# DB_File.pm -- Perl 5 interface to Berkeley DB
#
-# written by Paul Marquess (pmarquess@bfsec.bt.co.uk)
-# last modified 14th November 1995
-# version 1.01
+# written by Paul Marquess (Paul.Marquess@btinternet.com)
+# last modified 22nd July 1999
+# version 1.68
+#
+# Copyright (c) 1995-1999 Paul Marquess. All rights reserved.
+# This program is free software; you can redistribute it and/or
+# modify it under the same terms as Perl itself.
+
package DB_File::HASHINFO ;
+
+require 5.003 ;
+
+use strict;
use Carp;
+require Tie::Hash;
+@DB_File::HASHINFO::ISA = qw(Tie::Hash);
+
+sub new
+{
+ my $pkg = shift ;
+ my %x ;
+ tie %x, $pkg ;
+ bless \%x, $pkg ;
+}
+
sub TIEHASH
{
- bless {} ;
+ my $pkg = shift ;
+
+ bless { VALID => { map {$_, 1}
+ qw( bsize ffactor nelem cachesize hash lorder)
+ },
+ GOT => {}
+ }, $pkg ;
}
-%elements = ( 'bsize' => 0,
- 'ffactor' => 0,
- 'nelem' => 0,
- 'cachesize' => 0,
- 'hash' => 0,
- 'lorder' => 0
- ) ;
sub FETCH
{
- return $_[0]{$_[1]} if defined $elements{$_[1]} ;
+ my $self = shift ;
+ my $key = shift ;
- croak "DB_File::HASHINFO::FETCH - Unknown element '$_[1]'" ;
+ return $self->{GOT}{$key} if exists $self->{VALID}{$key} ;
+
+ my $pkg = ref $self ;
+ croak "${pkg}::FETCH - Unknown element '$key'" ;
}
sub STORE
{
- if ( defined $elements{$_[1]} )
+ my $self = shift ;
+ my $key = shift ;
+ my $value = shift ;
+
+ if ( exists $self->{VALID}{$key} )
{
- $_[0]{$_[1]} = $_[2] ;
+ $self->{GOT}{$key} = $value ;
return ;
}
- croak "DB_File::HASHINFO::STORE - Unknown element '$_[1]'" ;
+ my $pkg = ref $self ;
+ croak "${pkg}::STORE - Unknown element '$key'" ;
}
sub DELETE
{
- if ( defined $elements{$_[1]} )
+ my $self = shift ;
+ my $key = shift ;
+
+ if ( exists $self->{VALID}{$key} )
{
- delete ${$_[0]}{$_[1]} ;
+ delete $self->{GOT}{$key} ;
return ;
}
- croak "DB_File::HASHINFO::DELETE - Unknown element '$_[1]'" ;
+ my $pkg = ref $self ;
+ croak "DB_File::HASHINFO::DELETE - Unknown element '$key'" ;
}
-
-sub DESTROY {undef %{$_[0]} }
-sub FIRSTKEY { croak "DB_File::HASHINFO::FIRSTKEY is not implemented" }
-sub NEXTKEY { croak "DB_File::HASHINFO::NEXTKEY is not implemented" }
-sub EXISTS { croak "DB_File::HASHINFO::EXISTS is not implemented" }
-sub CLEAR { croak "DB_File::HASHINFO::CLEAR is not implemented" }
-
-package DB_File::BTREEINFO ;
-use Carp;
-
-sub TIEHASH
+sub EXISTS
{
- bless {} ;
-}
-
-%elements = ( 'flags' => 0,
- 'cachesize' => 0,
- 'maxkeypage' => 0,
- 'minkeypage' => 0,
- 'psize' => 0,
- 'compare' => 0,
- 'prefix' => 0,
- 'lorder' => 0
- ) ;
+ my $self = shift ;
+ my $key = shift ;
-sub FETCH
-{
- return $_[0]{$_[1]} if defined $elements{$_[1]} ;
-
- croak "DB_File::BTREEINFO::FETCH - Unknown element '$_[1]'" ;
+ exists $self->{VALID}{$key} ;
}
-
-sub STORE
+sub NotHere
{
- if ( defined $elements{$_[1]} )
- {
- $_[0]{$_[1]} = $_[2] ;
- return ;
- }
-
- croak "DB_File::BTREEINFO::STORE - Unknown element '$_[1]'" ;
-}
+ my $self = shift ;
+ my $method = shift ;
-sub DELETE
-{
- if ( defined $elements{$_[1]} )
- {
- delete ${$_[0]}{$_[1]} ;
- return ;
- }
-
- croak "DB_File::BTREEINFO::DELETE - Unknown element '$_[1]'" ;
+ croak ref($self) . " does not define the method ${method}" ;
}
-
-sub DESTROY {undef %{$_[0]} }
-sub FIRSTKEY { croak "DB_File::BTREEINFO::FIRSTKEY is not implemented" }
-sub NEXTKEY { croak "DB_File::BTREEINFO::NEXTKEY is not implemented" }
-sub EXISTS { croak "DB_File::BTREEINFO::EXISTS is not implemented" }
-sub CLEAR { croak "DB_File::BTREEINFO::CLEAR is not implemented" }
+sub FIRSTKEY { my $self = shift ; $self->NotHere("FIRSTKEY") }
+sub NEXTKEY { my $self = shift ; $self->NotHere("NEXTKEY") }
+sub CLEAR { my $self = shift ; $self->NotHere("CLEAR") }
package DB_File::RECNOINFO ;
-use Carp;
+
+use strict ;
+
+@DB_File::RECNOINFO::ISA = qw(DB_File::HASHINFO) ;
sub TIEHASH
{
- bless {} ;
-}
-
-%elements = ( 'bval' => 0,
- 'cachesize' => 0,
- 'psize' => 0,
- 'flags' => 0,
- 'lorder' => 0,
- 'reclen' => 0,
- 'bfname' => 0
- ) ;
-sub FETCH
-{
- return $_[0]{$_[1]} if defined $elements{$_[1]} ;
+ my $pkg = shift ;
- croak "DB_File::RECNOINFO::FETCH - Unknown element '$_[1]'" ;
+ bless { VALID => { map {$_, 1}
+ qw( bval cachesize psize flags lorder reclen bfname )
+ },
+ GOT => {},
+ }, $pkg ;
}
+package DB_File::BTREEINFO ;
-sub STORE
-{
- if ( defined $elements{$_[1]} )
- {
- $_[0]{$_[1]} = $_[2] ;
- return ;
- }
-
- croak "DB_File::RECNOINFO::STORE - Unknown element '$_[1]'" ;
-}
+use strict ;
-sub DELETE
+@DB_File::BTREEINFO::ISA = qw(DB_File::HASHINFO) ;
+
+sub TIEHASH
{
- if ( defined $elements{$_[1]} )
- {
- delete ${$_[0]}{$_[1]} ;
- return ;
- }
-
- croak "DB_File::RECNOINFO::DELETE - Unknown element '$_[1]'" ;
+ my $pkg = shift ;
+
+ bless { VALID => { map {$_, 1}
+ qw( flags cachesize maxkeypage minkeypage psize
+ compare prefix lorder )
+ },
+ GOT => {},
+ }, $pkg ;
}
-sub DESTROY {undef %{$_[0]} }
-sub FIRSTKEY { croak "DB_File::RECNOINFO::FIRSTKEY is not implemented" }
-sub NEXTKEY { croak "DB_File::RECNOINFO::NEXTKEY is not implemented" }
-sub EXISTS { croak "DB_File::BTREEINFO::EXISTS is not implemented" }
-sub CLEAR { croak "DB_File::BTREEINFO::CLEAR is not implemented" }
-
-
-
package DB_File ;
+
+use strict;
+use vars qw($VERSION @ISA @EXPORT $AUTOLOAD $DB_BTREE $DB_HASH $DB_RECNO $db_version) ;
use Carp;
-$VERSION = $VERSION = 1.01 ;
+
+$VERSION = "1.68" ;
#typedef enum { DB_BTREE, DB_HASH, DB_RECNO } DBTYPE;
-$DB_BTREE = $DB_BTREE = TIEHASH DB_File::BTREEINFO ;
-$DB_HASH = $DB_HASH = TIEHASH DB_File::HASHINFO ;
-$DB_RECNO = $DB_RECNO = TIEHASH DB_File::RECNOINFO ;
+$DB_BTREE = new DB_File::BTREEINFO ;
+$DB_HASH = new DB_File::HASHINFO ;
+$DB_RECNO = new DB_File::RECNOINFO ;
-require TieHash;
+require Tie::Hash;
require Exporter;
use AutoLoader;
require DynaLoader;
-@ISA = qw(TieHash Exporter DynaLoader);
+@ISA = qw(Tie::Hash Exporter DynaLoader);
@EXPORT = qw(
$DB_BTREE $DB_HASH $DB_RECNO
+
BTREEMAGIC
BTREEVERSION
DB_LOCK
R_SETCURSOR
R_SNAPSHOT
__R_UNUSED
+
);
sub AUTOLOAD {
- local($constname);
+ my($constname);
($constname = $AUTOLOAD) =~ s/.*:://;
- $val = constant($constname, @_ ? $_[0] : 0);
+ my $val = constant($constname, @_ ? $_[0] : 0);
if ($! != 0) {
- if ($! =~ /Invalid/) {
+ if ($! =~ /Invalid/ || $!{EINVAL}) {
$AutoLoader::AUTOLOAD = $AUTOLOAD;
goto &AutoLoader::AUTOLOAD;
}
else {
- ($pack,$file,$line) = caller;
+ my($pack,$file,$line) = caller;
croak "Your vendor has not defined DB macro $constname, used at $file line $line.
