1 # DB_File.pm -- Perl 5 interface to Berkeley DB
3 # written by Paul Marquess (Paul.Marquess@btinternet.com)
4 # last modified 17th December 2000
7 # Copyright (c) 1995-2000 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 ;
20 @DB_File::HASHINFO::ISA = qw(Tie::Hash);
35 bless { VALID => { map {$_, 1}
36 qw( bsize ffactor nelem cachesize hash lorder)
48 return $self->{GOT}{$key} if exists $self->{VALID}{$key} ;
51 croak "${pkg}::FETCH - Unknown element '$key'" ;
61 if ( exists $self->{VALID}{$key} )
63 $self->{GOT}{$key} = $value ;
68 croak "${pkg}::STORE - Unknown element '$key'" ;
76 if ( exists $self->{VALID}{$key} )
78 delete $self->{GOT}{$key} ;
83 croak "DB_File::HASHINFO::DELETE - Unknown element '$key'" ;
91 exists $self->{VALID}{$key} ;
99 croak ref($self) . " does not define the method ${method}" ;
102 sub FIRSTKEY { my $self = shift ; $self->NotHere("FIRSTKEY") }
103 sub NEXTKEY { my $self = shift ; $self->NotHere("NEXTKEY") }
104 sub CLEAR { my $self = shift ; $self->NotHere("CLEAR") }
106 package DB_File::RECNOINFO ;
111 @DB_File::RECNOINFO::ISA = qw(DB_File::HASHINFO) ;
117 bless { VALID => { map {$_, 1}
118 qw( bval cachesize psize flags lorder reclen bfname )
124 package DB_File::BTREEINFO ;
129 @DB_File::BTREEINFO::ISA = qw(DB_File::HASHINFO) ;
135 bless { VALID => { map {$_, 1}
136 qw( flags cachesize maxkeypage minkeypage psize
137 compare prefix lorder )
148 use vars qw($VERSION @ISA @EXPORT $AUTOLOAD $DB_BTREE $DB_HASH $DB_RECNO
149 $db_version $use_XSLoader
156 #typedef enum { DB_BTREE, DB_HASH, DB_RECNO } DBTYPE;
157 $DB_BTREE = new DB_File::BTREEINFO ;
158 $DB_HASH = new DB_File::HASHINFO ;
159 $DB_RECNO = new DB_File::RECNOINFO ;
166 eval { require XSLoader } ;
171 @ISA = qw(DynaLoader);
175 push @ISA, qw(Tie::Hash Exporter);
177 $DB_BTREE $DB_HASH $DB_RECNO
212 ($constname = $AUTOLOAD) =~ s/.*:://;
213 my $val = constant($constname, @_ ? $_[0] : 0);
215 if ($! =~ /Invalid/ || $!{EINVAL}) {
216 $AutoLoader::AUTOLOAD = $AUTOLOAD;
217 goto &AutoLoader::AUTOLOAD;
220 my($pack,$file,$line) = caller;
221 croak "Your vendor has not defined DB macro $constname, used at $file line $line.
225 eval "sub $AUTOLOAD { $val }";
231 # Make all Fcntl O_XXX constants available for importing
233 my @O = grep /^O_/, @Fcntl::EXPORT;
234 Fcntl->import(@O); # first we import what we want to export
239 { XSLoader::load("DB_File", $VERSION)}
241 { bootstrap DB_File $VERSION }
243 # Preloaded methods go here. Autoload methods go after __END__, and are
244 # processed by the autosplit program.
246 sub tie_hash_or_array
249 my $tieHASH = ( (caller(1))[3] =~ /TIEHASH/ ) ;
251 $arg[4] = tied %{ $arg[4] }
252 if @arg >= 5 && ref $arg[4] && $arg[4] =~ /=HASH/ && tied %{ $arg[4] } ;
254 # make recno in Berkeley DB version 2 work like recno in version 1.
255 if ($db_version > 1 and defined $arg[4] and $arg[4] =~ /RECNO/ and
256 $arg[1] and ! -e $arg[1]) {
257 open(FH, ">$arg[1]") or return undef ;
259 chmod $arg[3] ? $arg[3] : 0666 , $arg[1] ;
262 DoTie_($tieHASH, @arg) ;
267 tie_hash_or_array(@_) ;
272 tie_hash_or_array(@_) ;
280 my $status = $self->seq($key, $value, R_FIRST());
283 while ($status == 0) {
285 $status = $self->seq($key, $value, R_NEXT());
287 foreach $key (reverse @keys) {
288 my $s = $self->del($key);
298 my $current_length = $self->length() ;
300 if ($length < $current_length) {
302 for ($key = $current_length - 1 ; $key >= $length ; -- $key)
305 elsif ($length > $current_length) {
306 $self->put($length-1, "") ;
312 croak "Usage: \$db->find_dup(key,value)\n"
316 my ($origkey, $value_wanted) = @_ ;
317 my ($key, $value) = ($origkey, 0);
320 for ($status = $db->seq($key, $value, R_CURSOR() ) ;
322 $status = $db->seq($key, $value, R_NEXT() ) ) {
324 return 0 if $key eq $origkey and $value eq $value_wanted ;
332 croak "Usage: \$db->del_dup(key,value)\n"
336 my ($key, $value) = @_ ;
337 my ($status) = $db->find_dup($key, $value) ;
338 return $status if $status != 0 ;
340 $status = $db->del($key, R_CURSOR() ) ;
346 croak "Usage: \$db->get_dup(key [,flag])\n"
347 unless @_ == 2 or @_ == 3 ;
354 my $wantarray = wantarray ;
360 # iterate through the database until either EOF ($status == 0)
361 # or a different key is encountered ($key ne $origkey).
