IRIX Base Documentation 2002 November/SGI IRIX Base Documentation 2002 November.iso/usr/share/catman/p_man/cat3/perl5/DB_File.z/DB_File

Text File | 2002-10-03 | 59.7 KB | 1,783 lines

DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



NNNNAAAAMMMMEEEE
     DB_File - Perl5 access to Berkeley DB version 1.x

SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
      use DB_File ;

      [$X =] tie %hash,  'DB_File', [$filename, $flags, $mode, $DB_HASH] ;
      [$X =] tie %hash,  'DB_File', $filename, $flags, $mode, $DB_BTREE ;
      [$X =] tie @array, 'DB_File', $filename, $flags, $mode, $DB_RECNO ;

      $status = $X->del($key [, $flags]) ;
      $status = $X->put($key, $value [, $flags]) ;
      $status = $X->get($key, $value [, $flags]) ;
      $status = $X->seq($key, $value, $flags) ;
      $status = $X->sync([$flags]) ;
      $status = $X->fd ;

      # BTREE only
      $count = $X->get_dup($key) ;
      @list  = $X->get_dup($key) ;
      %list  = $X->get_dup($key, 1) ;

      # RECNO only
      $a = $X->length;
      $a = $X->pop ;
      $X->push(list);
      $a = $X->shift;
      $X->unshift(list);

      untie %hash ;
      untie @array ;


DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     DDDDBBBB____FFFFiiiilllleeee is a module which allows Perl programs to make use of the
     facilities provided by Berkeley DB version 1.x (if you have a newer
     version of DB, see the section on _U_s_i_n_g _D_B__F_i_l_e _w_i_t_h _B_e_r_k_e_l_e_y _D_B _v_e_r_s_i_o_n
     _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.  DDDDBBBB____FFFFiiiilllleeee provides an interface to all three
     of the database types currently supported by Berkeley DB.

     The file types are:

     DDDDBBBB____HHHHAAAASSSSHHHH
          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



                                                                        PPPPaaaaggggeeee 1111






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



          with any of the other packages mentioned.

          A default hashing algorithm, which will be adequate for most
          applications, is built into Berkeley DB. If you do need to use your
          own hashing algorithm it is possible to write your own in Perl and
          have DDDDBBBB____FFFFiiiilllleeee use it instead.

     DDDDBBBB____BBBBTTTTRRRREEEEEEEE
          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.

     DDDDBBBB____RRRREEEECCCCNNNNOOOO
          DB_RECNO allows both fixed-length and variable-length flat text
          files to be manipulated using the same key/value pair interface as
          in DB_HASH and DB_BTREE.  In this case the key will consist of a
          record (line) number.

     UUUUssssiiiinnnngggg DDDDBBBB____FFFFiiiilllleeee wwwwiiiitttthhhh BBBBeeeerrrrkkkkeeeelllleeeeyyyy DDDDBBBB vvvveeeerrrrssssiiiioooonnnn 2222

     Although DDDDBBBB____FFFFiiiilllleeee 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, DDDDBBBB____FFFFiiiilllleeee arranges for it to work like version 1. This
     feature allows DDDDBBBB____FFFFiiiilllleeee 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 BBBBeeeerrrrkkkkeeeelllleeeeyyyyDDDDBBBB instead.

     At the time of writing this document the BBBBeeeerrrrkkkkeeeelllleeeeyyyyDDDDBBBB 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.

     NNNNooootttteeee:::: 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 db_dump185 utility that comes with Berkeley DB.  Once you have
     upgraded DB_File to use Berkeley DB version 2, your databases can be
     recreated using db_load. Refer to the Berkeley DB documentation for
     further details.

     Please read the _C_O_P_Y_R_I_G_H_T manpage before using version 2.x of Berkeley DB
     with DB_File.

