If you ever wonder where that 'StringEquals' validator rule taken as example from the Zend_Filter_Input documentation page results in an error like below, well read again. It was clearly stated as 'hypothetical'.

Plugin by name 'StringEquals' was not found in the registry; used paths: Zend_Validate_: Zend/Validate/

Given such validator would be useful on a number of situations i.e. confirming passwords, emails, etc. I present to you my own version of the class.

 
<?php
class Zend_Validate_StringEquals extends Zend_Validate_Abstract
{
    const NOT_EQUAL	= 'stringNotEqual';
    const MISSING	= 'stringMissing';
 
    /**
     * @var array
     */
    protected $_messageTemplates = array(
        self::NOT_EQUAL	=> "%field1% and %field2% are not equal.",
        self::MISSING	=> "One or both strings are missing."
    );
 
    /**
     * @var array
     */
    protected $_messageVariables = array(
        'field1' => '_field1',
        'field2' => '_field2'
    );
 
    protected $_case = false;
    protected $_field1 = null;
    protected $_field2 = null;
 
    /**
     * Sets validator options
     *
     * @param  boolean $case
     * @return void
     */
    public function __construct($case = false)
    {
        $this->_case = $case;
    }
 
    /**
     * Defined by Zend_Validate_Interface
     *
     * Returns true if and only if the the 2 strings are equal
     *
     * @param  array $value
     * @return boolean
     */
    public function isValid($value)
    {
    	if(!is_array($value) OR sizeof($value) < 2) {
			$this->_error(self::MISSING);
    	}
 
    	$this->_field1 = array_shift($value);
    	$this->_field2 = array_shift($value);
 
        if($this->_case === true) $function = 'strcmp';
        else $function = 'strcasecmp';
 
        if(0 !== $function($this->_field1,$this->_field2)) $this->_error(self::NOT_EQUAL);
 
        if (count($this->_messages)) {
            return false;
        } else {
            return true;
        }
    }
}
 

Here is a sample test case. Validate password and confirm password elements represented by 'password' and 'cpassword' element names respectively.

 
$filters = array('password' => 'StringTrim', 'cpassword' => 'StringTrim');
$validators = array(
    'Password' => array(
        'presence' => 'required',
        array('StringLength',5,15),
        'fields' => 'password',
        'messages' => "Passwords must be between 5 and 15 characters in length."),
    'Confirm password' => array(
        array('StringEquals'),
        'fields' => array('password','cpassword'),
        'messages' => array(
            0 => array(
                Zend_Validate_StringEquals::NOT_EQUAL => "Passwords does not match.",
                Zend_Validate_StringEquals::MISSING => "Both password fields must be filled."))));
 
$inputdata = new Zend_Filter_Input($filter,$validators,$_POST,$options);