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




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 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 v5.24.0                      2016-03-01                    NDBM_File(3pm)

perl 5.24 - Generated Fri Nov 18 16:30:00 CST 2016
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