362 for ($status = $db->seq($key, $value, R_CURSOR()) ;
363 $status == 0 and $key eq $origkey ;
364 $status = $db->seq($key, $value, R_NEXT()) ) {
366 # save the value or count number of matches
369 { ++ $values{$value} }
371 { push (@values, $value) }
378 return ($wantarray ? ($flag ? %values : @values) : $counter) ;
387 DB_File - Perl5 access to Berkeley DB version 1.x
393 [$X =] tie %hash, 'DB_File', [$filename, $flags, $mode, $DB_HASH] ;
394 [$X =] tie %hash, 'DB_File', $filename, $flags, $mode, $DB_BTREE ;
395 [$X =] tie @array, 'DB_File', $filename, $flags, $mode, $DB_RECNO ;
397 $status = $X->del($key [, $flags]) ;
398 $status = $X->put($key, $value [, $flags]) ;
399 $status = $X->get($key, $value [, $flags]) ;
400 $status = $X->seq($key, $value, $flags) ;
401 $status = $X->sync([$flags]) ;
405 $count = $X->get_dup($key) ;
406 @list = $X->get_dup($key) ;
407 %list = $X->get_dup($key, 1) ;
408 $status = $X->find_dup($key, $value) ;
409 $status = $X->del_dup($key, $value) ;
419 $old_filter = $db->filter_store_key ( sub { ... } ) ;
420 $old_filter = $db->filter_store_value( sub { ... } ) ;
421 $old_filter = $db->filter_fetch_key ( sub { ... } ) ;
422 $old_filter = $db->filter_fetch_value( sub { ... } ) ;
429 B<DB_File> is a module which allows Perl programs to make use of the
430 facilities provided by Berkeley DB version 1.x (if you have a newer
431 version of DB, see L<Using DB_File with Berkeley DB version 2 or 3>).
432 It is assumed that you have a copy of the Berkeley DB manual pages at
433 hand when reading this documentation. The interface defined here
434 mirrors the Berkeley DB interface closely.
436 Berkeley DB is a C library which provides a consistent interface to a
437 number of database formats. B<DB_File> provides an interface to all
438 three of the database types currently supported by Berkeley DB.
446 This database type allows arbitrary key/value pairs to be stored in data
447 files. This is equivalent to the functionality provided by other
448 hashing packages like DBM, NDBM, ODBM, GDBM, and SDBM. Remember though,
449 the files created using DB_HASH are not compatible with any of the
450 other packages mentioned.
452 A default hashing algorithm, which will be adequate for most
453 applications, is built into Berkeley DB. If you do need to use your own
454 hashing algorithm it is possible to write your own in Perl and have
455 B<DB_File> use it instead.
459 The btree format allows arbitrary key/value pairs to be stored in a
460 sorted, balanced binary tree.
462 As with the DB_HASH format, it is possible to provide a user defined
463 Perl routine to perform the comparison of keys. By default, though, the
464 keys are stored in lexical order.
468 DB_RECNO allows both fixed-length and variable-length flat text files
469 to be manipulated using the same key/value pair interface as in DB_HASH
470 and DB_BTREE. In this case the key will consist of a record (line)
475 =head2 Using DB_File with Berkeley DB version 2 or 3
477 Although B<DB_File> is intended to be used with Berkeley DB version 1,
478 it can also be used with version 2.or 3 In this case the interface is
479 limited to the functionality provided by Berkeley DB 1.x. Anywhere the
480 version 2 or 3 interface differs, B<DB_File> arranges for it to work
481 like version 1. This feature allows B<DB_File> scripts that were built
482 with version 1 to be migrated to version 2 or 3 without any changes.
484 If you want to make use of the new features available in Berkeley DB
485 2.x or greater, use the Perl module B<BerkeleyDB> instead.
487 B<Note:> The database file format has changed in both Berkeley DB
488 version 2 and 3. If you cannot recreate your databases, you must dump
489 any existing databases with the C<db_dump185> utility that comes with
491 Once you have rebuilt DB_File to use Berkeley DB version 2 or 3, your
492 databases can be recreated using C<db_load>. Refer to the Berkeley DB
493 documentation for further details.
495 Please read L<"COPYRIGHT"> before using version 2.x or 3.x of Berkeley
498 =head2 Interface to Berkeley DB
500 B<DB_File> allows access to Berkeley DB files using the tie() mechanism
501 in Perl 5 (for full details, see L<perlfunc/tie()>). This facility
502 allows B<DB_File> to access Berkeley DB files using either an
503 associative array (for DB_HASH & DB_BTREE file types) or an ordinary
504 array (for the DB_RECNO file type).
506 In addition to the tie() interface, it is also possible to access most
507 of the functions provided in the Berkeley DB API directly.
508 See L<THE API INTERFACE>.
510 =head2 Opening a Berkeley DB Database File
512 Berkeley DB uses the function dbopen() to open or create a database.
513 Here is the C prototype for dbopen():
516 dbopen (const char * file, int flags, int mode,
517 DBTYPE type, const void * openinfo)
519 The parameter C<type> is an enumeration which specifies which of the 3
520 interface methods (DB_HASH, DB_BTREE or DB_RECNO) is to be used.
521 Depending on which of these is actually chosen, the final parameter,
522 I<openinfo> points to a data structure which allows tailoring of the
523 specific interface method.
525 This interface is handled slightly differently in B<DB_File>. Here is
526 an equivalent call using B<DB_File>:
528 tie %array, 'DB_File', $filename, $flags, $mode, $DB_HASH ;
530 The C<filename>, C<flags> and C<mode> parameters are the direct
531 equivalent of their dbopen() counterparts. The final parameter $DB_HASH
532 performs the function of both the C<type> and C<openinfo> parameters in
535 In the example above $DB_HASH is actually a pre-defined reference to a
536 hash object. B<DB_File> has three of these pre-defined references.
537 Apart from $DB_HASH, there is also $DB_BTREE and $DB_RECNO.
539 The keys allowed in each of these pre-defined references is limited to
540 the names used in the equivalent C structure. So, for example, the
541 $DB_HASH reference will only allow keys called C<bsize>, C<cachesize>,
542 C<ffactor>, C<hash>, C<lorder> and C<nelem>.
544 To change one of these elements, just assign to it like this:
546 $DB_HASH->{'cachesize'} = 10000 ;
548 The three predefined variables $DB_HASH, $DB_BTREE and $DB_RECNO are
549 usually adequate for most applications. If you do need to create extra
550 instances of these objects, constructors are available for each file
553 Here are examples of the constructors and the valid options available
554 for DB_HASH, DB_BTREE and DB_RECNO respectively.
