For anyone interested in removing a user from a group, you can use ldap_mod_del() as follows:

$group = 'CN=mygroup,OU=myOU,DC=mydomain,DC=com';

$group_info['member'] = 'CN=User\, Test,CN=Users,DC=mydomain,DC=com';

ldap_mod_del($ldap, $group, $group_info);

I have tested this using Active Directory on a Win 2K3 server.

To remove all of a particular attribute, feed it an empty array.

For example, to remove all members from a group:

<?php
ldap_mod_del($ldapconn,$groupDN,array("member" => array()));
?>

Te remove a user from a group in Apple's Open Directory, you need to also remove the members generated uid from the group.

Removing the users is as follows:

<?php

//setting variables
$ldapDN = "uid=myadmin,cn=users,dc=myserver,dc=com';
$ldapPass = "somepass";

$groupDn = 'cn=mygroup,cn=groups,dc=myserver,dc=com'
$removal = array(
    "memberuid"=>"username",
    "apple-group-memberguid"=>"846DE847-D73D-428D-83A8-B95B606C511B"
);

//connect and bind
$ldapconnect = ldap_connect("myserver.com",389);
ldap_bind($ldapconnect, $ldapDN, $ldapPass);

//removing member from group
ldap_mod_del($ldapconnect, $groupDn, $removal);

//unbind
ldap_unbind($ldapconnect);

?>

I have found that the syntax:

$entry["mail"] = ""; 

Will NOT delete the mail attribute using the OpenLDAP server.  You must specify the attribute value to delete it successfully, otherwise you will recieve an "Invalid Syntax" error from the server.

The error: "Inappropriate Matching" will be displayed if the attribute you are trying to delete has no equality rule in the schema.  I had a problem deleting the attribute facsimilieTelephoneNumber, and it was because my core.schema file did not have an EQUALITY definition for that attribute.  I copied the telephoneNumber EQUALITY rule and it worked perfectly.

We often need to delete "objectclass" below follows a simple code to make this successful removal.

$userdataModifydelSamba = array();
$userdataModifydelSamba['objectClass'] = array();
$userdataModifydelSamba['objectClass'][0] = 'sambaSamAccount';

$userdataModifydelSamba['sambasid'] = array();
$userdataModifydelSamba['sambantpassword'] = array();
$userdataModifydelSamba['sambahomedrive'] = array();
$userdataModifydelSamba['sambadomainname'] = array();
$userdataModifydelSamba['sambaacctflags'] = array();
$userdataModifydelSamba['sambaprimarygroupsid'] = array();
$userdataModifydelSamba['sambapwdlastset'] = array();

$sucess = @ldap_mod_del($connection, $dn, $result);
if(!$sucess)
{
   throw new Exception("error " . ldap_err2str(ldap_errno($connection)));
}

and please don't forget:
you can't delete all attributes, when at least one is required.

The above example has also been proven to work in the iPlanet / Sun One Directory Server 5.0/5.1. As an example:

$attrs["mail"] = array();
ldap_mod_del($ldapConnID,$dn,$attrs);

or

$attrs["mail"] = array();
$attrs["telephonenumber"] = array();
ldap_mod_del($ldapConnID,$dn,$attrs);

This will remove all occurences of attributes in the entry specified by the dn.

At least with OpenLDAP 1.2.x
to remove an attribute regardless of it's value you have to assign:

$attrs["AttributeName"]=array();

after ldap_mod_del($ds,$dn,$attrs)
all occurences of AttributeName will be removed

To remove all instances of an attribute:

$entry["attrname"][]="value1";
$entry["attrname"][]="value2";
...
$entry["attrname"][]="valueN";

ldap_mod_del($ds, $dn, $entry);

<pre> 
uid: testuser 
mail: [email protected] 
mail: [email protected] 
</pre> 

How to remove the values of mail so that only the second value for mail exists:

<pre> 
$entry["mail"] = "[email protected]"; 
$result = ldap_mod_del($connID, $dn, $entry); 
</pre> 

if you want to remove all instances of an attribute.....
==> 
<pre> 
$entry["mail"][0] = "[email protected]"; 
$entry["mail"][1] = "[email protected]"; 
$result = ldap_mod_del($connID, $dn, $entry); 
</pre> 

are not?

Using ldap_modify with a blank string works if you aren't propagating your LDAP database, even though it returns the error. Still, I'd say don't do it, as it smacks of something that will be fixed in a future version.

After a couple hours of searching and not finding anything on the ldap_mod_del function worth anything, I started trying to figure out myself what format the "array entry" parameter needed to be in.  Here is what I found:

The entry array is a hash with the attribute name as the hash key and the specific value you want deleted for that attribute as the corresponding hash value.

-- Example

Current values for the attributes of of a particular entry:

     uid: testuser
     mail: [email protected]
     mail: [email protected]

How to remove the first value of mail so that only the second value for mail exists:

     $entry["mail"] = "[email protected]";
     $result = ldap_mod_del($connID, $dn, $entry);

So if you want to remove all instances of an attribute, you have to do it one by one.

To remove all instances of an attribute you can use ldap_modify with an empty value for that attribute.

$entry["mail"] = ""; 
$result = ldap_modify($connID, $dn, $entry);