     IIIInnnntttteeeerrrrffffaaaacccceeee ttttoooo BBBBeeeerrrrkkkkeeeelllleeeeyyyy DDDDBBBB






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DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     DDDDBBBB____FFFFiiiilllleeee allows access to Berkeley DB files using the _t_i_e() mechanism in
     Perl 5 (for full details, see the tie() entry in the _p_e_r_l_f_u_n_c manpage).
     This facility allows DDDDBBBB____FFFFiiiilllleeee to access Berkeley DB files using either an
     associative array (for DB_HASH & DB_BTREE file types) or an ordinary
     array (for the DB_RECNO file type).

     In addition to the _t_i_e() interface, it is also possible to access most of
     the functions provided in the Berkeley DB API directly.  See the section
     on _T_H_E _A_P_I _I_N_T_E_R_F_A_C_E.

     OOOOppppeeeennnniiiinnnngggg aaaa BBBBeeeerrrrkkkkeeeelllleeeeyyyy DDDDBBBB DDDDaaaattttaaaabbbbaaaasssseeee FFFFiiiilllleeee

     Berkeley DB uses the function _d_b_o_p_e_n() to open or create a database.
     Here is the C prototype for _d_b_o_p_e_n():

           DB*
           dbopen (const char * file, int flags, int mode,
                   DBTYPE type, const void * openinfo)

     The parameter type is an enumeration which specifies which of the 3
     interface methods (DB_HASH, DB_BTREE or DB_RECNO) is to be used.
     Depending on which of these is actually chosen, the final parameter,
     _o_p_e_n_i_n_f_o points to a data structure which allows tailoring of the
     specific interface method.

     This interface is handled slightly differently in DDDDBBBB____FFFFiiiilllleeee. Here is an
     equivalent call using DDDDBBBB____FFFFiiiilllleeee:

             tie %array, 'DB_File', $filename, $flags, $mode, $DB_HASH ;

     The filename, flags and mode parameters are the direct equivalent of
     their _d_b_o_p_e_n() counterparts. The final parameter $DB_HASH performs the
     function of both the type and openinfo parameters in _d_b_o_p_e_n().

     In the example above $DB_HASH is actually a pre-defined reference to a
     hash object. DDDDBBBB____FFFFiiiilllleeee 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 bsize, cachesize, ffactor,
     hash, lorder and 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.




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DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     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 _a_l_l 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 hash, compare and prefix store pointers to C
     functions. In DDDDBBBB____FFFFiiiilllleeee 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 ;
         }




                                                                        PPPPaaaaggggeeee 4444






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         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) ;
         }

         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 the section on _C_h_a_n_g_i_n_g _t_h_e _B_T_R_E_E _s_o_r_t _o_r_d_e_r for an example of using
     the compare template.

     If you are using the DB_RECNO interface and you intend making use of
     bval, you should check out the section on _T_h_e '_b_v_a_l' _O_p_t_i_o_n.

     DDDDeeeeffffaaaauuuulllltttt PPPPaaaarrrraaaammmmeeeetttteeeerrrrssss

     It is possible to omit some or all of the final 4 parameters in the call
     to 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:

         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:

         tie %A, "DB_File" ;

     is equivalent to:

         tie %A, "DB_File", undef, O_CREAT|O_RDWR, 0666, $DB_HASH ;

     See the section on _I_n _M_e_m_o_r_y _D_a_t_a_b_a_s_e_s for a discussion on the use of
     undef in place of a filename.

     IIIInnnn MMMMeeeemmmmoooorrrryyyy DDDDaaaattttaaaabbbbaaaasssseeeessss






                                                                        PPPPaaaaggggeeee 5555






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     Berkeley DB allows the creation of in-memory databases by using NULL
     (that is, a (char *)0 in C) in place of the filename.  DDDDBBBB____FFFFiiiilllleeee uses undef
     instead of NULL to provide this functionality.

DDDDBBBB____HHHHAAAASSSSHHHH
     The DB_HASH file format is probably the most commonly used of the three
     file formats that DDDDBBBB____FFFFiiiilllleeee supports. It is also very straightforward to
     use.