";
}
goto &$AUTOLOAD;
}
-bootstrap DB_File ;
+
+eval {
+ # Make all Fcntl O_XXX constants available for importing
+ require Fcntl;
+ my @O = grep /^O_/, @Fcntl::EXPORT;
+ Fcntl->import(@O); # first we import what we want to export
+ push(@EXPORT, @O);
+};
+
+## import borrowed from IO::File
+## exports Fcntl constants if available.
+#sub import {
+# my $pkg = shift;
+# my $callpkg = caller;
+# Exporter::export $pkg, $callpkg, @_;
+# eval {
+# require Fcntl;
+# Exporter::export 'Fcntl', $callpkg, '/^O_/';
+# };
+#}
+
+bootstrap DB_File $VERSION;
# Preloaded methods go here. Autoload methods go after __END__, and are
# processed by the autosplit program.
+sub tie_hash_or_array
+{
+ my (@arg) = @_ ;
+ my $tieHASH = ( (caller(1))[3] =~ /TIEHASH/ ) ;
+
+ $arg[4] = tied %{ $arg[4] }
+ if @arg >= 5 && ref $arg[4] && $arg[4] =~ /=HASH/ && tied %{ $arg[4] } ;
+
+ # make recno in Berkeley DB version 2 work like recno in version 1.
+ if ($db_version > 1 and defined $arg[4] and $arg[4] =~ /RECNO/ and
+ $arg[1] and ! -e $arg[1]) {
+ open(FH, ">$arg[1]") or return undef ;
+ close FH ;
+ chmod $arg[3] ? $arg[3] : 0666 , $arg[1] ;
+ }
+
+ DoTie_($tieHASH, @arg) ;
+}
+
+sub TIEHASH
+{
+ tie_hash_or_array(@_) ;
+}
+
+sub TIEARRAY
+{
+ tie_hash_or_array(@_) ;
+}
+
+sub CLEAR
+{
+ my $self = shift;
+ my $key = "" ;
+ my $value = "" ;
+ my $status = $self->seq($key, $value, R_FIRST());
+ my @keys;
+
+ while ($status == 0) {
+ push @keys, $key;
+ $status = $self->seq($key, $value, R_NEXT());
+ }
+ foreach $key (reverse @keys) {
+ my $s = $self->del($key);
+ }
+}
+
+sub EXTEND { }
+
+sub STORESIZE
+{
+ my $self = shift;
+ my $length = shift ;
+ my $current_length = $self->length() ;
+
+ if ($length < $current_length) {
+ my $key ;
+ for ($key = $current_length - 1 ; $key >= $length ; -- $key)
+ { $self->del($key) }
+ }
+ elsif ($length > $current_length) {
+ $self->put($length-1, "") ;
+ }
+}
+
+sub find_dup
+{
+ croak "Usage: \$db->find_dup(key,value)\n"
+ unless @_ == 3 ;
+
+ my $db = shift ;
+ my ($origkey, $value_wanted) = @_ ;
+ my ($key, $value) = ($origkey, 0);
+ my ($status) = 0 ;
+
+ for ($status = $db->seq($key, $value, R_CURSOR() ) ;
+ $status == 0 ;
+ $status = $db->seq($key, $value, R_NEXT() ) ) {
+
+ return 0 if $key eq $origkey and $value eq $value_wanted ;
+ }
+
+ return $status ;
+}
+
+sub del_dup
+{
+ croak "Usage: \$db->del_dup(key,value)\n"
+ unless @_ == 3 ;
+
+ my $db = shift ;
+ my ($key, $value) = @_ ;
+ my ($status) = $db->find_dup($key, $value) ;
+ return $status if $status != 0 ;
+
+ $status = $db->del($key, R_CURSOR() ) ;
+ return $status ;
+}
+
+sub get_dup
+{
+ croak "Usage: \$db->get_dup(key [,flag])\n"
+ unless @_ == 2 or @_ == 3 ;
+
+ my $db = shift ;
+ my $key = shift ;
+ my $flag = shift ;
+ my $value = 0 ;
+ my $origkey = $key ;
+ my $wantarray = wantarray ;
+ my %values = () ;
+ my @values = () ;
+ my $counter = 0 ;
+ my $status = 0 ;
+
+ # iterate through the database until either EOF ($status == 0)
+ # or a different key is encountered ($key ne $origkey).
+ for ($status = $db->seq($key, $value, R_CURSOR()) ;
+ $status == 0 and $key eq $origkey ;
+ $status = $db->seq($key, $value, R_NEXT()) ) {
+
+ # save the value or count number of matches
+ if ($wantarray) {
+ if ($flag)
+ { ++ $values{$value} }
+ else
+ { push (@values, $value) }
+ }
+ else
+ { ++ $counter }
+
+ }
+
+ return ($wantarray ? ($flag ? %values : @values) : $counter) ;
+}
+
+
1;
__END__
-=cut
-
=head1 NAME
-DB_File - Perl5 access to Berkeley DB
+DB_File - Perl5 access to Berkeley DB version 1.x
=head1 SYNOPSIS
use DB_File ;
-
- [$X =] tie %hash, DB_File, $filename [, $flags, $mode, $DB_HASH] ;
- [$X =] tie %hash, DB_File, $filename, $flags, $mode, $DB_BTREE ;
- [$X =] tie @array, DB_File, $filename, $flags, $mode, $DB_RECNO ;
-
+
+ [$X =] tie %hash, 'DB_File', [$filename, $flags, $mode, $DB_HASH] ;
+ [$X =] tie %hash, 'DB_File', $filename, $flags, $mode, $DB_BTREE ;
+ [$X =] tie @array, 'DB_File', $filename, $flags, $mode, $DB_RECNO ;
+
$status = $X->del($key [, $flags]) ;
$status = $X->put($key, $value [, $flags]) ;
$status = $X->get($key, $value [, $flags]) ;
- $status = $X->seq($key, $value [, $flags]) ;
+ $status = $X->seq($key, $value, $flags) ;
$status = $X->sync([$flags]) ;
$status = $X->fd ;
-
+
+ # BTREE only
+ $count = $X->get_dup($key) ;
+ @list = $X->get_dup($key) ;
+ %list = $X->get_dup($key, 1) ;
+ $status = $X->find_dup($key, $value) ;
+ $status = $X->del_dup($key, $value) ;
+
+ # RECNO only
+ $a = $X->length;
+ $a = $X->pop ;
+ $X->push(list);
+ $a = $X->shift;
+ $X->unshift(list);
+
+ # DBM Filters
+ $old_filter = $db->filter_store_key ( sub { ... } ) ;
+ $old_filter = $db->filter_store_value( sub { ... } ) ;
+ $old_filter = $db->filter_fetch_key ( sub { ... } ) ;
+ $old_filter = $db->filter_fetch_value( sub { ... } ) ;
+
untie %hash ;
untie @array ;
=head1 DESCRIPTION
B<DB_File> is a module which allows Perl programs to make use of the
-facilities provided by Berkeley DB. If you intend to use this
-module you should really have a copy of the Berkeley DB manualpage at
-hand. The interface defined here mirrors the Berkeley DB interface
-closely.
+facilities provided by Berkeley DB version 1.x (if you have a newer
+version of DB, see L<Using DB_File with Berkeley DB version 2>). It is
+assumed that you have a copy of the Berkeley DB manual pages at hand
+when reading this documentation. The interface defined here mirrors the
+Berkeley DB interface closely.
Berkeley DB is a C library which provides a consistent interface to a
number of database formats. B<DB_File> provides an interface to all
=over 5
-=item DB_HASH
+=item B<DB_HASH>
-This database type allows arbitrary key/data pairs to be stored in data
+This database type allows arbitrary key/value pairs to be stored in data
files. This is equivalent to the functionality provided by other
hashing packages like DBM, NDBM, ODBM, GDBM, and SDBM. Remember though,
the files created using DB_HASH are not compatible with any of the
hashing algorithm it is possible to write your own in Perl and have
B<DB_File> use it instead.
