MirOS Manual: NDBM_File(3p)


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 manipu-
     late 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.

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

     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

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