     AAAA SSSSiiiimmmmpppplllleeee EEEExxxxaaaammmmpppplllleeee

     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 ) ;

         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.





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DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



DDDDBBBB____BBBBTTTTRRRREEEEEEEE
     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.

     CCCChhhhaaaannnnggggiiiinnnngggg tttthhhheeee BBBBTTTTRRRREEEEEEEE ssssoooorrrrtttt oooorrrrddddeeeerrrr

     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 ;

         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




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DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     There are a few point to bear in mind if you want to change the ordering
     in a BTREE database:

     1.   The new compare function must be specified when you create the
          database.

     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.

     HHHHaaaannnnddddlllliiiinnnngggg DDDDuuuupppplllliiiiccccaaaatttteeee KKKKeeeeyyyyssss

     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 $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 (keys %h)
           { print "$_  -> $h{$_}\n" }

         untie %h ;

     Here is the output:







                                                                        PPPPaaaaggggeeee 8888






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         Smith   -> John
         Wall    -> Larry
         Wall    -> Larry
         Wall    -> Larry
         mouse   -> mickey

     As you can see 3 records have been successfully created with key Wall -
     the only thing is, when they are retrieved from the database they _s_e_e_m to
     have the same value, namely 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 seq.  This method allows sequential access to key/value pairs. See
     the section on _T_H_E _A_P_I _I_N_T_E_R_F_A_C_E for details of both the seq method and
     the API in general.

     Here is the script above rewritten using the seq API method.

         use strict ;
         use DB_File ;

         use vars qw($filename $x %h $status $key $value) ;



























                                                                        PPPPaaaaggggeeee 9999






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         $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 Wall.

     TTTThhhheeee _g_e_t__d_u_p() Method

     DDDDBBBB____FFFFiiiilllleeee comes with a utility method, called get_dup, to assist 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, $key.





                                                                       PPPPaaaaggggeeee 11110000






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     In list context, it returns all the values which match $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 get_dup like this:

         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 = $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 =>      []


     MMMMaaaattttcccchhhhiiiinnnngggg PPPPaaaarrrrttttiiiiaaaallll KKKKeeeeyyyyssss

     The BTREE interface has a feature which allows partial keys to be
     matched. This functionality is _o_n_l_y available when the 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.



                                                                       PPPPaaaaggggeeee 11111111






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     In the example script below, the 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:






                                                                       PPPPaaaaggggeeee 11112222






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         IN ORDER
         Smith -> John
         Wall  -> Larry
         Walls -> Brick
         mouse -> mickey

         PARTIAL MATCH
         Wa -> Wall  -> Larry
         A  -> Smith -> John
         a  -> mouse -> mickey


DDDDBBBB____RRRREEEECCCCNNNNOOOO
     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.

     TTTThhhheeee ''''bbbbvvvvaaaallll'''' OOOOppppttttiiiioooonnnn

     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
     "\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
     DDDDBBBB____FFFFiiiilllleeee? Well, the behavior defined in the quote above is quite useful,
     so DDDDBBBB____FFFFiiiilllleeee conforms it.

     That means that you can specify other options (e.g. cachesize) and still
     have bval default to "\n" for variable length records, and space for
     fixed length records.





                                                                       PPPPaaaaggggeeee 11113333






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     AAAA SSSSiiiimmmmpppplllleeee EEEExxxxaaaammmmpppplllleeee

     Here is a simple example that uses RECNO.

         use strict ;
         use DB_File ;

         my @h ;
         tie @h, "DB_File", "text", 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" ;

         # 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:

         Element 1 Exists with value blue
         The last element is yellow
         The 2nd last element is blue


     EEEExxxxttttrrrraaaa MMMMeeeetttthhhhooooddddssss

     As you can see from the example above, the tied array interface is quite
     limited. To make the interface more useful, a number of methods are
     supplied with DDDDBBBB____FFFFiiiilllleeee to simulate the standard array operations that are
     not currently implemented in Perl's tied array interface. All these
     methods are accessed via the object returned from the tie call.