-=item DB_BTREE
+=item B<DB_BTREE>
-The btree format allows arbitrary key/data pairs to be stored in a
+The btree format allows arbitrary key/value pairs to be stored in a
sorted, balanced binary tree.
As with the DB_HASH format, it is possible to provide a user defined
Perl routine to perform the comparison of keys. By default, though, the
keys are stored in lexical order.
-=item DB_RECNO
+=item B<DB_RECNO>
DB_RECNO allows both fixed-length and variable-length flat text files
to be manipulated using the same key/value pair interface as in DB_HASH
=back
-=head2 How does DB_File interface to Berkeley DB?
+=head2 Using DB_File with Berkeley DB version 2
+
+Although B<DB_File> is intended to be used with Berkeley DB version 1,
+it can also be used with version 2. In this case the interface is
+limited to the functionality provided by Berkeley DB 1.x. Anywhere the
+version 2 interface differs, B<DB_File> arranges for it to work like
+version 1. This feature allows B<DB_File> scripts that were built with
+version 1 to be migrated to version 2 without any changes.
+
+If you want to make use of the new features available in Berkeley DB
+2.x, use the Perl module B<BerkeleyDB> instead.
+
+At the time of writing this document the B<BerkeleyDB> module is still
+alpha quality (the version number is < 1.0), and so unsuitable for use
+in any serious development work. Once its version number is >= 1.0, it
+is considered stable enough for real work.
+
+B<Note:> The database file format has changed in Berkeley DB version 2.
+If you cannot recreate your databases, you must dump any existing
+databases with the C<db_dump185> utility that comes with Berkeley DB.
+Once you have rebuilt DB_File to use Berkeley DB version 2, your
+databases can be recreated using C<db_load>. Refer to the Berkeley DB
+documentation for further details.
+
+Please read L<"COPYRIGHT"> before using version 2.x of Berkeley DB with
+DB_File.
+
+=head2 Interface to Berkeley DB
B<DB_File> allows access to Berkeley DB files using the tie() mechanism
in Perl 5 (for full details, see L<perlfunc/tie()>). This facility
associative array (for DB_HASH & DB_BTREE file types) or an ordinary
array (for the DB_RECNO file type).
-In addition to the tie() interface, it is also possible to use most of
-the functions provided in the Berkeley DB API.
+In addition to the tie() interface, it is also possible to access most
+of the functions provided in the Berkeley DB API directly.
+See L<THE API INTERFACE>.
-=head2 Differences with Berkeley DB
+=head2 Opening a Berkeley DB Database File
Berkeley DB uses the function dbopen() to open or create a database.
-Below is the C prototype for dbopen().
+Here is the C prototype for dbopen():
DB*
dbopen (const char * file, int flags, int mode,
specific interface method.
This interface is handled slightly differently in B<DB_File>. Here is
-an equivalent call using B<DB_File>.
+an equivalent call using B<DB_File>:
- tie %array, DB_File, $filename, $flags, $mode, $DB_HASH ;
+ tie %array, 'DB_File', $filename, $flags, $mode, $DB_HASH ;
The C<filename>, C<flags> and C<mode> parameters are the direct
equivalent of their dbopen() counterparts. The final parameter $DB_HASH
performs the function of both the C<type> and C<openinfo> parameters in
dbopen().
-In the example above $DB_HASH is actually a reference to a hash
-object. B<DB_File> has three of these pre-defined references. Apart
-from $DB_HASH, there is also $DB_BTREE and $DB_RECNO.
+In the example above $DB_HASH is actually a pre-defined reference to a
+hash object. B<DB_File> has three of these pre-defined references.
+Apart from $DB_HASH, there is also $DB_BTREE and $DB_RECNO.
The keys allowed in each of these pre-defined references is limited to
the names used in the equivalent C structure. So, for example, the
$DB_HASH reference will only allow keys called C<bsize>, C<cachesize>,
-C<ffactor>, C<hash>, C<lorder> and C<nelem>.
+C<ffactor>, C<hash>, C<lorder> and C<nelem>.
+
+To change one of these elements, just assign to it like this:
+
+ $DB_HASH->{'cachesize'} = 10000 ;
+
+The three predefined variables $DB_HASH, $DB_BTREE and $DB_RECNO are
+usually adequate for most applications. If you do need to create extra
+instances of these objects, constructors are available for each file
+type.
+
+Here are examples of the constructors and the valid options available
+for DB_HASH, DB_BTREE and DB_RECNO respectively.
+
+ $a = new DB_File::HASHINFO ;
+ $a->{'bsize'} ;
+ $a->{'cachesize'} ;
+ $a->{'ffactor'};
+ $a->{'hash'} ;
+ $a->{'lorder'} ;
+ $a->{'nelem'} ;
+
+ $b = new DB_File::BTREEINFO ;
+ $b->{'flags'} ;
+ $b->{'cachesize'} ;
+ $b->{'maxkeypage'} ;
+ $b->{'minkeypage'} ;
+ $b->{'psize'} ;
+ $b->{'compare'} ;
+ $b->{'prefix'} ;
+ $b->{'lorder'} ;
+
+ $c = new DB_File::RECNOINFO ;
+ $c->{'bval'} ;
+ $c->{'cachesize'} ;
+ $c->{'psize'} ;
+ $c->{'flags'} ;
+ $c->{'lorder'} ;
+ $c->{'reclen'} ;
+ $c->{'bfname'} ;
+
+The values stored in the hashes above are mostly the direct equivalent
+of their C counterpart. Like their C counterparts, all are set to a
+default values - that means you don't have to set I<all> of the
+values when you only want to change one. Here is an example:
+
+ $a = new DB_File::HASHINFO ;
+ $a->{'cachesize'} = 12345 ;
+ tie %y, 'DB_File', "filename", $flags, 0777, $a ;
+
+A few of the options need extra discussion here. When used, the C
+equivalent of the keys C<hash>, C<compare> and C<prefix> store pointers
+to C functions. In B<DB_File> these keys are used to store references
+to Perl subs. Below are templates for each of the subs:
+
+ sub hash
+ {
+ my ($data) = @_ ;
+ ...
+ # return the hash value for $data
+ return $hash ;
+ }
-To change one of these elements, just assign to it like this
+ sub compare
+ {
+ my ($key, $key2) = @_ ;
+ ...
+ # return 0 if $key1 eq $key2
+ # -1 if $key1 lt $key2
+ # 1 if $key1 gt $key2
+ return (-1 , 0 or 1) ;
+ }
- $DB_HASH{cachesize} = 10000 ;
+ sub prefix
+ {
+ my ($key, $key2) = @_ ;
+ ...
+ # return number of bytes of $key2 which are
+ # necessary to determine that it is greater than $key1
+ return $bytes ;
+ }
+
+See L<Changing the BTREE sort order> for an example of using the
+C<compare> template.
+
+If you are using the DB_RECNO interface and you intend making use of
+C<bval>, you should check out L<The 'bval' Option>.
+
+=head2 Default Parameters
+
+It is possible to omit some or all of the final 4 parameters in the
+call to C<tie> and let them take default values. As DB_HASH is the most
+common file format used, the call:
+
+ tie %A, "DB_File", "filename" ;
+is equivalent to:
-=head2 RECNO
+ tie %A, "DB_File", "filename", O_CREAT|O_RDWR, 0666, $DB_HASH ;
+It is also possible to omit the filename parameter as well, so the
+call:
-In order to make RECNO more compatible with Perl the array offset for all
-RECNO arrays begins at 0 rather than 1 as in Berkeley DB.
+ tie %A, "DB_File" ;
+is equivalent to:
+
+ tie %A, "DB_File", undef, O_CREAT|O_RDWR, 0666, $DB_HASH ;
+
+See L<In Memory Databases> for a discussion on the use of C<undef>
+in place of a filename.
=head2 In Memory Databases
Berkeley DB allows the creation of in-memory databases by using NULL
-(that is, a C<(char *)0 in C) in place of the filename. B<DB_File>
+(that is, a C<(char *)0> in C) in place of the filename. B<DB_File>
uses C<undef> instead of NULL to provide this functionality.
+=head1 DB_HASH
+
+The DB_HASH file format is probably the most commonly used of the three
+file formats that B<DB_File> supports. It is also very straightforward
+to use.
+
+=head2 A Simple Example
+
+This example shows how to create a database, add key/value pairs to the
+database, delete keys/value pairs and finally how to enumerate the
+contents of the database.
