ndbm_file(3)
NAME
NDBM_File - Tied access to ndbm files
SYNOPSIS
use Fcntl; # For O_RDWR, O_CREAT, etc.
use NDBM_File;
# 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. - 5. The default permissions to use if a new file is cre
ated. 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 emmitted 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 associ
ated value, may not exceed 1008 bytes.
- See "tie" in perlfunc, perldbmfilter, Fcntl