     Here are the methods:

     $$$$XXXX---->>>>ppppuuuusssshhhh((((lllliiiisssstttt)))) ;;;;
          Pushes the elements of list to the end of the array.

     $$$$vvvvaaaalllluuuueeee ==== $$$$XXXX---->>>>ppppoooopppp ;;;;
          Removes and returns the last element of the array.

     $$$$XXXX---->>>>sssshhhhiiiifffftttt
          Removes and returns the first element of the array.





                                                                       PPPPaaaaggggeeee 11114444






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     $$$$XXXX---->>>>uuuunnnnsssshhhhiiiifffftttt((((lllliiiisssstttt)))) ;;;;
          Pushes the elements of list to the start of the array.

     $$$$XXXX---->>>>lllleeeennnnggggtttthhhh
          Returns the number of elements in the array.

     AAAAnnnnooootttthhhheeeerrrr EEEExxxxaaaammmmpppplllleeee

     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 the
     section on _T_H_E _A_P_I _I_N_T_E_R_F_A_C_E).

         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" ;



                                                                       PPPPaaaaggggeeee 11115555






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         # 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









                                                                       PPPPaaaaggggeeee 11116666






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         REVERSE again
         5: last
         4: three
         3: Newbie
         2: one
         1: New One
         0: first

     Notes:

     1.   Rather than iterating through the array, @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) )


     2.   Notice that both times the put method was used the record index was
          specified using a variable, $i, rather than the literal value
          itself. This is because put will return the record number of the
          inserted line via that parameter.

TTTTHHHHEEEE AAAAPPPPIIII IIIINNNNTTTTEEEERRRRFFFFAAAACCCCEEEE
     As well as accessing Berkeley DB using a tied hash or array, it is also
     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.

             $db = tie %hash, "DB_File", "filename" ;

     Once you have done that, you can access the Berkeley DB API functions as
     DDDDBBBB____FFFFiiiilllleeee methods directly like this:

             $db->put($key, $value, R_NOOVERWRITE) ;

     IIIImmmmppppoooorrrrttttaaaannnntttt:::: If you have saved a copy of the object returned from tie, the
     underlying database file will _n_o_t be closed until both the tied variable
     is untied and all copies of the saved object are destroyed.








                                                                       PPPPaaaaggggeeee 11117777






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         use DB_File ;
         $db = tie %hash, "DB_File", "filename"
             or die "Cannot tie filename: $!" ;
         ...
         undef $db ;
         untie %hash ;

     See the section on _T_h_e _u_n_t_i_e() _G_o_t_c_h_a for more details.

     All the functions defined in the _d_b_o_p_e_n manpage are available except for
     _c_l_o_s_e() and _d_b_o_p_e_n() itself. The DDDDBBBB____FFFFiiiilllleeee method interface to the
     supported functions have been implemented to mirror the way Berkeley DB
     works whenever possible. In particular note that:

     +o    The methods return a status value. All return 0 on success.  All
          return -1 to signify an error and set $! 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.

     +o    Whenever a Berkeley DB function returns data via one of its
          parameters, the equivalent DDDDBBBB____FFFFiiiilllleeee method does exactly the same.

     +o    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: $!" ;




                                                                       PPPPaaaaggggeeee 11118888






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



              # 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) ;


     All the constants defined in the _d_b_o_p_e_n manpage 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 methods available.

     $$$$ssssttttaaaattttuuuussss ==== $$$$XXXX---->>>>ggggeeeetttt(((($$$$kkkkeeeeyyyy,,,, $$$$vvvvaaaalllluuuueeee [[[[,,,, $$$$ffffllllaaaaggggssss]]]])))) ;;;;
          Given a key ($key) this method reads the value associated with it
          from the database. The value read from the database is returned in
          the $value parameter.

          If the key does not exist the method returns 1.

