Perl 5 version 24.3 documentation

NDBM_File

NAME

NDBM_File - Tied access to ndbm files

SYNOPSIS

  1.   use Fcntl;   # For O_RDWR, O_CREAT, etc.
  2.   use NDBM_File;
  4.   tie(%h, 'NDBM_File', 'filename', O_RDWR|O_CREAT, 0666)
  5.     or die "Couldn't tie NDBM file 'filename': $!; aborting";
  7.   # Now read and change the hash
  8.   $h{newkey} = newvalue;
  9.   print $h{oldkey};
  10.   ...
  12.   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:

  • The hash variable you want to tie.

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

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

  • 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.

  • 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.)

    • 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, perldbmfilter, Fcntl