556 $a = new DB_File::HASHINFO ;
564 $b = new DB_File::BTREEINFO ;
574 $c = new DB_File::RECNOINFO ;
583 The values stored in the hashes above are mostly the direct equivalent
584 of their C counterpart. Like their C counterparts, all are set to a
585 default values - that means you don't have to set I<all> of the
586 values when you only want to change one. Here is an example:
588 $a = new DB_File::HASHINFO ;
589 $a->{'cachesize'} = 12345 ;
590 tie %y, 'DB_File', "filename", $flags, 0777, $a ;
592 A few of the options need extra discussion here. When used, the C
593 equivalent of the keys C<hash>, C<compare> and C<prefix> store pointers
594 to C functions. In B<DB_File> these keys are used to store references
595 to Perl subs. Below are templates for each of the subs:
601 # return the hash value for $data
607 my ($key, $key2) = @_ ;
609 # return 0 if $key1 eq $key2
610 # -1 if $key1 lt $key2
611 # 1 if $key1 gt $key2
612 return (-1 , 0 or 1) ;
617 my ($key, $key2) = @_ ;
619 # return number of bytes of $key2 which are
620 # necessary to determine that it is greater than $key1
624 See L<Changing the BTREE sort order> for an example of using the
627 If you are using the DB_RECNO interface and you intend making use of
628 C<bval>, you should check out L<The 'bval' Option>.
630 =head2 Default Parameters
632 It is possible to omit some or all of the final 4 parameters in the
633 call to C<tie> and let them take default values. As DB_HASH is the most
634 common file format used, the call:
636 tie %A, "DB_File", "filename" ;
640 tie %A, "DB_File", "filename", O_CREAT|O_RDWR, 0666, $DB_HASH ;
642 It is also possible to omit the filename parameter as well, so the
649 tie %A, "DB_File", undef, O_CREAT|O_RDWR, 0666, $DB_HASH ;
651 See L<In Memory Databases> for a discussion on the use of C<undef>
652 in place of a filename.
654 =head2 In Memory Databases
656 Berkeley DB allows the creation of in-memory databases by using NULL
657 (that is, a C<(char *)0> in C) in place of the filename. B<DB_File>
658 uses C<undef> instead of NULL to provide this functionality.
662 The DB_HASH file format is probably the most commonly used of the three
663 file formats that B<DB_File> supports. It is also very straightforward
666 =head2 A Simple Example
668 This example shows how to create a database, add key/value pairs to the
669 database, delete keys/value pairs and finally how to enumerate the
670 contents of the database.
675 use vars qw( %h $k $v ) ;
678 tie %h, "DB_File", "fruit", O_RDWR|O_CREAT, 0640, $DB_HASH
679 or die "Cannot open file 'fruit': $!\n";
681 # Add a few key/value pairs to the file
682 $h{"apple"} = "red" ;
683 $h{"orange"} = "orange" ;
684 $h{"banana"} = "yellow" ;
685 $h{"tomato"} = "red" ;
687 # Check for existence of a key
688 print "Banana Exists\n\n" if $h{"banana"} ;
690 # Delete a key/value pair.
693 # print the contents of the file
694 while (($k, $v) = each %h)
695 { print "$k -> $v\n" }
707 Note that the like ordinary associative arrays, the order of the keys
708 retrieved is in an apparently random order.
712 The DB_BTREE format is useful when you want to store data in a given
713 order. By default the keys will be stored in lexical order, but as you
714 will see from the example shown in the next section, it is very easy to
715 define your own sorting function.
717 =head2 Changing the BTREE sort order
719 This script shows how to override the default sorting algorithm that
720 BTREE uses. Instead of using the normal lexical ordering, a case
721 insensitive compare function will be used.
731 my ($key1, $key2) = @_ ;
732 "\L$key1" cmp "\L$key2" ;
735 # specify the Perl sub that will do the comparison
736 $DB_BTREE->{'compare'} = \&Compare ;
739 tie %h, "DB_File", "tree", O_RDWR|O_CREAT, 0640, $DB_BTREE
740 or die "Cannot open file 'tree': $!\n" ;
742 # Add a key/value pair to the file
743 $h{'Wall'} = 'Larry' ;
744 $h{'Smith'} = 'John' ;
745 $h{'mouse'} = 'mickey' ;
746 $h{'duck'} = 'donald' ;
751 # Cycle through the keys printing them in order.
752 # Note it is not necessary to sort the keys as
753 # the btree will have kept them in order automatically.
759 Here is the output from the code above.
765 There are a few point to bear in mind if you want to change the
766 ordering in a BTREE database:
772 The new compare function must be specified when you create the database.
776 You cannot change the ordering once the database has been created. Thus
777 you must use the same compare function every time you access the
782 =head2 Handling Duplicate Keys
784 The BTREE file type optionally allows a single key to be associated
785 with an arbitrary number of values. This option is enabled by setting
786 the flags element of C<$DB_BTREE> to R_DUP when creating the database.
788 There are some difficulties in using the tied hash interface if you
789 want to manipulate a BTREE database with duplicate keys. Consider this
796 use vars qw($filename %h ) ;
801 # Enable duplicate records
802 $DB_BTREE->{'flags'} = R_DUP ;
804 tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
805 or die "Cannot open $filename: $!\n";
807 # Add some key/value pairs to the file
808 $h{'Wall'} = 'Larry' ;
809 $h{'Wall'} = 'Brick' ; # Note the duplicate key
810 $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
811 $h{'Smith'} = 'John' ;
812 $h{'mouse'} = 'mickey' ;
814 # iterate through the associative array
815 # and print each key/value pair.
816 foreach (sort keys %h)
817 { print "$_ -> $h{$_}\n" }
829 As you can see 3 records have been successfully created with key C<Wall>
830 - the only thing is, when they are retrieved from the database they
831 I<seem> to have the same value, namely C<Larry>. The problem is caused
832 by the way that the associative array interface works. Basically, when
833 the associative array interface is used to fetch the value associated
834 with a given key, it will only ever retrieve the first value.
836 Although it may not be immediately obvious from the code above, the
837 associative array interface can be used to write values with duplicate
838 keys, but it cannot be used to read them back from the database.
840 The way to get around this problem is to use the Berkeley DB API method
841 called C<seq>. This method allows sequential access to key/value
842 pairs. See L<THE API INTERFACE> for details of both the C<seq> method
843 and the API in general.
845 Here is the script above rewritten using the C<seq> API method.
851 use vars qw($filename $x %h $status $key $value) ;
856 # Enable duplicate records
857 $DB_BTREE->{'flags'} = R_DUP ;
859 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
860 or die "Cannot open $filename: $!\n";
862 # Add some key/value pairs to the file
863 $h{'Wall'} = 'Larry' ;
864 $h{'Wall'} = 'Brick' ; # Note the duplicate key
865 $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
866 $h{'Smith'} = 'John' ;
867 $h{'mouse'} = 'mickey' ;
869 # iterate through the btree using seq
870 # and print each key/value pair.
872 for ($status = $x->seq($key, $value, R_FIRST) ;
874 $status = $x->seq($key, $value, R_NEXT) )
875 { print "$key -> $value\n" }
888 This time we have got all the key/value pairs, including the multiple
889 values associated with the key C<Wall>.