+
+ use strict ;
+ use DB_File ;
+ use vars qw( %h $k $v ) ;
+
+ unlink "fruit" ;
+ tie %h, "DB_File", "fruit", O_RDWR|O_CREAT, 0640, $DB_HASH
+ or die "Cannot open file 'fruit': $!\n";
+
+ # Add a few key/value pairs to the file
+ $h{"apple"} = "red" ;
+ $h{"orange"} = "orange" ;
+ $h{"banana"} = "yellow" ;
+ $h{"tomato"} = "red" ;
+
+ # Check for existence of a key
+ print "Banana Exists\n\n" if $h{"banana"} ;
+
+ # Delete a key/value pair.
+ delete $h{"apple"} ;
+
+ # print the contents of the file
+ while (($k, $v) = each %h)
+ { print "$k -> $v\n" }
+
+ untie %h ;
+
+here is the output:
+
+ Banana Exists
+
+ orange -> orange
+ tomato -> red
+ banana -> yellow
+
+Note that the like ordinary associative arrays, the order of the keys
+retrieved is in an apparently random order.
+
+=head1 DB_BTREE
+
+The DB_BTREE format is useful when you want to store data in a given
+order. By default the keys will be stored in lexical order, but as you
+will see from the example shown in the next section, it is very easy to
+define your own sorting function.
+
+=head2 Changing the BTREE sort order
+
+This script shows how to override the default sorting algorithm that
+BTREE uses. Instead of using the normal lexical ordering, a case
+insensitive compare function will be used.
+
+ use strict ;
+ use DB_File ;
+
+ my %h ;
+
+ sub Compare
+ {
+ my ($key1, $key2) = @_ ;
+ "\L$key1" cmp "\L$key2" ;
+ }
+
+ # specify the Perl sub that will do the comparison
+ $DB_BTREE->{'compare'} = \&Compare ;
+
+ unlink "tree" ;
+ tie %h, "DB_File", "tree", O_RDWR|O_CREAT, 0640, $DB_BTREE
+ or die "Cannot open file 'tree': $!\n" ;
+
+ # Add a key/value pair to the file
+ $h{'Wall'} = 'Larry' ;
+ $h{'Smith'} = 'John' ;
+ $h{'mouse'} = 'mickey' ;
+ $h{'duck'} = 'donald' ;
+
+ # Delete
+ delete $h{"duck"} ;
+
+ # Cycle through the keys printing them in order.
+ # Note it is not necessary to sort the keys as
+ # the btree will have kept them in order automatically.
+ foreach (keys %h)
+ { print "$_\n" }
+
+ untie %h ;
+
+Here is the output from the code above.
+
+ mouse
+ Smith
+ Wall
+
+There are a few point to bear in mind if you want to change the
+ordering in a BTREE database:
+
+=over 5
+
+=item 1.
+
+The new compare function must be specified when you create the database.
+
+=item 2.
+
+You cannot change the ordering once the database has been created. Thus
+you must use the same compare function every time you access the
+database.
+
+=back
+
+=head2 Handling Duplicate Keys
+
+The BTREE file type optionally allows a single key to be associated
+with an arbitrary number of values. This option is enabled by setting
+the flags element of C<$DB_BTREE> to R_DUP when creating the database.
+
+There are some difficulties in using the tied hash interface if you
+want to manipulate a BTREE database with duplicate keys. Consider this
+code:
+
+ use strict ;
+ use DB_File ;
+
+ use vars qw($filename %h ) ;
+
+ $filename = "tree" ;
+ unlink $filename ;
+
+ # Enable duplicate records
+ $DB_BTREE->{'flags'} = R_DUP ;
+
+ tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
+ or die "Cannot open $filename: $!\n";
+
+ # Add some key/value pairs to the file
+ $h{'Wall'} = 'Larry' ;
+ $h{'Wall'} = 'Brick' ; # Note the duplicate key
+ $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
+ $h{'Smith'} = 'John' ;
+ $h{'mouse'} = 'mickey' ;
+
+ # iterate through the associative array
+ # and print each key/value pair.
+ foreach (sort keys %h)
+ { print "$_ -> $h{$_}\n" }
+
+ untie %h ;
+
+Here is the output:
+
+ Smith -> John
+ Wall -> Larry
+ Wall -> Larry
+ Wall -> Larry
+ mouse -> mickey
+
+As you can see 3 records have been successfully created with key C<Wall>
+- the only thing is, when they are retrieved from the database they
+I<seem> to have the same value, namely C<Larry>. The problem is caused
+by the way that the associative array interface works. Basically, when
+the associative array interface is used to fetch the value associated
+with a given key, it will only ever retrieve the first value.
+
+Although it may not be immediately obvious from the code above, the
+associative array interface can be used to write values with duplicate
+keys, but it cannot be used to read them back from the database.
+
+The way to get around this problem is to use the Berkeley DB API method
+called C<seq>. This method allows sequential access to key/value
+pairs. See L<THE API INTERFACE> for details of both the C<seq> method
+and the API in general.
+
+Here is the script above rewritten using the C<seq> API method.
+
+ use strict ;
+ use DB_File ;
+
+ use vars qw($filename $x %h $status $key $value) ;
+
+ $filename = "tree" ;
+ unlink $filename ;
+
+ # Enable duplicate records
+ $DB_BTREE->{'flags'} = R_DUP ;
+
+ $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
+ or die "Cannot open $filename: $!\n";
+
+ # Add some key/value pairs to the file
+ $h{'Wall'} = 'Larry' ;
+ $h{'Wall'} = 'Brick' ; # Note the duplicate key
+ $h{'Wall'} = 'Brick' ; # Note the duplicate key and value
+ $h{'Smith'} = 'John' ;
+ $h{'mouse'} = 'mickey' ;
+
+ # iterate through the btree using seq
+ # and print each key/value pair.
+ $key = $value = 0 ;
+ for ($status = $x->seq($key, $value, R_FIRST) ;
+ $status == 0 ;
+ $status = $x->seq($key, $value, R_NEXT) )
+ { print "$key -> $value\n" }
+
+ undef $x ;
+ untie %h ;
+
+that prints:
+
+ Smith -> John
+ Wall -> Brick
+ Wall -> Brick
+ Wall -> Larry
+ mouse -> mickey
+
+This time we have got all the key/value pairs, including the multiple
+values associated with the key C<Wall>.
+
+To make life easier when dealing with duplicate keys, B<DB_File> comes with
+a few utility methods.
+
+=head2 The get_dup() Method
+
+The C<get_dup> method assists in
+reading duplicate values from BTREE databases. The method can take the
+following forms:
+
+ $count = $x->get_dup($key) ;
+ @list = $x->get_dup($key) ;
+ %list = $x->get_dup($key, 1) ;
+
+In a scalar context the method returns the number of values associated
+with the key, C<$key>.
+
+In list context, it returns all the values which match C<$key>. Note
+that the values will be returned in an apparently random order.
+
+In list context, if the second parameter is present and evaluates
+TRUE, the method returns an associative array. The keys of the
+associative array correspond to the values that matched in the BTREE
+and the values of the array are a count of the number of times that
+particular value occurred in the BTREE.
+
+So assuming the database created above, we can use C<get_dup> like
+this:
+
+ use strict ;
+ use DB_File ;
+
+ use vars qw($filename $x %h ) ;
+
+ $filename = "tree" ;
+
+ # Enable duplicate records
+ $DB_BTREE->{'flags'} = R_DUP ;
+
+ $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
+ or die "Cannot open $filename: $!\n";
+
+ my $cnt = $x->get_dup("Wall") ;
+ print "Wall occurred $cnt times\n" ;
+
+ my %hash = $x->get_dup("Wall", 1) ;
+ print "Larry is there\n" if $hash{'Larry'} ;
+ print "There are $hash{'Brick'} Brick Walls\n" ;
+
+ my @list = sort $x->get_dup("Wall") ;
+ print "Wall => [@list]\n" ;
+
+ @list = $x->get_dup("Smith") ;
+ print "Smith => [@list]\n" ;
+
+ @list = $x->get_dup("Dog") ;
+ print "Dog => [@list]\n" ;
+
+
+and it will print:
+
+ Wall occurred 3 times
+ Larry is there
+ There are 2 Brick Walls
+ Wall => [Brick Brick Larry]
+ Smith => [John]
+ Dog => []
+
+=head2 The find_dup() Method
+
+ $status = $X->find_dup($key, $value) ;
+
+This method checks for the existance of a specific key/value pair. If the
+pair exists, the cursor is left pointing to the pair and the method
+returns 0. Otherwise the method returns a non-zero value.
