Example of an update routine for a plugin

jorbin_update.php

<?php
/*
Plugin Name: update versioning 
Description: Example of an update routine for a plugin 
Author: Aaron Jorbin 
Version: 0.1
Author URI: http://aaron.jorb.in 
*/


add_action('admin_init', 'jorbin_update_routine');

function jorbin_update_routine(){
    $version = get_option( 'jorbin_db_version', null);

    if ( is_null($version) ) { 
        add_option('jorbin_db_version', 0, '', 'yes');
        return;
    } else {
        // Cast to integer so we can do simple comparisons
        $version = (int) $version;
    }   

    if ( $version < 1 ) { 
        jorbin_update_1();
        $new_version = 1;
    }   

    if ( $version < 2 ) { 
        jorbin_update_2();
        $new_version = 2;
    }   

    // If we updated the options, save our new version
    if ( isset($new_version) &&  $new_version !== $version ) { 
        update_option( 'jorbin_db_version', $new_version );
    } 
    
}

function jorbin_update_1(){
// update options blah blah blah

}

function jorbin_update_2(){
// update options blah blah blah

}