10.2. Using DBM Databases

Problem

You want a more stable and scalable way to store simple data than what text files offer.

Solution

Use the DBA abstraction layer to access a DBM-style database:

$dbh = dba_open('fish.db','c','gdbm') or die($php_errormsg);

// retrieve and change values
if (dba_exists('flounder',$dbh)) {
  $flounder_count = dba_fetch('flounder',$dbh);
  $flounder_count++;
  dba_replace('flounder',$flounder_count, $dbh);
  print "Updated the flounder count.";
} else {
  dba_insert('flounder',1, $dbh);
  print "Started the flounder count.";
}

// no more tilapia
dba_delete('tilapia',$dbh);

// what fish do we have?
for ($key = dba_firstkey($dbh);  $key !== false; $key = dba_nextkey($dbh)) {
   $value = dba_fetch($key, $dbh);
   print "$key: $value\n";
}

dba_close($dbh);

Discussion

PHP can support a few different kinds of DBM backends: GDBM, NDBM, DB2, DB3, DBM, and CDB. The DBA abstraction layer lets you use the same functions on any DBM backend. All these backends store key/value pairs. You can iterate through all the keys in a database, retrieve the value associated with a particular key, and find if a particular key exists. Both the keys and the values are strings.

The following program maintains a list of usernames and passwords in a DBM database. The username is the first command-line argument, and the password is the second argument. If the given username already exists in the database, the password is changed to the given password; otherwise the user and password combination are ...

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