891 To make life easier when dealing with duplicate keys, B<DB_File> comes with
892 a few utility methods.
894 =head2 The get_dup() Method
896 The C<get_dup> method assists in
897 reading duplicate values from BTREE databases. The method can take the
900 $count = $x->get_dup($key) ;
901 @list = $x->get_dup($key) ;
902 %list = $x->get_dup($key, 1) ;
904 In a scalar context the method returns the number of values associated
905 with the key, C<$key>.
907 In list context, it returns all the values which match C<$key>. Note
908 that the values will be returned in an apparently random order.
910 In list context, if the second parameter is present and evaluates
911 TRUE, the method returns an associative array. The keys of the
912 associative array correspond to the values that matched in the BTREE
913 and the values of the array are a count of the number of times that
914 particular value occurred in the BTREE.
916 So assuming the database created above, we can use C<get_dup> like
923 use vars qw($filename $x %h ) ;
927 # Enable duplicate records
928 $DB_BTREE->{'flags'} = R_DUP ;
930 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
931 or die "Cannot open $filename: $!\n";
933 my $cnt = $x->get_dup("Wall") ;
934 print "Wall occurred $cnt times\n" ;
936 my %hash = $x->get_dup("Wall", 1) ;
937 print "Larry is there\n" if $hash{'Larry'} ;
938 print "There are $hash{'Brick'} Brick Walls\n" ;
940 my @list = sort $x->get_dup("Wall") ;
941 print "Wall => [@list]\n" ;
943 @list = $x->get_dup("Smith") ;
944 print "Smith => [@list]\n" ;
946 @list = $x->get_dup("Dog") ;
947 print "Dog => [@list]\n" ;
952 Wall occurred 3 times
954 There are 2 Brick Walls
955 Wall => [Brick Brick Larry]
959 =head2 The find_dup() Method
961 $status = $X->find_dup($key, $value) ;
963 This method checks for the existence of a specific key/value pair. If the
964 pair exists, the cursor is left pointing to the pair and the method
965 returns 0. Otherwise the method returns a non-zero value.
967 Assuming the database from the previous example:
973 use vars qw($filename $x %h $found) ;
975 my $filename = "tree" ;
977 # Enable duplicate records
978 $DB_BTREE->{'flags'} = R_DUP ;
980 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
981 or die "Cannot open $filename: $!\n";
983 $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
984 print "Larry Wall is $found there\n" ;
986 $found = ( $x->find_dup("Wall", "Harry") == 0 ? "" : "not") ;
987 print "Harry Wall is $found there\n" ;
995 Harry Wall is not there
998 =head2 The del_dup() Method
1000 $status = $X->del_dup($key, $value) ;
1002 This method deletes a specific key/value pair. It returns
1003 0 if they exist and have been deleted successfully.
1004 Otherwise the method returns a non-zero value.
1006 Again assuming the existence of the C<tree> database
1012 use vars qw($filename $x %h $found) ;
1014 my $filename = "tree" ;
1016 # Enable duplicate records
1017 $DB_BTREE->{'flags'} = R_DUP ;
1019 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
1020 or die "Cannot open $filename: $!\n";
1022 $x->del_dup("Wall", "Larry") ;
1024 $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
1025 print "Larry Wall is $found there\n" ;
1032 Larry Wall is not there
1034 =head2 Matching Partial Keys
1036 The BTREE interface has a feature which allows partial keys to be
1037 matched. This functionality is I<only> available when the C<seq> method
1038 is used along with the R_CURSOR flag.
1040 $x->seq($key, $value, R_CURSOR) ;
1042 Here is the relevant quote from the dbopen man page where it defines
1043 the use of the R_CURSOR flag with seq:
1045 Note, for the DB_BTREE access method, the returned key is not
1046 necessarily an exact match for the specified key. The returned key
1047 is the smallest key greater than or equal to the specified key,
1048 permitting partial key matches and range searches.
1050 In the example script below, the C<match> sub uses this feature to find
1051 and print the first matching key/value pair given a partial key.
1058 use vars qw($filename $x %h $st $key $value) ;
1064 my $orig_key = $key ;
1065 $x->seq($key, $value, R_CURSOR) ;
1066 print "$orig_key\t-> $key\t-> $value\n" ;
1069 $filename = "tree" ;
1072 $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
1073 or die "Cannot open $filename: $!\n";
1075 # Add some key/value pairs to the file
1076 $h{'mouse'} = 'mickey' ;
1077 $h{'Wall'} = 'Larry' ;
1078 $h{'Walls'} = 'Brick' ;
1079 $h{'Smith'} = 'John' ;
1083 print "IN ORDER\n" ;
1084 for ($st = $x->seq($key, $value, R_FIRST) ;
1086 $st = $x->seq($key, $value, R_NEXT) )
1088 { print "$key -> $value\n" }
1090 print "\nPARTIAL MATCH\n" ;
1110 a -> mouse -> mickey
1114 DB_RECNO provides an interface to flat text files. Both variable and
1115 fixed length records are supported.
1117 In order to make RECNO more compatible with Perl, the array offset for
1118 all RECNO arrays begins at 0 rather than 1 as in Berkeley DB.
1120 As with normal Perl arrays, a RECNO array can be accessed using
1121 negative indexes. The index -1 refers to the last element of the array,
1122 -2 the second last, and so on. Attempting to access an element before
1123 the start of the array will raise a fatal run-time error.
1125 =head2 The 'bval' Option
1127 The operation of the bval option warrants some discussion. Here is the
1128 definition of bval from the Berkeley DB 1.85 recno manual page:
1130 The delimiting byte to be used to mark the end of a
1131 record for variable-length records, and the pad charac-
1132 ter for fixed-length records. If no value is speci-
1133 fied, newlines (``\n'') are used to mark the end of
1134 variable-length records and fixed-length records are
1137 The second sentence is wrong. In actual fact bval will only default to
1138 C<"\n"> when the openinfo parameter in dbopen is NULL. If a non-NULL
1139 openinfo parameter is used at all, the value that happens to be in bval
1140 will be used. That means you always have to specify bval when making
1141 use of any of the options in the openinfo parameter. This documentation
1142 error will be fixed in the next release of Berkeley DB.
1144 That clarifies the situation with regards Berkeley DB itself. What
1145 about B<DB_File>? Well, the behavior defined in the quote above is
1146 quite useful, so B<DB_File> conforms to it.
