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:
-
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 perlfunc/umask.)
On failure, the tie call returns an undefined value and probably
sets $! to contain the reason the file could not be tied.
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 perlfunc/tie, perldbmfilter, Fcntl
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