NDBM_File − 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:
|
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.) |
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