          No flags are currently defined for this method.

     $$$$ssssttttaaaattttuuuussss ==== $$$$XXXX---->>>>ppppuuuutttt(((($$$$kkkkeeeeyyyy,,,, $$$$vvvvaaaalllluuuueeee [[[[,,,, $$$$ffffllllaaaaggggssss]]]])))) ;;;;
          Stores the key/value pair in the database.

          If you use either the R_IAFTER or R_IBEFORE flags, the $key
          parameter will have the record number of the inserted key/value pair
          set.

          Valid flags are R_CURSOR, R_IAFTER, R_IBEFORE, R_NOOVERWRITE and
          R_SETCURSOR.

     $$$$ssssttttaaaattttuuuussss ==== $$$$XXXX---->>>>ddddeeeellll(((($$$$kkkkeeeeyyyy [[[[,,,, $$$$ffffllllaaaaggggssss]]]])))) ;;;;
          Removes all key/value pairs with key $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.

     $$$$ssssttttaaaattttuuuussss ==== $$$$XXXX---->>>>ffffdddd ;;;;
          Returns the file descriptor for the underlying database.

          See the section on _L_o_c_k_i_n_g _D_a_t_a_b_a_s_e_s for an example of how to make
          use of the fd method to lock your database.






                                                                       PPPPaaaaggggeeee 11119999






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     $$$$ssssttttaaaattttuuuussss ==== $$$$XXXX---->>>>sssseeeeqqqq(((($$$$kkkkeeeeyyyy,,,, $$$$vvvvaaaalllluuuueeee,,,, $$$$ffffllllaaaaggggssss)))) ;;;;
          This interface allows sequential retrieval from the database. See
          the _d_b_o_p_e_n manpage for full details.

          Both the $key and $value parameters will be set to the key/value
          pair read from the database.

          The flags parameter is mandatory. The valid flag values are
          R_CURSOR, R_FIRST, R_LAST, R_NEXT and R_PREV.

     $$$$ssssttttaaaattttuuuussss ==== $$$$XXXX---->>>>ssssyyyynnnncccc(((([[[[$$$$ffffllllaaaaggggssss]]]])))) ;;;;
          Flushes any cached buffers to disk.

          R_RECNOSYNC is the only valid flag at present.

HHHHIIIINNNNTTTTSSSS AAAANNNNDDDD TTTTIIIIPPPPSSSS
     LLLLoooocccckkkkiiiinnnngggg DDDDaaaattttaaaabbbbaaaasssseeeessss

     Concurrent access of a read-write database by several parties requires
     them all to use some kind of locking.  Here's an example of Tom's that
     uses the _f_d method to get the file descriptor, and then a careful _o_p_e_n()
     to give something Perl will _f_l_o_c_k() for you.  Run this repeatedly in the
     background to watch the locks granted in proper order.

         use DB_File;

         use strict;

         sub LOCK_SH { 1 }
         sub LOCK_EX { 2 }
         sub LOCK_NB { 4 }
         sub LOCK_UN { 8 }

         my($oldval, $fd, $db, %db, $value, $key);

         $key = shift || 'default';
         $value = shift || 'magic';

         $value .= " $$";

         $db = tie(%db, 'DB_File', '/tmp/foo.db', O_CREAT|O_RDWR, 0644)
                 || die "dbcreat /tmp/foo.db $!";
         $fd = $db->fd;
         print "$$: db fd is $fd\n";
         open(DB_FH, "+<&=$fd") || die "dup $!";

         unless (flock (DB_FH, LOCK_SH | LOCK_NB)) {
             print "$$: CONTENTION; can't read during write update!
                         Waiting for read lock ($!) ....";
             unless (flock (DB_FH, LOCK_SH)) { die "flock: $!" }
         }
         print "$$: Read lock granted\n";



                                                                       PPPPaaaaggggeeee 22220000






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         $oldval = $db{$key};
         print "$$: Old value was $oldval\n";
         flock(DB_FH, LOCK_UN);

         unless (flock (DB_FH, LOCK_EX | LOCK_NB)) {
             print "$$: CONTENTION; must have exclusive lock!
                         Waiting for write lock ($!) ....";
             unless (flock (DB_FH, LOCK_EX)) { die "flock: $!" }
         }

         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";


     SSSShhhhaaaarrrriiiinnnngggg DDDDaaaattttaaaabbbbaaaasssseeeessss WWWWiiiitttthhhh CCCC AAAApppppppplllliiiiccccaaaattttiiiioooonnnnssss

     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.