+
+Assuming the database from the previous example:
+
+ use strict ;
+ use DB_File ;
+
+ use vars qw($filename $x %h $found) ;
+
+ my $filename = "tree" ;
+
+ # Enable duplicate records
+ $DB_BTREE->{'flags'} = R_DUP ;
+
+ $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
+ or die "Cannot open $filename: $!\n";
+
+ $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
+ print "Larry Wall is $found there\n" ;
+
+ $found = ( $x->find_dup("Wall", "Harry") == 0 ? "" : "not") ;
+ print "Harry Wall is $found there\n" ;
+
+ undef $x ;
+ untie %h ;
+
+prints this
+
+ Larry Wall is there
+ Harry Wall is not there
+
+
+=head2 The del_dup() Method
+
+ $status = $X->del_dup($key, $value) ;
+
+This method deletes a specific key/value pair. It returns
+0 if they exist and have been deleted successfully.
+Otherwise the method returns a non-zero value.
+
+Again assuming the existance of the C<tree> database
+
+ use strict ;
+ use DB_File ;
+
+ use vars qw($filename $x %h $found) ;
+
+ my $filename = "tree" ;
+
+ # Enable duplicate records
+ $DB_BTREE->{'flags'} = R_DUP ;
+
+ $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
+ or die "Cannot open $filename: $!\n";
+
+ $x->del_dup("Wall", "Larry") ;
+
+ $found = ( $x->find_dup("Wall", "Larry") == 0 ? "" : "not") ;
+ print "Larry Wall is $found there\n" ;
+
+ undef $x ;
+ untie %h ;
+
+prints this
+
+ Larry Wall is not there
+
+=head2 Matching Partial Keys
+
+The BTREE interface has a feature which allows partial keys to be
+matched. This functionality is I<only> available when the C<seq> method
+is used along with the R_CURSOR flag.
+
+ $x->seq($key, $value, R_CURSOR) ;
+
+Here is the relevant quote from the dbopen man page where it defines
+the use of the R_CURSOR flag with seq:
+
+ Note, for the DB_BTREE access method, the returned key is not
+ necessarily an exact match for the specified key. The returned key
+ is the smallest key greater than or equal to the specified key,
+ permitting partial key matches and range searches.
+
+In the example script below, the C<match> sub uses this feature to find
+and print the first matching key/value pair given a partial key.
+
+ use strict ;
+ use DB_File ;
+ use Fcntl ;
+
+ use vars qw($filename $x %h $st $key $value) ;
+
+ sub match
+ {
+ my $key = shift ;
+ my $value = 0;
+ my $orig_key = $key ;
+ $x->seq($key, $value, R_CURSOR) ;
+ print "$orig_key\t-> $key\t-> $value\n" ;
+ }
+
+ $filename = "tree" ;
+ unlink $filename ;
+
+ $x = tie %h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_BTREE
+ or die "Cannot open $filename: $!\n";
+
+ # Add some key/value pairs to the file
+ $h{'mouse'} = 'mickey' ;
+ $h{'Wall'} = 'Larry' ;
+ $h{'Walls'} = 'Brick' ;
+ $h{'Smith'} = 'John' ;
+
+
+ $key = $value = 0 ;
+ print "IN ORDER\n" ;
+ for ($st = $x->seq($key, $value, R_FIRST) ;
+ $st == 0 ;
+ $st = $x->seq($key, $value, R_NEXT) )
+
+ { print "$key -> $value\n" }
+
+ print "\nPARTIAL MATCH\n" ;
+
+ match "Wa" ;
+ match "A" ;
+ match "a" ;
+
+ undef $x ;
+ untie %h ;
+
+Here is the output:
+
+ IN ORDER
+ Smith -> John
+ Wall -> Larry
+ Walls -> Brick
+ mouse -> mickey
+
+ PARTIAL MATCH
+ Wa -> Wall -> Larry
+ A -> Smith -> John
+ a -> mouse -> mickey
+
+=head1 DB_RECNO
+
+DB_RECNO provides an interface to flat text files. Both variable and
+fixed length records are supported.
+
+In order to make RECNO more compatible with Perl, the array offset for
+all RECNO arrays begins at 0 rather than 1 as in Berkeley DB.
+
+As with normal Perl arrays, a RECNO array can be accessed using
+negative indexes. The index -1 refers to the last element of the array,
+-2 the second last, and so on. Attempting to access an element before
+the start of the array will raise a fatal run-time error.
+
+=head2 The 'bval' Option
+
+The operation of the bval option warrants some discussion. Here is the
+definition of bval from the Berkeley DB 1.85 recno manual page:
+
+ The delimiting byte to be used to mark the end of a
+ record for variable-length records, and the pad charac-
+ ter for fixed-length records. If no value is speci-
+ fied, newlines (``\n'') are used to mark the end of
+ variable-length records and fixed-length records are
+ padded with spaces.
+
+The second sentence is wrong. In actual fact bval will only default to
+C<"\n"> when the openinfo parameter in dbopen is NULL. If a non-NULL
+openinfo parameter is used at all, the value that happens to be in bval
+will be used. That means you always have to specify bval when making
+use of any of the options in the openinfo parameter. This documentation
+error will be fixed in the next release of Berkeley DB.
+
+That clarifies the situation with regards Berkeley DB itself. What
+about B<DB_File>? Well, the behavior defined in the quote above is
+quite useful, so B<DB_File> conforms to it.
+
+That means that you can specify other options (e.g. cachesize) and
+still have bval default to C<"\n"> for variable length records, and
+space for fixed length records.
+
+=head2 A Simple Example
-=head2 Using the Berkeley DB Interface Directly
+Here is a simple example that uses RECNO (if you are using a version
+of Perl earlier than 5.004_57 this example won't work -- see
+L<Extra RECNO Methods> for a workaround).
+
+ use strict ;
+ use DB_File ;
+
+ my $filename = "text" ;
+ unlink $filename ;
+
+ my @h ;
+ tie @h, "DB_File", $filename, O_RDWR|O_CREAT, 0640, $DB_RECNO
+ or die "Cannot open file 'text': $!\n" ;
+
+ # Add a few key/value pairs to the file
+ $h[0] = "orange" ;
+ $h[1] = "blue" ;
+ $h[2] = "yellow" ;
+
+ push @h, "green", "black" ;
+
+ my $elements = scalar @h ;
+ print "The array contains $elements entries\n" ;
+
+ my $last = pop @h ;
+ print "popped $last\n" ;
+
+ unshift @h, "white" ;
+ my $first = shift @h ;
+ print "shifted $first\n" ;
+
+ # Check for existence of a key
+ print "Element 1 Exists with value $h[1]\n" if $h[1] ;
+
+ # use a negative index
+ print "The last element is $h[-1]\n" ;
+ print "The 2nd last element is $h[-2]\n" ;
+
+ untie @h ;
+
+Here is the output from the script:
+
+ The array contains 5 entries
+ popped black
+ shifted white
+ Element 1 Exists with value blue
+ The last element is green
+ The 2nd last element is yellow
+
+=head2 Extra RECNO Methods
+
+If you are using a version of Perl earlier than 5.004_57, the tied
+array interface is quite limited. In the example script above
+C<push>, C<pop>, C<shift>, C<unshift>
+or determining the array length will not work with a tied array.
+
+To make the interface more useful for older versions of Perl, a number
+of methods are supplied with B<DB_File> to simulate the missing array
+operations. All these methods are accessed via the object returned from
+the tie call.
+
+Here are the methods:
+
+=over 5
+
+=item B<$X-E<gt>push(list) ;>
+
+Pushes the elements of C<list> to the end of the array.
+
+=item B<$value = $X-E<gt>pop ;>
+
+Removes and returns the last element of the array.
+
+=item B<$X-E<gt>shift>
+
+Removes and returns the first element of the array.
+
+=item B<$X-E<gt>unshift(list) ;>
+
+Pushes the elements of C<list> to the start of the array.
+
+=item B<$X-E<gt>length>
+
+Returns the number of elements in the array.
+
+=back
+
+=head2 Another Example
+
+Here is a more complete example that makes use of some of the methods
+described above. It also makes use of the API interface directly (see
+L<THE API INTERFACE>).
+
+ use strict ;
+ use vars qw(@h $H $file $i) ;
+ use DB_File ;
+ use Fcntl ;
+
+ $file = "text" ;
+
+ unlink $file ;
+
+ $H = tie @h, "DB_File", $file, O_RDWR|O_CREAT, 0640, $DB_RECNO
+ or die "Cannot open file $file: $!\n" ;
+
+ # first create a text file to play with
+ $h[0] = "zero" ;
+ $h[1] = "one" ;
+ $h[2] = "two" ;
+ $h[3] = "three" ;
+ $h[4] = "four" ;
+
+
+ # Print the records in order.
+ #
+ # The length method is needed here because evaluating a tied
+ # array in a scalar context does not return the number of
+ # elements in the array.
