Perl in a Nutshell, 2nd Edition

DB_File

Ties a Perl hash to one of the Berkeley DB database types and lets you use functions provided in the DB API:

[$X =] tie %hash,  "DB_File", $filename [, $flags, $mode, $DB_HASH];
[$X =] tie %hash,  "DB_File", $filename, $flags, $mode, $DB_BTREE;
[$X =] tie @array, "DB_File", $filename, $flags, $mode, $DB_RECNO;

The types are:

$DB_HASH

Stores key/data pairs in data files. Equivalent to other hashing packages such as DBM, NDBM, ODBM, GDBM, and SDBM.

$DB_BTREE

Stores key/data pairs in a binary tree.

$DB_RECNO

Uses a record (line) number to access fixed-length and variable-length flat text files through the same key/value-pair interface as in $DB_HASH and $DB_BTREE.

After you’ve tied a hash to a database:

$db = tie %hash, "DB_File", "filename";

you can access the Berkeley DB API functions:

$db->put($key, $value, R_NOOVERWRITE);  # Invoke the DB "put" function

All the functions defined in the dbopen(3) manpage are available except close and dbopen itself. The constants defined in the dbopen manpage are also available.

The following are the functions available (the comments note only the differences from the equivalent C function).