CliApp.php

<?php

$form = new Zend_Form();
$form->setElements(array(
    new Zend_Form_Element_Text('colour', array(
        'required' => true,
        'label' => 'Please enter acceptable colours (blue, green or red)',
        'validators' => array(
            array('NotEmpty', true, array(
                'messages' => 'A colour is required'
            )),
            array('InArray', true, array(
                'messages' => 'Colour is uncceptable',
                'haystack' => array('blue', 'green', 'red')
            ))
        )
    )),
    new Zend_Form_Element_Text('someOtherInput', array(
        'required' => true,
        'label' => 'Please enter acceptable words (thank, you)',
        'validators' => array(
            array('NotEmpty', true, array(
                'messages' => 'A word is required'
            )),
            array('InArray', true, array(
                'messages' => 'Word is uncceptable',
                'haystack' => array('thank', 'you')
            ))
        )
    ))
));

$prompt = new Cli_Prompt($form);
$prompt->prompt();
//now we may do other stuff as we are guaranteed to have valid input

CliPrompt.php

<?php

class Cli_Prompt
{
    /**
     * @var Zend_Form
     */
    protected $_form = null;
    
    /**
     * Prompt constructor
     *
     * @param Zend_Form $form 
     */
    public function __construct(Zend_Form $form) {
        if (php_sapi_name() !== 'cli') {
            throw new RuntimeException('Class can only be used from the command line');
        }
        $this->_form = $form;
    }
    
    /**
     * Prompts the user for input and validates the input
     *
     * @return Zend_Form
     */
    public function prompt()
    {
        $elements = $this->_form->getElements();
        $errorFilter = new Filter_FormErrors();
        $colour = new Cli_Colour();
        foreach ($elements as $element)
        {
            $firstRun = true;
            $element instanceof Zend_Form_Element;
            while (!$element->isValid($element->getValue())) {
                $label = '';
                if (!$firstRun) {
                    $label = $element->getLabel() .  
                            ' (Error: ' . $colour->getColoredString(
                                    $errorFilter->filter($element->getMessages()) , 'red', 'light_gray') . 
                            '): ';
                } else {
                    $label = $element->getLabel() . ': ';
                    $firstRun = false;
                }
                $input = readline($label);
                $element->setValue($input);
            }
        }
        return $this->_form;
    }
}

FilterFormErrors.php

<?php

class Filter_FormErrors implements Zend_Filter_Interface
{
    /**
     * Filter method
     *
     * @param array $errors
     * @return string
     */
    public function filter($errors) {
        if (!is_array($errors)) {
            $errors = (array)$errors;
        }
        $flatten = array();
        array_walk_recursive($errors, function($value, $key) use (&$flatten) {
                    $flatten[] = $value;
                });
        $message = implode(', ', $flatten);
        return $message;
    }
}