+
+ print "\nORIGINAL\n" ;
+ foreach $i (0 .. $H->length - 1) {
+ print "$i: $h[$i]\n" ;
+ }
+
+ # use the push & pop methods
+ $a = $H->pop ;
+ $H->push("last") ;
+ print "\nThe last record was [$a]\n" ;
+
+ # and the shift & unshift methods
+ $a = $H->shift ;
+ $H->unshift("first") ;
+ print "The first record was [$a]\n" ;
+
+ # Use the API to add a new record after record 2.
+ $i = 2 ;
+ $H->put($i, "Newbie", R_IAFTER) ;
+
+ # and a new record before record 1.
+ $i = 1 ;
+ $H->put($i, "New One", R_IBEFORE) ;
+
+ # delete record 3
+ $H->del(3) ;
+
+ # now print the records in reverse order
+ print "\nREVERSE\n" ;
+ for ($i = $H->length - 1 ; $i >= 0 ; -- $i)
+ { print "$i: $h[$i]\n" }
+
+ # same again, but use the API functions instead
+ print "\nREVERSE again\n" ;
+ my ($s, $k, $v) = (0, 0, 0) ;
+ for ($s = $H->seq($k, $v, R_LAST) ;
+ $s == 0 ;
+ $s = $H->seq($k, $v, R_PREV))
+ { print "$k: $v\n" }
+
+ undef $H ;
+ untie @h ;
+
+and this is what it outputs:
+
+ ORIGINAL
+ 0: zero
+ 1: one
+ 2: two
+ 3: three
+ 4: four
+
+ The last record was [four]
+ The first record was [zero]
+
+ REVERSE
+ 5: last
+ 4: three
+ 3: Newbie
+ 2: one
+ 1: New One
+ 0: first
+
+ REVERSE again
+ 5: last
+ 4: three
+ 3: Newbie
+ 2: one
+ 1: New One
+ 0: first
+
+Notes:
+
+=over 5
+
+=item 1.
+
+Rather than iterating through the array, C<@h> like this:
+
+ foreach $i (@h)
+
+it is necessary to use either this:
+
+ foreach $i (0 .. $H->length - 1)
+
+or this:
+
+ for ($a = $H->get($k, $v, R_FIRST) ;
+ $a == 0 ;
+ $a = $H->get($k, $v, R_NEXT) )
+
+=item 2.
+
+Notice that both times the C<put> method was used the record index was
+specified using a variable, C<$i>, rather than the literal value
+itself. This is because C<put> will return the record number of the
+inserted line via that parameter.
+
+=back
+
+=head1 THE API INTERFACE
As well as accessing Berkeley DB using a tied hash or array, it is also
-possible to make direct use of most of the functions defined in the
+possible to make direct use of most of the API functions defined in the
Berkeley DB documentation.
+To do this you need to store a copy of the object returned from the tie.
-To do this you need to remember the return value from the tie.
-
- $db = tie %hash, DB_File, "filename"
+ $db = tie %hash, "DB_File", "filename" ;
Once you have done that, you can access the Berkeley DB API functions
-directly.
+as B<DB_File> methods directly like this:
$db->put($key, $value, R_NOOVERWRITE) ;
-All the functions defined in L<dbx(3X)> are available except for
-close() and dbopen() itself. The B<DB_File> interface to these
-functions have been implemented to mirror the the way Berkeley DB
-works. In particular note that all the functions return only a status
-value. Whenever a Berkeley DB function returns data via one of its
-parameters, the B<DB_File> equivalent does exactly the same.
+B<Important:> If you have saved a copy of the object returned from
+C<tie>, the underlying database file will I<not> be closed until both
+the tied variable is untied and all copies of the saved object are
+destroyed.
+
+ use DB_File ;
+ $db = tie %hash, "DB_File", "filename"
+ or die "Cannot tie filename: $!" ;
+ ...
+ undef $db ;
+ untie %hash ;
+
+See L<The untie() Gotcha> for more details.
+
+All the functions defined in L<dbopen> are available except for
+close() and dbopen() itself. The B<DB_File> method interface to the
+supported functions have been implemented to mirror the way Berkeley DB
+works whenever possible. In particular note that:
+
+=over 5
+
+=item *
+
+The methods return a status value. All return 0 on success.
+All return -1 to signify an error and set C<$!> to the exact
+error code. The return code 1 generally (but not always) means that the
+key specified did not exist in the database.
+
+Other return codes are defined. See below and in the Berkeley DB
+documentation for details. The Berkeley DB documentation should be used
+as the definitive source.
+
+=item *
+
+Whenever a Berkeley DB function returns data via one of its parameters,
+the equivalent B<DB_File> method does exactly the same.
+
+=item *
+
+If you are careful, it is possible to mix API calls with the tied
+hash/array interface in the same piece of code. Although only a few of
+the methods used to implement the tied interface currently make use of
+the cursor, you should always assume that the cursor has been changed
+any time the tied hash/array interface is used. As an example, this
+code will probably not do what you expect:
+
+ $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
+ or die "Cannot tie $filename: $!" ;
+
+ # Get the first key/value pair and set the cursor
+ $X->seq($key, $value, R_FIRST) ;
+
+ # this line will modify the cursor
+ $count = scalar keys %x ;
+
+ # Get the second key/value pair.
+ # oops, it didn't, it got the last key/value pair!
+ $X->seq($key, $value, R_NEXT) ;
+
+The code above can be rearranged to get around the problem, like this:
+
+ $X = tie %x, 'DB_File', $filename, O_RDWR|O_CREAT, 0777, $DB_BTREE
+ or die "Cannot tie $filename: $!" ;
+
+ # this line will modify the cursor
+ $count = scalar keys %x ;
+
+ # Get the first key/value pair and set the cursor
+ $X->seq($key, $value, R_FIRST) ;
+
+ # Get the second key/value pair.
+ # worked this time.
+ $X->seq($key, $value, R_NEXT) ;
+
+=back
-All the constants defined in L<dbopen> are also available.
+All the constants defined in L<dbopen> for use in the flags parameters
+in the methods defined below are also available. Refer to the Berkeley
+DB documentation for the precise meaning of the flags values.
-Below is a list of the functions available.
+Below is a list of the methods available.
=over 5
-=item get
+=item B<$status = $X-E<gt>get($key, $value [, $flags]) ;>
+
+Given a key (C<$key>) this method reads the value associated with it
+from the database. The value read from the database is returned in the
+C<$value> parameter.
-Same as in C<recno> except that the flags parameter is optional.
-Remember the value associated with the key you request is returned in
-the $value parameter.
+If the key does not exist the method returns 1.
-=item put
+No flags are currently defined for this method.
-As usual the flags parameter is optional.
+=item B<$status = $X-E<gt>put($key, $value [, $flags]) ;>
-If you use either the R_IAFTER or R_IBEFORE flags, the key parameter
+Stores the key/value pair in the database.
+
+If you use either the R_IAFTER or R_IBEFORE flags, the C<$key> parameter
will have the record number of the inserted key/value pair set.
-=item del
+Valid flags are R_CURSOR, R_IAFTER, R_IBEFORE, R_NOOVERWRITE and
+R_SETCURSOR.
+
+=item B<$status = $X-E<gt>del($key [, $flags]) ;>
+
+Removes all key/value pairs with key C<$key> from the database.
+
+A return code of 1 means that the requested key was not in the
+database.
+
+R_CURSOR is the only valid flag at present.
-The flags parameter is optional.
+=item B<$status = $X-E<gt>fd ;>
-=item fd
+Returns the file descriptor for the underlying database.
-As in I<recno>.
+See L<Locking Databases> for an example of how to make use of the
+C<fd> method to lock your database.
-=item seq
+=item B<$status = $X-E<gt>seq($key, $value, $flags) ;>
-The flags parameter is optional.
+This interface allows sequential retrieval from the database. See
+L<dbopen> for full details.
-Both the key and value parameters will be set.
+Both the C<$key> and C<$value> parameters will be set to the key/value
+pair read from the database.
-=item sync
+The flags parameter is mandatory. The valid flag values are R_CURSOR,
+R_FIRST, R_LAST, R_NEXT and R_PREV.
-The flags parameter is optional.
+=item B<$status = $X-E<gt>sync([$flags]) ;>
+
+Flushes any cached buffers to disk.
+
+R_RECNOSYNC is the only valid flag at present.
=back
-=head1 EXAMPLES
+=head1 DBM FILTERS
-It is always a lot easier to understand something when you see a real
-example. So here are a few.
+A DBM Filter is a piece of code that is be used when you I<always>
+want to make the same transformation to all keys and/or values in a
+DBM database.
-=head2 Using HASH
+There are four methods associated with DBM Filters. All work identically,
+and each is used to install (or uninstall) a single DBM Filter. Each
+expects a single parameter, namely a reference to a sub. The only
+difference between them is the place that the filter is installed.
