How to Rewrite / Override block in magento

How to Rewrite / Override block in magento

Here we are Overriding / Rewriting magento block of Mage_Catalog_Block_Product_View with custom module named Chand_Software.

(1) Create module file in app/etc/modules/Chand_Software.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Chand_Software>
            <active>true</active>
            <codePool>local</codePool>
        </Chand_Software>
    </modules>
</config>

(2) Create module config file in app/code/local/Chand/Software/etc/config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Chand_Software>
            <version>1.0.0</version>
        </Chand_Software>
    </modules>
    <global>
        <blocks>
            <catalog>  // This is the block identifier which we want rewrite
                <rewrite>
                    <product_view>Chand_Software_Block_Product_View</product_view>
                </rewrite>
            </catalog>
        </blocks>
    </global>
</config>

(3) Now Create block file of our custom module in app/code/local/Chand/Software/Block/Product/View.php

class Chand_Software_Block_Product_View extends Mage_Catalog_Block_Product_View
{
    /**
     * Put your logic here
     *
     */
}