1148 That means that you can specify other options (e.g. cachesize) and
1149 still have bval default to C<"\n"> for variable length records, and
1150 space for fixed length records.
1152 =head2 A Simple Example
1154 Here is a simple example that uses RECNO (if you are using a version
1155 of Perl earlier than 5.004_57 this example won't work -- see
1156 L<Extra RECNO Methods> for a workaround).
1162 my $filename = "text" ;
1166 tie @h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_RECNO
1167 or die "Cannot open file 'text': $!\n" ;
1169 # Add a few key/value pairs to the file
1174 push @h, "green", "black" ;
1176 my $elements = scalar @h ;
1177 print "The array contains $elements entries\n" ;
1180 print "popped $last\n" ;
1182 unshift @h, "white" ;
1183 my $first = shift @h ;
1184 print "shifted $first\n" ;
1186 # Check for existence of a key
1187 print "Element 1 Exists with value $h[1]\n" if $h[1] ;
1189 # use a negative index
1190 print "The last element is $h[-1]\n" ;
1191 print "The 2nd last element is $h[-2]\n" ;
1195 Here is the output from the script:
1197 The array contains 5 entries
1200 Element 1 Exists with value blue
1201 The last element is green
1202 The 2nd last element is yellow
1204 =head2 Extra RECNO Methods
1206 If you are using a version of Perl earlier than 5.004_57, the tied
1207 array interface is quite limited. In the example script above
1208 C<push>, C<pop>, C<shift>, C<unshift>
1209 or determining the array length will not work with a tied array.
1211 To make the interface more useful for older versions of Perl, a number
1212 of methods are supplied with B<DB_File> to simulate the missing array
1213 operations. All these methods are accessed via the object returned from
1216 Here are the methods:
1220 =item B<$X-E<gt>push(list) ;>
1222 Pushes the elements of C<list> to the end of the array.
1224 =item B<$value = $X-E<gt>pop ;>
1226 Removes and returns the last element of the array.
1228 =item B<$X-E<gt>shift>
1230 Removes and returns the first element of the array.
1232 =item B<$X-E<gt>unshift(list) ;>
1234 Pushes the elements of C<list> to the start of the array.
1236 =item B<$X-E<gt>length>
1238 Returns the number of elements in the array.
1242 =head2 Another Example
1244 Here is a more complete example that makes use of some of the methods
1245 described above. It also makes use of the API interface directly (see
1246 L<THE API INTERFACE>).
1250 use vars qw(@h $H $file $i) ;
1258 $H = tie @h, "DB_File", $file, O_RDWR|O_CREAT, 0640, $DB_RECNO
1259 or die "Cannot open file $file: $!\n" ;
1261 # first create a text file to play with
1269 # Print the records in order.
1271 # The length method is needed here because evaluating a tied
1272 # array in a scalar context does not return the number of
1273 # elements in the array.
1275 print "\nORIGINAL\n" ;
1276 foreach $i (0 .. $H->length - 1) {
1277 print "$i: $h[$i]\n" ;
1280 # use the push & pop methods
1283 print "\nThe last record was [$a]\n" ;
1285 # and the shift & unshift methods
1287 $H->unshift("first") ;
1288 print "The first record was [$a]\n" ;
1290 # Use the API to add a new record after record 2.
1292 $H->put($i, "Newbie", R_IAFTER) ;
1294 # and a new record before record 1.
1296 $H->put($i, "New One", R_IBEFORE) ;
1301 # now print the records in reverse order
1302 print "\nREVERSE\n" ;
1303 for ($i = $H->length - 1 ; $i >= 0 ; -- $i)
1304 { print "$i: $h[$i]\n" }
1306 # same again, but use the API functions instead
1307 print "\nREVERSE again\n" ;
1308 my ($s, $k, $v) = (0, 0, 0) ;
1309 for ($s = $H->seq($k, $v, R_LAST) ;
1311 $s = $H->seq($k, $v, R_PREV))
1312 { print "$k: $v\n" }
1317 and this is what it outputs:
1326 The last record was [four]
1327 The first record was [zero]
1351 Rather than iterating through the array, C<@h> like this:
1355 it is necessary to use either this:
1357 foreach $i (0 .. $H->length - 1)
1361 for ($a = $H->get($k, $v, R_FIRST) ;
1363 $a = $H->get($k, $v, R_NEXT) )
1367 Notice that both times the C<put> method was used the record index was
1368 specified using a variable, C<$i>, rather than the literal value
1369 itself. This is because C<put> will return the record number of the
1370 inserted line via that parameter.
1374 =head1 THE API INTERFACE
1376 As well as accessing Berkeley DB using a tied hash or array, it is also
1377 possible to make direct use of most of the API functions defined in the
1378 Berkeley DB documentation.
1380 To do this you need to store a copy of the object returned from the tie.
1382 $db = tie %hash, "DB_File", "filename" ;
1384 Once you have done that, you can access the Berkeley DB API functions
1385 as B<DB_File> methods directly like this:
1387 $db->put($key, $value, R_NOOVERWRITE) ;
1389 B<Important:> If you have saved a copy of the object returned from
1390 C<tie>, the underlying database file will I<not> be closed until both
1391 the tied variable is untied and all copies of the saved object are
1395 $db = tie %hash, "DB_File", "filename"
1396 or die "Cannot tie filename: $!" ;
1401 See L<The untie() Gotcha> for more details.
1403 All the functions defined in L<dbopen> are available except for
1404 close() and dbopen() itself. The B<DB_File> method interface to the
1405 supported functions have been implemented to mirror the way Berkeley DB
1406 works whenever possible. In particular note that:
1412 The methods return a status value. All return 0 on success.
1413 All return -1 to signify an error and set C<$!> to the exact
1414 error code. The return code 1 generally (but not always) means that the
1415 key specified did not exist in the database.
1417 Other return codes are defined. See below and in the Berkeley DB
1418 documentation for details. The Berkeley DB documentation should be used
1419 as the definitive source.
1423 Whenever a Berkeley DB function returns data via one of its parameters,
1424 the equivalent B<DB_File> method does exactly the same.
1428 If you are careful, it is possible to mix API calls with the tied
1429 hash/array interface in the same piece of code. Although only a few of
1430 the methods used to implement the tied interface currently make use of
1431 the cursor, you should always assume that the cursor has been changed
1432 any time the tied hash/array interface is used. As an example, this
1433 code will probably not do what you expect:
1435 $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
1436 or die "Cannot tie $filename: $!" ;
1438 # Get the first key/value pair and set the cursor
1439 $X->seq($key, $value, R_FIRST) ;
1441 # this line will modify the cursor
1442 $count = scalar keys %x ;
1444 # Get the second key/value pair.