- use DB_File ;
- use Fcntl ;
-
- tie %h, "DB_File", "hashed", O_RDWR|O_CREAT, 0640, $DB_HASH ;
-
- # Add a key/value pair to the file
- $h{"apple"} = "orange" ;
-
- # Check for existence of a key
- print "Exists\n" if $h{"banana"} ;
-
- # Delete
- delete $h{"apple"} ;
-
- untie %h ;
+To summarise:
-=head2 Using BTREE
+=over 5
-Here is sample of code which used BTREE. Just to make life more
-interesting the default comparision function will not be used. Instead
-a Perl sub, C<Compare()>, will be used to do a case insensitive
-comparison.
+=item B<filter_store_key>
- use DB_File ;
- use Fcntl ;
-
- sub Compare
- {
- my ($key1, $key2) = @_ ;
-
- "\L$key1" cmp "\L$key2" ;
- }
-
- $DB_BTREE->{compare} = 'Compare' ;
-
- tie %h, 'DB_File', "tree", O_RDWR|O_CREAT, 0640, $DB_BTREE ;
-
- # Add a key/value pair to the file
- $h{'Wall'} = 'Larry' ;
- $h{'Smith'} = 'John' ;
- $h{'mouse'} = 'mickey' ;
- $h{'duck'} = 'donald' ;
-
- # Delete
- delete $h{"duck"} ;
-
- # Cycle through the keys printing them in order.
- # Note it is not necessary to sort the keys as
- # the btree will have kept them in order automatically.
- foreach (keys %h)
- { print "$_\n" }
-
- untie %h ;
+If a filter has been installed with this method, it will be invoked
+every time you write a key to a DBM database.
-Here is the output from the code above.
+=item B<filter_store_value>
- mouse
- Smith
- Wall
+If a filter has been installed with this method, it will be invoked
+every time you write a value to a DBM database.
-=head2 Using RECNO
+=item B<filter_fetch_key>
- use DB_File ;
- use Fcntl ;
-
- $DB_RECNO->{psize} = 3000 ;
-
- tie @h, DB_File, "text", O_RDWR|O_CREAT, 0640, $DB_RECNO ;
-
- # Add a key/value pair to the file
- $h[0] = "orange" ;
-
- # Check for existence of a key
- print "Exists\n" if $h[1] ;
-
- untie @h ;
+If a filter has been installed with this method, it will be invoked
+every time you read a key from a DBM database.
+
+=item B<filter_fetch_value>
+
+If a filter has been installed with this method, it will be invoked
+every time you read a value from a DBM database.
+
+=back
+
+You can use any combination of the methods, from none, to all four.
+
+All filter methods return the existing filter, if present, or C<undef>
+in not.
+
+To delete a filter pass C<undef> to it.
+
+=head2 The Filter
+
+When each filter is called by Perl, a local copy of C<$_> will contain
+the key or value to be filtered. Filtering is achieved by modifying
+the contents of C<$_>. The return code from the filter is ignored.
+
+=head2 An Example -- the NULL termination problem.
+
+Consider the following scenario. You have a DBM database
+that you need to share with a third-party C application. The C application
+assumes that I<all> keys and values are NULL terminated. Unfortunately
+when Perl writes to DBM databases it doesn't use NULL termination, so
+your Perl application will have to manage NULL termination itself. When
+you write to the database you will have to use something like this:
+
+ $hash{"$key\0"} = "$value\0" ;
+
+Similarly the NULL needs to be taken into account when you are considering
+the length of existing keys/values.
+
+It would be much better if you could ignore the NULL terminations issue
+in the main application code and have a mechanism that automatically
+added the terminating NULL to all keys and values whenever you write to
+the database and have them removed when you read from the database. As I'm
+sure you have already guessed, this is a problem that DBM Filters can
+fix very easily.
+
+ use strict ;
+ use DB_File ;
+
+ my %hash ;
+ my $filename = "/tmp/filt" ;
+ unlink $filename ;
+
+ my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
+ or die "Cannot open $filename: $!\n" ;
+
+ # Install DBM Filters
+ $db->filter_fetch_key ( sub { s/\0$// } ) ;
+ $db->filter_store_key ( sub { $_ .= "\0" } ) ;
+ $db->filter_fetch_value( sub { s/\0$// } ) ;
+ $db->filter_store_value( sub { $_ .= "\0" } ) ;
+
+ $hash{"abc"} = "def" ;
+ my $a = $hash{"ABC"} ;
+ # ...
+ undef $db ;
+ untie %hash ;
+
+Hopefully the contents of each of the filters should be
+self-explanatory. Both "fetch" filters remove the terminating NULL,
+and both "store" filters add a terminating NULL.
+
+
+=head2 Another Example -- Key is a C int.
+
+Here is another real-life example. By default, whenever Perl writes to
+a DBM database it always writes the key and value as strings. So when
+you use this:
+
+ $hash{12345} = "soemthing" ;
+
+the key 12345 will get stored in the DBM database as the 5 byte string
+"12345". If you actually want the key to be stored in the DBM database
+as a C int, you will have to use C<pack> when writing, and C<unpack>
+when reading.
+
+Here is a DBM Filter that does it:
+
+ use strict ;
+ use DB_File ;
+ my %hash ;
+ my $filename = "/tmp/filt" ;
+ unlink $filename ;
+
+
+ my $db = tie %hash, 'DB_File', $filename, O_CREAT|O_RDWR, 0666, $DB_HASH
+ or die "Cannot open $filename: $!\n" ;
+
+ $db->filter_fetch_key ( sub { $_ = unpack("i", $_) } ) ;
+ $db->filter_store_key ( sub { $_ = pack ("i", $_) } ) ;
+ $hash{123} = "def" ;
+ # ...
+ undef $db ;
+ untie %hash ;
+
+This time only two filters have been used -- we only need to manipulate
+the contents of the key, so it wasn't necessary to install any value
+filters.
+
+=head1 HINTS AND TIPS
=head2 Locking Databases
open() to give something Perl will flock() for you. Run this repeatedly
in the background to watch the locks granted in proper order.
- use Fcntl;
use DB_File;
use strict;
print "$$: Write lock granted\n";
$db{$key} = $value;
+ $db->sync; # to flush
sleep 10;
flock(DB_FH, LOCK_UN);
+ undef $db;
untie %db;
close(DB_FH);
print "$$: Updated db to $key=$value\n";
-=head1 HISTORY
+=head2 Sharing Databases With C Applications
+
+There is no technical reason why a Berkeley DB database cannot be
+shared by both a Perl and a C application.
+
+The vast majority of problems that are reported in this area boil down
+to the fact that C strings are NULL terminated, whilst Perl strings are
+not. See L<DBM FILTERS> for a generic way to work around this problem.
+
+Here is a real example. Netscape 2.0 keeps a record of the locations you
+visit along with the time you last visited them in a DB_HASH database.
+This is usually stored in the file F<~/.netscape/history.db>. The key
+field in the database is the location string and the value field is the
+time the location was last visited stored as a 4 byte binary value.
+
+If you haven't already guessed, the location string is stored with a
+terminating NULL. This means you need to be careful when accessing the
+database.
+
+Here is a snippet of code that is loosely based on Tom Christiansen's
+I<ggh> script (available from your nearest CPAN archive in
+F<authors/id/TOMC/scripts/nshist.gz>).
+
+ use strict ;
+ use DB_File ;
+ use Fcntl ;
+
+ use vars qw( $dotdir $HISTORY %hist_db $href $binary_time $date ) ;
+ $dotdir = $ENV{HOME} || $ENV{LOGNAME};
+
+ $HISTORY = "$dotdir/.netscape/history.db";
+
+ tie %hist_db, 'DB_File', $HISTORY
+ or die "Cannot open $HISTORY: $!\n" ;;
+
+ # Dump the complete database
+ while ( ($href, $binary_time) = each %hist_db ) {
+
+ # remove the terminating NULL
+ $href =~ s/\x00$// ;
+
+ # convert the binary time into a user friendly string
+ $date = localtime unpack("V", $binary_time);
+ print "$date $href\n" ;
+ }
+
+ # check for the existence of a specific key
+ # remember to add the NULL
+ if ( $binary_time = $hist_db{"http://mox.perl.com/\x00"} ) {
+ $date = localtime unpack("V", $binary_time) ;
+ print "Last visited mox.perl.com on $date\n" ;
+ }
+ else {
+ print "Never visited mox.perl.com\n"
+ }
+
+ untie %hist_db ;
+
+=head2 The untie() Gotcha
+
+If you make use of the Berkeley DB API, it is I<very> strongly
+recommended that you read L<perltie/The untie Gotcha>.
+
+Even if you don't currently make use of the API interface, it is still
+worth reading it.
