NDBM_File(3) Tied access to ndbm files


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;


"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:
Read-only access to the data in the file.
Write-only access to the data in the file.
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'' in perlfunc.)


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.


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