1445 # oops, it didn't, it got the last key/value pair!
1446 $X->seq($key, $value, R_NEXT) ;
1448 The code above can be rearranged to get around the problem, like this:
1450 $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
1451 or die "Cannot tie $filename: $!" ;
1453 # this line will modify the cursor
1454 $count = scalar keys %x ;
1456 # Get the first key/value pair and set the cursor
1457 $X->seq($key, $value, R_FIRST) ;
1459 # Get the second key/value pair.
1461 $X->seq($key, $value, R_NEXT) ;
1465 All the constants defined in L<dbopen> for use in the flags parameters
1466 in the methods defined below are also available. Refer to the Berkeley
1467 DB documentation for the precise meaning of the flags values.
1469 Below is a list of the methods available.
1473 =item B<$status = $X-E<gt>get($key, $value [, $flags]) ;>
1475 Given a key (C<$key>) this method reads the value associated with it
1476 from the database. The value read from the database is returned in the
1477 C<$value> parameter.
1479 If the key does not exist the method returns 1.
1481 No flags are currently defined for this method.
1483 =item B<$status = $X-E<gt>put($key, $value [, $flags]) ;>
1485 Stores the key/value pair in the database.
1487 If you use either the R_IAFTER or R_IBEFORE flags, the C<$key> parameter
1488 will have the record number of the inserted key/value pair set.
1490 Valid flags are R_CURSOR, R_IAFTER, R_IBEFORE, R_NOOVERWRITE and
1493 =item B<$status = $X-E<gt>del($key [, $flags]) ;>
1495 Removes all key/value pairs with key C<$key> from the database.
1497 A return code of 1 means that the requested key was not in the
1500 R_CURSOR is the only valid flag at present.
1502 =item B<$status = $X-E<gt>fd ;>
1504 Returns the file descriptor for the underlying database.
1506 See L<Locking: The Trouble with fd> for an explanation for why you should
1507 not use C<fd> to lock your database.
1509 =item B<$status = $X-E<gt>seq($key, $value, $flags) ;>
1511 This interface allows sequential retrieval from the database. See
1512 L<dbopen> for full details.
1514 Both the C<$key> and C<$value> parameters will be set to the key/value
1515 pair read from the database.
1517 The flags parameter is mandatory. The valid flag values are R_CURSOR,
1518 R_FIRST, R_LAST, R_NEXT and R_PREV.
1520 =item B<$status = $X-E<gt>sync([$flags]) ;>
1522 Flushes any cached buffers to disk.
1524 R_RECNOSYNC is the only valid flag at present.
1530 A DBM Filter is a piece of code that is be used when you I<always>
1531 want to make the same transformation to all keys and/or values in a
1534 There are four methods associated with DBM Filters. All work identically,
1535 and each is used to install (or uninstall) a single DBM Filter. Each
1536 expects a single parameter, namely a reference to a sub. The only
1537 difference between them is the place that the filter is installed.
1543 =item B<filter_store_key>
1545 If a filter has been installed with this method, it will be invoked
1546 every time you write a key to a DBM database.
1548 =item B<filter_store_value>
1550 If a filter has been installed with this method, it will be invoked
1551 every time you write a value to a DBM database.
1554 =item B<filter_fetch_key>
1556 If a filter has been installed with this method, it will be invoked
1557 every time you read a key from a DBM database.
1559 =item B<filter_fetch_value>
1561 If a filter has been installed with this method, it will be invoked
1562 every time you read a value from a DBM database.
1566 You can use any combination of the methods, from none, to all four.
1568 All filter methods return the existing filter, if present, or C<undef>
1571 To delete a filter pass C<undef> to it.
1575 When each filter is called by Perl, a local copy of C<$_> will contain
1576 the key or value to be filtered. Filtering is achieved by modifying
1577 the contents of C<$_>. The return code from the filter is ignored.
1579 =head2 An Example -- the NULL termination problem.
1581 Consider the following scenario. You have a DBM database
1582 that you need to share with a third-party C application. The C application
1583 assumes that I<all> keys and values are NULL terminated. Unfortunately
1584 when Perl writes to DBM databases it doesn't use NULL termination, so
1585 your Perl application will have to manage NULL termination itself. When
1586 you write to the database you will have to use something like this:
1588 $hash{"$key\0"} = "$value\0" ;
1590 Similarly the NULL needs to be taken into account when you are considering
1591 the length of existing keys/values.
1593 It would be much better if you could ignore the NULL terminations issue
1594 in the main application code and have a mechanism that automatically
1595 added the terminating NULL to all keys and values whenever you write to
1596 the database and have them removed when you read from the database. As I'm
1597 sure you have already guessed, this is a problem that DBM Filters can
1605 my $filename = "/tmp/filt" ;
1608 my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
1609 or die "Cannot open $filename: $!\n" ;
1611 # Install DBM Filters
1612 $db->filter_fetch_key ( sub { s/\0$// } ) ;
1613 $db->filter_store_key ( sub { $_ .= "\0" } ) ;
1614 $db->filter_fetch_value( sub { s/\0$// } ) ;
1615 $db->filter_store_value( sub { $_ .= "\0" } ) ;
1617 $hash{"abc"} = "def" ;
1618 my $a = $hash{"ABC"} ;
1623 Hopefully the contents of each of the filters should be
1624 self-explanatory. Both "fetch" filters remove the terminating NULL,
1625 and both "store" filters add a terminating NULL.
1628 =head2 Another Example -- Key is a C int.