+
+Here is an example which illustrates the problem from a B<DB_File>
+perspective:
-=over
+ use DB_File ;
+ use Fcntl ;
-=item 0.1
+ my %x ;
+ my $X ;
-First Release.
+ $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_TRUNC
+ or die "Cannot tie first time: $!" ;
-=item 0.2
+ $x{123} = 456 ;
-When B<DB_File> is opening a database file it no longer terminates the
-process if I<dbopen> returned an error. This allows file protection
-errors to be caught at run time. Thanks to Judith Grass
-E<lt>grass@cybercash.comE<gt> for spotting the bug.
+ untie %x ;
-=item 0.3
+ tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
+ or die "Cannot tie second time: $!" ;
-Added prototype support for multiple btree compare callbacks.
+ untie %x ;
-=item 1.0
+When run, the script will produce this error message:
-B<DB_File> has been in use for over a year. To reflect that, the
-version number has been incremented to 1.0.
+ Cannot tie second time: Invalid argument at bad.file line 14.
-Added complete support for multiple concurrent callbacks.
+Although the error message above refers to the second tie() statement
+in the script, the source of the problem is really with the untie()
+statement that precedes it.
-Using the I<push> method on an empty list didn't work properly. This
-has been fixed.
+Having read L<perltie> you will probably have already guessed that the
+error is caused by the extra copy of the tied object stored in C<$X>.
+If you haven't, then the problem boils down to the fact that the
+B<DB_File> destructor, DESTROY, will not be called until I<all>
+references to the tied object are destroyed. Both the tied variable,
+C<%x>, and C<$X> above hold a reference to the object. The call to
+untie() will destroy the first, but C<$X> still holds a valid
+reference, so the destructor will not get called and the database file
+F<tst.fil> will remain open. The fact that Berkeley DB then reports the
+attempt to open a database that is alreday open via the catch-all
+"Invalid argument" doesn't help.
-=item 1.01
+If you run the script with the C<-w> flag the error message becomes:
-Fixed a core dump problem with SunOS.
+ untie attempted while 1 inner references still exist at bad.file line 12.
+ Cannot tie second time: Invalid argument at bad.file line 14.
-The return value from TIEHASH wasn't set to NULL when dbopen returned
-an error.
+which pinpoints the real problem. Finally the script can now be
+modified to fix the original problem by destroying the API object
+before the untie:
-=head1 WARNINGS
+ ...
+ $x{123} = 456 ;
-If you happen find any other functions defined in the source for this
-module that have not been mentioned in this document -- beware. I may
-drop them at a moments notice.
+ undef $X ;
+ untie %x ;
-If you cannot find any, then either you didn't look very hard or the
-moment has passed and I have dropped them.
+ $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
+ ...
+
+
+=head1 COMMON QUESTIONS
+
+=head2 Why is there Perl source in my database?
+
+If you look at the contents of a database file created by DB_File,
+there can sometimes be part of a Perl script included in it.
+
+This happens because Berkeley DB uses dynamic memory to allocate
+buffers which will subsequently be written to the database file. Being
+dynamic, the memory could have been used for anything before DB
+malloced it. As Berkeley DB doesn't clear the memory once it has been
+allocated, the unused portions will contain random junk. In the case
+where a Perl script gets written to the database, the random junk will
+correspond to an area of dynamic memory that happened to be used during
+the compilation of the script.
+
+Unless you don't like the possibility of there being part of your Perl
+scripts embedded in a database file, this is nothing to worry about.
+
+=head2 How do I store complex data structures with DB_File?
+
+Although B<DB_File> cannot do this directly, there is a module which
+can layer transparently over B<DB_File> to accomplish this feat.
+
+Check out the MLDBM module, available on CPAN in the directory
+F<modules/by-module/MLDBM>.
+
+=head2 What does "Invalid Argument" mean?
+
+You will get this error message when one of the parameters in the
+C<tie> call is wrong. Unfortunately there are quite a few parameters to
+get wrong, so it can be difficult to figure out which one it is.
+
+Here are a couple of possibilities:
+
+=over 5
+
+=item 1.
+
+Attempting to reopen a database without closing it.
+
+=item 2.
+
+Using the O_WRONLY flag.
+
+=back
+
+=head2 What does "Bareword 'DB_File' not allowed" mean?
+
+You will encounter this particular error message when you have the
+C<strict 'subs'> pragma (or the full strict pragma) in your script.
+Consider this script:
+
+ use strict ;
+ use DB_File ;
+ use vars qw(%x) ;
+ tie %x, DB_File, "filename" ;
+
+Running it produces the error in question:
+
+ Bareword "DB_File" not allowed while "strict subs" in use
+
+To get around the error, place the word C<DB_File> in either single or
+double quotes, like this:
+
+ tie %x, "DB_File", "filename" ;
+
+Although it might seem like a real pain, it is really worth the effort
+of having a C<use strict> in all your scripts.
+
+=head1 REFERENCES
+
+Articles that are either about B<DB_File> or make use of it.
+
+=over 5
+
+=item 1.
+
+I<Full-Text Searching in Perl>, Tim Kientzle (tkientzle@ddj.com),
+Dr. Dobb's Journal, Issue 295, January 1999, pp 34-41
+
+=back
+
+=head1 HISTORY
+
+Moved to the Changes file.
=head1 BUGS
Some older versions of Berkeley DB had problems with fixed length
-records using the RECNO file format. The newest version at the time of
-writing was 1.85 - this seems to have fixed the problems with RECNO.
+records using the RECNO file format. This problem has been fixed since
+version 1.85 of Berkeley DB.
I am sure there are bugs in the code. If you do find any, or can
suggest any enhancements, I would welcome your comments.
=head1 AVAILABILITY
-Berkeley DB is available at your nearest CPAN archive (see
-L<perlmod/"CPAN"> for a list) in F<src/misc/db.1.85.tar.gz>, or via the
-host F<ftp.cs.berkeley.edu> in F</ucb/4bsd/db.tar.gz>. It is I<not> under
-the GPL.
+B<DB_File> comes with the standard Perl source distribution. Look in
+the directory F<ext/DB_File>. Given the amount of time between releases
+of Perl the version that ships with Perl is quite likely to be out of
+date, so the most recent version can always be found on CPAN (see
+L<perlmod/CPAN> for details), in the directory
+F<modules/by-module/DB_File>.
-=head1 SEE ALSO
+This version of B<DB_File> will work with either version 1.x or 2.x of
+Berkeley DB, but is limited to the functionality provided by version 1.
+
+The official web site for Berkeley DB is F<http://www.sleepycat.com>.
+Both versions 1 and 2 of Berkeley DB are available there.
+
+Alternatively, Berkeley DB version 1 is available at your nearest CPAN
+archive in F<src/misc/db.1.85.tar.gz>.
+
+If you are running IRIX, then get Berkeley DB version 1 from
+F<http://reality.sgi.com/ariel>. It has the patches necessary to
+compile properly on IRIX 5.3.
+
+=head1 COPYRIGHT
+
+Copyright (c) 1995-1999 Paul Marquess. All rights reserved. This program
+is free software; you can redistribute it and/or modify it under the
+same terms as Perl itself.
+
+Although B<DB_File> is covered by the Perl license, the library it
+makes use of, namely Berkeley DB, is not. Berkeley DB has its own
+copyright and its own license. Please take the time to read it.
-L<perl(1)>, L<dbopen(3)>, L<hash(3)>, L<recno(3)>, L<btree(3)>
+Here are are few words taken from the Berkeley DB FAQ (at
+http://www.sleepycat.com) regarding the license:
+
+ Do I have to license DB to use it in Perl scripts?
+
+ No. The Berkeley DB license requires that software that uses
+ Berkeley DB be freely redistributable. In the case of Perl, that
+ software is Perl, and not your scripts. Any Perl scripts that you
+ write are your property, including scripts that make use of
+ Berkeley DB. Neither the Perl license nor the Berkeley DB license
+ place any restriction on what you may do with them.
+
+If you are in any doubt about the license situation, contact either the
+Berkeley DB authors or the author of DB_File. See L<"AUTHOR"> for details.
+
+
+=head1 SEE ALSO
-Berkeley DB is available from F<ftp.cs.berkeley.edu> in the directory
-F</ucb/4bsd>.
+L<perl(1)>, L<dbopen(3)>, L<hash(3)>, L<recno(3)>, L<btree(3)>,
+L<dbmfilter>
=head1 AUTHOR
The DB_File interface was written by Paul Marquess
-<pmarquess@bfsec.bt.co.uk>.
-Questions about the DB system itself may be addressed to Keith Bostic
-<bostic@cs.berkeley.edu>.
+E<lt>Paul.Marquess@btinternet.comE<gt>.
+Questions about the DB system itself may be addressed to
+E<lt>db@sleepycat.com<gt>.
=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff