


NDBM_File(3p)    Perl Programmers Reference Guide   NDBM_File(3p)


NAME
       NDBM_File - Tied access to ndbm files

SYNOPSIS
         use Fcntl;   # For O_RDWR, O_CREAT, etc.
         use NDBM_File;

         tie(%h, 'NDBM_File', 'filename', O_RDWR|O_CREAT, 0666)
           or die "Couldn't tie NDBM file 'filename': $!; aborting";

         # Now read and change the hash
         $h{newkey} = newvalue;
         print $h{oldkey};
         ...

         untie %h;

DESCRIPTION
       "NDBM_File" establishes a connection between a Perl hash
       variable and a file in NDBM_File format;.  You can
       manipulate the data in the file just as if it were in a
       Perl hash, but when your program exits, the data will
       remain in the file, to be used the next time your program
       runs.

       Use "NDBM_File" with the Perl built-in "tie" function to
       establish the connection between the variable and the
       file.  The arguments to "tie" should be:

       1.  The hash variable you want to tie.

       2.  The string "NDBM_File".  (Ths tells Perl to use the
           "NDBM_File" package to perform the functions of the
           hash.)

       3.  The name of the file you want to tie to the hash.

       4.  Flags.  Use one of:

           "O_RDONLY"
             Read-only access to the data in the file.

           "O_WRONLY"
             Write-only access to the data in the file.

           "O_RDWR"
             Both read and write access.

           If you want to create the file if it does not exist,
           add "O_CREAT" to any of these, as in the example.  If
           you omit "O_CREAT" and the file does not already
           exist, the "tie" call will fail.

       5.  The default permissions to use if a new file is



perl v5.10.1                2009-10-12                          1





NDBM_File(3p)    Perl Programmers Reference Guide   NDBM_File(3p)


           created.  The actual permissions will be modified by
           the user's umask, so you should probably use 0666
           here. (See "umask" in perlfunc.)

DIAGNOSTICS
       On failure, the "tie" call returns an undefined value and
       probably sets $! to contain the reason the file could not
       be tied.

   "ndbm store returned -1, errno 22, key "..." at ..."
       This warning is emitted when you try to store a key or a
       value that is too long.  It means that the change was not
       recorded in the database.  See BUGS AND WARNINGS below.

BUGS AND WARNINGS
       There are a number of limits on the size of the data that
       you can store in the NDBM file.  The most important is
       that the length of a key, plus the length of its
       associated value, may not exceed 1008 bytes.

       See "tie" in perlfunc, perldbmfilter, Fcntl




































perl v5.10.1                2009-10-12                          2