1630 Here is another real-life example. By default, whenever Perl writes to
1631 a DBM database it always writes the key and value as strings. So when
1634 $hash{12345} = "soemthing" ;
1636 the key 12345 will get stored in the DBM database as the 5 byte string
1637 "12345". If you actually want the key to be stored in the DBM database
1638 as a C int, you will have to use C<pack> when writing, and C<unpack>
1641 Here is a DBM Filter that does it:
1647 my $filename = "/tmp/filt" ;
1651 my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
1652 or die "Cannot open $filename: $!\n" ;
1654 $db->filter_fetch_key ( sub { $_ = unpack("i", $_) } ) ;
1655 $db->filter_store_key ( sub { $_ = pack ("i", $_) } ) ;
1656 $hash{123} = "def" ;
1661 This time only two filters have been used -- we only need to manipulate
1662 the contents of the key, so it wasn't necessary to install any value
1665 =head1 HINTS AND TIPS
1668 =head2 Locking: The Trouble with fd
1670 Until version 1.72 of this module, the recommended technique for locking
1671 B<DB_File> databases was to flock the filehandle returned from the "fd"
1672 function. Unfortunately this technique has been shown to be fundamentally
1673 flawed (Kudos to David Harris for tracking this down). Use it at your own
1676 The locking technique went like this.
1678 $db = tie(%db, 'DB_File', '/tmp/foo.db', O_CREAT|O_RDWR, 0644)
1679 || die "dbcreat /tmp/foo.db $!";
1681 open(DB_FH, "+<&=$fd") || die "dup $!";
1682 flock (DB_FH, LOCK_EX) || die "flock: $!";
1684 $db{"Tom"} = "Jerry" ;
1686 flock(DB_FH, LOCK_UN);
1691 In simple terms, this is what happens:
1697 Use "tie" to open the database.
1701 Lock the database with fd & flock.
1705 Read & Write to the database.
1709 Unlock and close the database.
1713 Here is the crux of the problem. A side-effect of opening the B<DB_File>
1714 database in step 2 is that an initial block from the database will get
1715 read from disk and cached in memory.
1717 To see why this is a problem, consider what can happen when two processes,
1718 say "A" and "B", both want to update the same B<DB_File> database
1719 using the locking steps outlined above. Assume process "A" has already
1720 opened the database and has a write lock, but it hasn't actually updated
1721 the database yet (it has finished step 2, but not started step 3 yet). Now
1722 process "B" tries to open the same database - step 1 will succeed,
1723 but it will block on step 2 until process "A" releases the lock. The
1724 important thing to notice here is that at this point in time both
1725 processes will have cached identical initial blocks from the database.
1727 Now process "A" updates the database and happens to change some of the
1728 data held in the initial buffer. Process "A" terminates, flushing
1729 all cached data to disk and releasing the database lock. At this point
1730 the database on disk will correctly reflect the changes made by process
1733 With the lock released, process "B" can now continue. It also updates the
1734 database and unfortunately it too modifies the data that was in its
1735 initial buffer. Once that data gets flushed to disk it will overwrite
1736 some/all of the changes process "A" made to the database.
1738 The result of this scenario is at best a database that doesn't contain
1739 what you expect. At worst the database will corrupt.
1741 The above won't happen every time competing process update the same
1742 B<DB_File> database, but it does illustrate why the technique should
1745 =head2 Safe ways to lock a database
1747 Starting with version 2.x, Berkeley DB has internal support for locking.
1748 The companion module to this one, B<BerkeleyDB>, provides an interface
1749 to this locking functionality. If you are serious about locking
1750 Berkeley DB databases, I strongly recommend using B<BerkeleyDB>.
1752 If using B<BerkeleyDB> isn't an option, there are a number of modules
1753 available on CPAN that can be used to implement locking. Each one
1754 implements locking differently and has different goals in mind. It is
1755 therefore worth knowing the difference, so that you can pick the right
1756 one for your application. Here are the three locking wrappers:
1760 =item B<Tie::DB_Lock>
1762 A B<DB_File> wrapper which creates copies of the database file for
1763 read access, so that you have a kind of a multiversioning concurrent read
1764 system. However, updates are still serial. Use for databases where reads
1765 may be lengthy and consistency problems may occur.
1767 =item B<Tie::DB_LockFile>
1769 A B<DB_File> wrapper that has the ability to lock and unlock the database
1770 while it is being used. Avoids the tie-before-flock problem by simply
1771 re-tie-ing the database when you get or drop a lock. Because of the
1772 flexibility in dropping and re-acquiring the lock in the middle of a
1773 session, this can be massaged into a system that will work with long
1774 updates and/or reads if the application follows the hints in the POD
1777 =item B<DB_File::Lock>
1779 An extremely lightweight B<DB_File> wrapper that simply flocks a lockfile
1780 before tie-ing the database and drops the lock after the untie. Allows
1781 one to use the same lockfile for multiple databases to avoid deadlock
1782 problems, if desired. Use for databases where updates are reads are
1783 quick and simple flock locking semantics are enough.
1787 =head2 Sharing Databases With C Applications
1789 There is no technical reason why a Berkeley DB database cannot be
1790 shared by both a Perl and a C application.
1792 The vast majority of problems that are reported in this area boil down
1793 to the fact that C strings are NULL terminated, whilst Perl strings are
1794 not. See L<DBM FILTERS> for a generic way to work around this problem.
1796 Here is a real example. Netscape 2.0 keeps a record of the locations you
1797 visit along with the time you last visited them in a DB_HASH database.
1798 This is usually stored in the file F<~/.netscape/history.db>. The key
1799 field in the database is the location string and the value field is the
1800 time the location was last visited stored as a 4 byte binary value.
1802 If you haven't already guessed, the location string is stored with a
1803 terminating NULL. This means you need to be careful when accessing the
1806 Here is a snippet of code that is loosely based on Tom Christiansen's
1807 I<ggh> script (available from your nearest CPAN archive in
1808 F<authors/id/TOMC/scripts/nshist.gz>).
1815 use vars qw( $dotdir $HISTORY %hist_db $href $binary_time $date ) ;
1816 $dotdir = $ENV{HOME} || $ENV{LOGNAME};
1818 $HISTORY = "$dotdir/.netscape/history.db";
1820 tie %hist_db, 'DB_File', $HISTORY
1821 or die "Cannot open $HISTORY: $!\n" ;;
1823 # Dump the complete database
1824 while ( ($href, $binary_time) = each %hist_db ) {
1826 # remove the terminating NULL
1827 $href =~ s/\x00$// ;
1829 # convert the binary time into a user friendly string
1830 $date = localtime unpack("V", $binary_time);
1831 print "$date $href\n" ;
1834 # check for the existence of a specific key
1835 # remember to add the NULL
1836 if ( $binary_time = $hist_db{"http://mox.perl.com/\x00"} ) {
1837 $date = localtime unpack("V", $binary_time) ;
1838 print "Last visited mox.perl.com on $date\n" ;
1841 print "Never visited mox.perl.com\n"
1846 =head2 The untie() Gotcha
1848 If you make use of the Berkeley DB API, it is I<very> strongly
1849 recommended that you read L<perltie/The untie Gotcha>.
