SDBM_File - Tied access to sdbm files |
SDBM_File - Tied access to sdbm files
use Fcntl; # For O_RDWR, O_CREAT, etc. use SDBM_File;
tie(%h, 'SDBM_File', 'filename', O_RDWR|O_CREAT, 0666) or die "Couldn't tie SDBM file 'filename': $!; aborting";
# Now read and change the hash $h{newkey} = newvalue; print $h{oldkey}; ...
untie %h;
SDBM_File
establishes a connection between a Perl hash variable and
a file in SDBM_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 SDBM_File
with the Perl built-in tie
function to establish
the connection between the variable and the file. The arguments to
tie
should be:
"SDBM_File"
. (Ths tells Perl to use the SDBM_File
package to perform the functions of the hash.)
O_RDONLY
O_WRONLY
O_RDWR
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.
On failure, the tie
call returns an undefined value and probably
sets $!
to contain the reason the file could not be tied.
sdbm 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 SDBM 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 the perlfunc manpage, the perldbmfilter manpage, the Fcntl manpage
SDBM_File - Tied access to sdbm files |