GNU/Linux |
CentOS 2.1AS(Slurm) |
|
NDBM_File(3pm) |
NDBM_File − Tied access to ndbm files
use Fcntl; # For O_RDWR, O_CREAT, etc. use NDBM_File; # Now read and change the hash $h{newkey} = newvalue; print $h{oldkey}; ... untie %h;
"NDBM_File" establishes a connection between a Perl hash variable and a file in NDBM_File format;. You can manipulate the data in the file just as if it were in a Perl hash, but when your program exits, the data will remain in the file, to be used the next time your program runs.
Use "NDBM_File" with the Perl built-in "tie" function to establish the connection between the variable and the file. The arguments to "tie" should be:
1. |
The hash variable you want to tie. | ||
2. |
The string ""NDBM_File"". (Ths tells Perl to use the "NDBM_File" package to perform the functions of the hash.) | ||
3. |
The name of the file you want to tie to the hash. | ||
4. |
Flags. Use one of: |
""O_RDONLY""
Read-only access to the data in the file.
""O_WRONLY""
Write-only access to the data in the file.
""O_RDWR""
Both read and write access.
If you want to create the file if it does not exist, add "O_CREAT" to any of these, as in the example. If you omit "O_CREAT" and the file does not already exist, the "tie" call will fail.
5. |
The default permissions to use if a new file is created. The actual permissions will be modified by the user’s umask, so you should probably use 0666 here. (See the umask entry in the perlfunc manpage.) |
On failure, the "tie" call returns an undefined value and probably sets "$!" 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.
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 the tie entry in the perlfunc manpage, the perldbmfilter manpage, the Fcntl manpage
NDBM_File(3pm) |