn't help.
1819 If you run the script with the C<-w> flag the error message becomes:
1821 untie attempted while 1 inner references still exist at bad.file line 12.
1822 Cannot tie second time: Invalid argument at bad.file line 14.
1824 which pinpoints the real problem. Finally the script can now be
1825 modified to fix the original problem by destroying the API object
1834 $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
1838 =head1 COMMON QUESTIONS
1840 =head2 Why is there Perl source in my database?
1842 If you look at the contents of a database file created by DB_File,
1843 there can sometimes be part of a Perl script included in it.
1845 This happens because Berkeley DB uses dynamic memory to allocate
1846 buffers which will subsequently be written to the database file. Being
1847 dynamic, the memory could have been used for anything before DB
1848 malloced it. As Berkeley DB doesn't clear the memory once it has been
1849 allocated, the unused portions will contain random junk. In the case
1850 where a Perl script gets written to the database, the random junk will
1851 correspond to an area of dynamic memory that happened to be used during
1852 the compilation of the script.
1854 Unless you don't like the possibility of there being part of your Perl
1855 scripts embedded in a database file, this is nothing to worry about.
1857 =head2 How do I store complex data structures with DB_File?
1859 Although B<DB_File> cannot do this directly, there is a module which
1860 can layer transparently over B<DB_File> to accomplish this feat.
1862 Check out the MLDBM module, available on CPAN in the directory
1863 F<modules/by-module/MLDBM>.
1865 =head2 What does "Invalid Argument" mean?
1867 You will get this error message when one of the parameters in the
1868 C<tie> call is wrong. Unfortunately there are quite a few parameters to
1869 get wrong, so it can be difficult to figure out which one it is.
1871 Here are a couple of possibilities:
1877 Attempting to reopen a database without closing it.
1881 Using the O_WRONLY flag.
1885 =head2 What does "Bareword 'DB_File' not allowed" mean?
1887 You will encounter this particular error message when you have the
1888 C<strict 'subs'> pragma (or the full strict pragma) in your script.
1889 Consider this script:
1894 tie %x, DB_File, "filename" ;
1896 Running it produces the error in question:
1898 Bareword "DB_File" not allowed while "strict subs" in use
1900 To get around the error, place the word C<DB_File> in either single or
1901 double quotes, like this:
1903 tie %x, "DB_File", "filename" ;
1905 Although it might seem like a real pain, it is really worth the effort
1906 of having a C<use strict> in all your scripts.
1910 Articles that are either about B<DB_File> or make use of it.
1916 I<Full-Text Searching in Perl>, Tim Kientzle (tkientzle@ddj.com),
1917 Dr. Dobb's Journal, Issue 295, January 1999, pp 34-41
1923 Moved to the Changes file.
1927 Some older versions of Berkeley DB had problems with fixed length
1928 records using the RECNO file format. This problem has been fixed since
1929 version 1.85 of Berkeley DB.
1931 I am sure there are bugs in the code. If you do find any, or can
1932 suggest any enhancements, I would welcome your comments.
1936 B<DB_File> comes with the standard Perl source distribution. Look in
1937 the directory F<ext/DB_File>. Given the amount of time between releases
1938 of Perl the version that ships with Perl is quite likely to be out of
1939 date, so the most recent version can always be found on CPAN (see
1940 L<perlmod/CPAN> for details), in the directory
1941 F<modules/by-module/DB_File>.
1943 This version of B<DB_File> will work with either version 1.x or 2.x of
1944 Berkeley DB, but is limited to the functionality provided by version 1.
1946 The official web site for Berkeley DB is F<http://www.sleepycat.com>.
1947 Both versions 1 and 2 of Berkeley DB are available there.
1949 Alternatively, Berkeley DB version 1 is available at your nearest CPAN
1950 archive in F<src/misc/db.1.85.tar.gz>.
1952 If you are running IRIX, then get Berkeley DB version 1 from
1953 F<http://reality.sgi.com/ariel>. It has the patches necessary to
1954 compile properly on IRIX 5.3.
1958 Copyright (c) 1995-1999 Paul Marquess. All rights reserved. This program
1959 is free software; you can redistribute it and/or modify it under the
1960 same terms as Perl itself.
1962 Although B<DB_File> is covered by the Perl license, the library it
1963 makes use of, namely Berkeley DB, is not. Berkeley DB has its own
1964 copyright and its own license. Please take the time to read it.
1966 Here are are few words taken from the Berkeley DB FAQ (at
1967 http://www.sleepycat.com) regarding the license:
1969 Do I have to license DB to use it in Perl scripts?
1971 No. The Berkeley DB license requires that software that uses
1972 Berkeley DB be freely redistributable. In the case of Perl, that
1973 software is Perl, and not your scripts. Any Perl scripts that you
1974 write are your property, including scripts that make use of
1975 Berkeley DB. Neither the Perl license nor the Berkeley DB license
1976 place any restriction on what you may do with them.
1978 If you are in any doubt about the license situation, contact either the
1979 Berkeley DB authors or the author of DB_File. See L<"AUTHOR"> for details.
1984 L<perl(1)>, L<dbopen(3)>, L<hash(3)>, L<recno(3)>, L<btree(3)>,
1989 The DB_File interface was written by Paul Marquess
1990 E<lt>Paul.Marquess@btinternet.comE<gt>.
1991 Questions about the DB system itself may be addressed to
1992 E<lt>db@sleepycat.com<gt>.