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:

The hash variable you want to tie.
The string "SDBM_File". (Ths tells Perl to use the SDBM_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:

Read-only access to the data in the file.
Write-only access to the data in the file.
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.

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 perlfunc/tie, perldbmfilter, Fcntl