When doing a dba_exists() or dba_fetch() on a ndbm database then one has to attach a "\0" character to the key string that it matches.

Configuration:

./configure --prefix=/opt/apache \
            --with-apxs2=/opt/apache/bin/apxs \
            --enable-safe-mode \
            --with-openssl=/opt/openssl \
            --with-ldap=/opt/openldap \
            --with-imap=/opt/uw-imap \
            --with-config-file-path=/opt/apache/conf \
            --enable-dba \
            --with-dbm \
            --with-ndbm

Script that explains the problem:

$alias = "some string";
$id = dba_open($ALIASES_FILE, 'r', 'ndbm');
$key = dba_firstkey($id); # $key contains trailing \0 char
print dba_fetch($alias, $id); # does not match
print dba_fetch("$alias\0", $id); # works
dba_close($id);

Don't know whether it works with other dba handlers or other PHP version.