     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 ~/._n_e_t_s_c_a_p_e/_h_i_s_t_o_r_y._d_b. 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 _g_g_h
     script (available from your nearest CPAN archive in
     _a_u_t_h_o_r_s/_i_d/_T_O_M_C/_s_c_r_i_p_t_s/_n_s_h_i_s_t._g_z).

         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";



                                                                       PPPPaaaaggggeeee 22221111






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         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 ;


     TTTThhhheeee _u_n_t_i_e() Gotcha

     If you make use of the Berkeley DB API, it is _v_e_r_y strongly recommended
     that you read the section on _T_h_e _u_n_t_i_e _G_o_t_c_h_a in the _p_e_r_l_t_i_e manpage.

     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 DDDDBBBB____FFFFiiiilllleeee
     perspective:

         use DB_File ;
         use Fcntl ;

         my %x ;
         my $X ;

         $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_TRUNC
             or die "Cannot tie first time: $!" ;

         $x{123} = 456 ;

         untie %x ;





                                                                       PPPPaaaaggggeeee 22222222






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



         tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
             or die "Cannot tie second time: $!" ;

         untie %x ;

     When run, the script will produce this error message:

         Cannot tie second time: Invalid argument at bad.file line 14.

     Although the error message above refers to the second _t_i_e() statement in
     the script, the source of the problem is really with the _u_n_t_i_e()
     statement that precedes it.

     Having read the _p_e_r_l_t_i_e manpage you will probably have already guessed
     that the error is caused by the extra copy of the tied object stored in
     $X.  If you haven't, then the problem boils down to the fact that the
     DDDDBBBB____FFFFiiiilllleeee destructor, DESTROY, will not be called until _a_l_l references to
     the tied object are destroyed. Both the tied variable, %x, and $X above
     hold a reference to the object. The call to _u_n_t_i_e() will destroy the
     first, but $X still holds a valid reference, so the destructor will not
     get called and the database file _t_s_t._f_i_l 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.

     If you run the script with the -w flag the error message becomes:

         untie attempted while 1 inner references still exist at bad.file line 12.
         Cannot tie second time: Invalid argument at bad.file line 14.

     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:

         ...
         $x{123} = 456 ;

         undef $X ;
         untie %x ;

         $X = tie %x, 'DB_File', 'tst.fil' , O_RDWR|O_CREAT
         ...


CCCCOOOOMMMMMMMMOOOONNNN QQQQUUUUEEEESSSSTTTTIIIIOOOONNNNSSSS
     WWWWhhhhyyyy iiiissss tttthhhheeeerrrreeee PPPPeeeerrrrllll ssssoooouuuurrrrcccceeee iiiinnnn mmmmyyyy ddddaaaattttaaaabbbbaaaasssseeee????

     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



                                                                       PPPPaaaaggggeeee 22223333






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     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.

     HHHHoooowwww ddddoooo IIII ssssttttoooorrrreeee ccccoooommmmpppplllleeeexxxx ddddaaaattttaaaa ssssttttrrrruuuuccccttttuuuurrrreeeessss wwwwiiiitttthhhh DDDDBBBB____FFFFiiiilllleeee????

     Although DDDDBBBB____FFFFiiiilllleeee cannot do this directly, there is a module which can
     layer transparently over DDDDBBBB____FFFFiiiilllleeee to accomplish this feat.

     Check out the MLDBM module, available on CPAN in the directory
     _m_o_d_u_l_e_s/_b_y-_m_o_d_u_l_e/_M_L_D_B_M.

