Perl5 リファレンス

       dbmopen HASH,DBNAME,MASK
               [This function has been largely superseded by the
               `tie' function.]

               This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or
               Berkeley DB file to a hash.  HASH is the name of
               the hash.  (Unlike normal `open', the first
               argument is not a filehandle, even though it looks
               like one).  DBNAME is the name of the database
               (without the .dir or .pag extension if any).  If
               the database does not exist, it is created with
               protection specified by MASK (as modified by the
               `umask').  If your system supports only the older
               DBM functions, you may perform only one `dbmopen'
               in your program.  In older versions of Perl, if
               your system had neither DBM nor ndbm, calling
               `dbmopen' produced a fatal error; it now falls
               back to sdbm(3).

               If you don't have write access to the DBM file,
               you can only read hash variables, not set them.
               If you want to test whether you can write, either
               use file tests or try setting a dummy hash entry
               inside an `eval', which will trap the error.

               Note that functions such as `keys' and `values'
               may return huge lists when used on large DBM
               files.  You may prefer to use the `each' function
               to iterate over large DBM files.  Example:

                   # print out history file offsets
                   while (($key,$val) = each %HIST) {
                       print $key, ' = ', unpack('L',$val), "\n";

               See also the AnyDBM_File manpage for a more
               general description of the pros and cons of the
               various dbm approaches, as well as the DB_File
               manpage for a particularly rich implementation.

               You can control which DBM library you use by
               loading that library before you call dbmopen():

                   use DB_File;
                   dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
                       or die "Can't open netscape history file: $!";