1851 Even if you don't currently make use of the API interface, it is still
1854 Here is an example which illustrates the problem from a B<DB_File>
1863 $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_TRUNC
1864 or die "Cannot tie first time: $!" ;
1870 tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
1871 or die "Cannot tie second time: $!" ;
1875 When run, the script will produce this error message:
1877 Cannot tie second time: Invalid argument at bad.file line 14.
1879 Although the error message above refers to the second tie() statement
1880 in the script, the source of the problem is really with the untie()
1881 statement that precedes it.
1883 Having read L<perltie> you will probably have already guessed that the
1884 error is caused by the extra copy of the tied object stored in C<$X>.
1885 If you haven't, then the problem boils down to the fact that the
1886 B<DB_File> destructor, DESTROY, will not be called until I<all>
1887 references to the tied object are destroyed. Both the tied variable,
1888 C<%x>, and C<$X> above hold a reference to the object. The call to
1889 untie() will destroy the first, but C<$X> still holds a valid
1890 reference, so the destructor will not get called and the database file
1891 F<tst.fil> will remain open. The fact that Berkeley DB then reports the
1892 attempt to open a database that is already open via the catch-all
1893 "Invalid argument" doesn't help.
1895 If you run the script with the C<-w> flag the error message becomes:
1897 untie attempted while 1 inner references still exist at bad.file line 12.
1898 Cannot tie second time: Invalid argument at bad.file line 14.
1900 which pinpoints the real problem. Finally the script can now be
1901 modified to fix the original problem by destroying the API object
1910 $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
1914 =head1 COMMON QUESTIONS
1916 =head2 Why is there Perl source in my database?
1918 If you look at the contents of a database file created by DB_File,
1919 there can sometimes be part of a Perl script included in it.
1921 This happens because Berkeley DB uses dynamic memory to allocate
1922 buffers which will subsequently be written to the database file. Being
1923 dynamic, the memory could have been used for anything before DB
1924 malloced it. As Berkeley DB doesn't clear the memory once it has been
1925 allocated, the unused portions will contain random junk. In the case
1926 where a Perl script gets written to the database, the random junk will
1927 correspond to an area of dynamic memory that happened to be used during
1928 the compilation of the script.
1930 Unless you don't like the possibility of there being part of your Perl
1931 scripts embedded in a database file, this is nothing to worry about.
1933 =head2 How do I store complex data structures with DB_File?
1935 Although B<DB_File> cannot do this directly, there is a module which
1936 can layer transparently over B<DB_File> to accomplish this feat.
1938 Check out the MLDBM module, available on CPAN in the directory
1939 F<modules/by-module/MLDBM>.
1941 =head2 What does "Invalid Argument" mean?
1943 You will get this error message when one of the parameters in the
1944 C<tie> call is wrong. Unfortunately there are quite a few parameters to
1945 get wrong, so it can be difficult to figure out which one it is.
1947 Here are a couple of possibilities:
1953 Attempting to reopen a database without closing it.
1957 Using the O_WRONLY flag.
1961 =head2 What does "Bareword 'DB_File' not allowed" mean?
1963 You will encounter this particular error message when you have the
1964 C<strict 'subs'> pragma (or the full strict pragma) in your script.
1965 Consider this script:
1971 tie %x, DB_File, "filename" ;
1973 Running it produces the error in question:
1975 Bareword "DB_File" not allowed while "strict subs" in use
1977 To get around the error, place the word C<DB_File> in either single or
1978 double quotes, like this:
1980 tie %x, "DB_File", "filename" ;
1982 Although it might seem like a real pain, it is really worth the effort
1983 of having a C<use strict> in all your scripts.
1987 Articles that are either about B<DB_File> or make use of it.
1993 I<Full-Text Searching in Perl>, Tim Kientzle (tkientzle@ddj.com),
1994 Dr. Dobb's Journal, Issue 295, January 1999, pp 34-41
2000 Moved to the Changes file.
2004 Some older versions of Berkeley DB had problems with fixed length
2005 records using the RECNO file format. This problem has been fixed since
2006 version 1.85 of Berkeley DB.
2008 I am sure there are bugs in the code. If you do find any, or can
2009 suggest any enhancements, I would welcome your comments.
2013 B<DB_File> comes with the standard Perl source distribution. Look in
2014 the directory F<ext/DB_File>. Given the amount of time between releases
2015 of Perl the version that ships with Perl is quite likely to be out of
2016 date, so the most recent version can always be found on CPAN (see
2017 L<perlmod/CPAN> for details), in the directory
2018 F<modules/by-module/DB_File>.
2020 This version of B<DB_File> will work with either version 1.x, 2.x or
2021 3.x of Berkeley DB, but is limited to the functionality provided by
2024 The official web site for Berkeley DB is F<http://www.sleepycat.com>.
2025 All versions of Berkeley DB are available there.
2027 Alternatively, Berkeley DB version 1 is available at your nearest CPAN
2028 archive in F<src/misc/db.1.85.tar.gz>.
2030 If you are running IRIX, then get Berkeley DB version 1 from
2031 F<http://reality.sgi.com/ariel>. It has the patches necessary to
2032 compile properly on IRIX 5.3.
2036 Copyright (c) 1995-1999 Paul Marquess. All rights reserved. This program
2037 is free software; you can redistribute it and/or modify it under the
2038 same terms as Perl itself.
2040 Although B<DB_File> is covered by the Perl license, the library it
2041 makes use of, namely Berkeley DB, is not. Berkeley DB has its own
2042 copyright and its own license. Please take the time to read it.
2044 Here are are few words taken from the Berkeley DB FAQ (at
2045 F<http://www.sleepycat.com>) regarding the license:
2047 Do I have to license DB to use it in Perl scripts?
2049 No. The Berkeley DB license requires that software that uses
2050 Berkeley DB be freely redistributable. In the case of Perl, that
2051 software is Perl, and not your scripts. Any Perl scripts that you
2052 write are your property, including scripts that make use of
2053 Berkeley DB. Neither the Perl license nor the Berkeley DB license
2054 place any restriction on what you may do with them.
2056 If you are in any doubt about the license situation, contact either the
2057 Berkeley DB authors or the author of DB_File. See L<"AUTHOR"> for details.
2062 L<perl(1)>, L<dbopen(3)>, L<hash(3)>, L<recno(3)>, L<btree(3)>,
2067 The DB_File interface was written by Paul Marquess
2068 E<lt>Paul.Marquess@btinternet.comE<gt>.
2069 Questions about the DB system itself may be addressed to
2070 E<lt>db@sleepycat.com<gt>.