     WWWWhhhhaaaatttt ddddooooeeeessss """"IIIInnnnvvvvaaaalllliiiidddd AAAArrrrgggguuuummmmeeeennnntttt"""" mmmmeeeeaaaannnn????

     You will get this error message when one of the parameters in the 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:

     1.   Attempting to reopen a database without closing it.

     2.   Using the O_WRONLY flag.

     WWWWhhhhaaaatttt ddddooooeeeessss """"BBBBaaaarrrreeeewwwwoooorrrrdddd ''''DDDDBBBB____FFFFiiiilllleeee'''' nnnnooootttt aaaalllllllloooowwwweeeedddd"""" mmmmeeeeaaaannnn????

     You will encounter this particular error message when you have the 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 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 use strict in all your scripts.




                                                                       PPPPaaaaggggeeee 22224444






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



HHHHIIIISSSSTTTTOOOORRRRYYYY
     Moved to the Changes file.

BBBBUUUUGGGGSSSS
     Some older versions of Berkeley DB had problems with fixed length 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.

AAAAVVVVAAAAIIIILLLLAAAABBBBIIIILLLLIIIITTTTYYYY
     DDDDBBBB____FFFFiiiilllleeee comes with the standard Perl source distribution. Look in the
     directory _e_x_t/_D_B__F_i_l_e. 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 the CPAN entry
     in the _p_e_r_l_m_o_d manpage for details), in the directory _m_o_d_u_l_e_s/_b_y-
     _m_o_d_u_l_e/_D_B__F_i_l_e.

     This version of DDDDBBBB____FFFFiiiilllleeee 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 _h_t_t_p://_w_w_w._s_l_e_e_p_y_c_a_t._c_o_m/_d_b. The
     ftp equivalent is _f_t_p._s_l_e_e_p_y_c_a_t._c_o_m:/_p_u_b. Both versions 1 and 2 of
     Berkeley DB are available there.

     Alternatively, Berkeley DB version 1 is available at your nearest CPAN
     archive in _s_r_c/_m_i_s_c/_d_b._1._8_5._t_a_r._g_z.

     If you are running IRIX, then get Berkeley DB version 1 from
     _h_t_t_p://_r_e_a_l_i_t_y._s_g_i._c_o_m/_a_r_i_e_l. It has the patches necessary to compile
     properly on IRIX 5.3.

CCCCOOOOPPPPYYYYRRRRIIIIGGGGHHHHTTTT
     Copyright (c) 1997 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 DDDDBBBB____FFFFiiiilllleeee 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.

     The license for Berkeley DB version 2, and how it relates to DB_File does
     need some extra clarification. Here are are few words taken from the
     Berkeley DB FAQ regarding the version 2 license:

         The major difference is that the license for DB 2.0, when
         downloaded from the net, requires that the software that
         uses DB 2.0 be freely redistributable.

     That means that if you want to use DB_File, and you have changed either
     the source for Berkeley DB or Perl, then the changes must be freely



                                                                       PPPPaaaaggggeeee 22225555






DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))



     available.

     In the case of Perl, the term source refers to the complete source code
     for Perl (e.g. sv.c, toke.c, perl.h) and any external modules that you
     are using (e.g. DB_File, Tk).

     Note that any Perl scripts that you write are your property - this
     includes scripts that make use of DB_File. Neither the Perl license or
     the Berkeley DB license place any restriction on what you have to 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 the section on _A_U_T_H_O_R
     for details.

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     the _p_e_r_l(_1) manpage, the _d_b_o_p_e_n(_3) manpage, the _h_a_s_h(_3) manpage, the
     _r_e_c_n_o(_3) manpage, the _b_t_r_e_e(_3) manpage

AAAAUUUUTTTTHHHHOOOORRRR
     The DB_File interface was written by Paul Marquess
     <[e-mail]>.  Questions about the DB system itself may be
     addressed to <[e-mail]<gt>.
































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DDDDBBBB____FFFFiiiilllleeee((((3333))))                                                          DDDDBBBB____FFFFiiiilllleeee((((3333))))























































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