// Hide WordPress Update Nag to All But Admins
function hide_update_notice_to_all_but_admin() {
	if ( !current_user_can( 'update_core' ) ) {
		remove_action( 'admin_notices', 'update_nag', 3 );
	}
}
add_action( 'admin_head', 'hide_update_notice_to_all_but_admin', 1 );

// Create Proper WordPress Titles
add_theme_support( 'title-tag' );

// Create Custom WordPress Dashboard Widget
function dashboard_widget_function() {
	echo '
		<h2>Custom Dashboard Widget</h2>
		<p>Custom content here</p>
	';
}

function add_dashboard_widgets() {
	wp_add_dashboard_widget( 'custom_dashboard_widget', 'Custom Dashoard Widget', 'dashboard_widget_function' );
}
add_action( 'wp_dashboard_setup', 'add_dashboard_widgets' );

// Remove All Dashboard Widgets
function remove_dashboard_widgets() {
    global $wp_meta_boxes;
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_quick_press'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_incoming_links'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_right_now'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_plugins'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_recent_drafts'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_recent_comments'] );
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_primary'] );
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_secondary'] );
  remove_meta_box( 'dashboard_activity', 'dashboard', 'normal' );
}
add_action( 'wp_dashboard_setup', 'remove_dashboard_widgets' );

// Insert Custom Login Logo
function custom_login_logo() {
    echo '
    	<style>
        .login h1 a { background-image: url(image.jpg) !important; background-size: 234px 67px; width:234px; height:67px; display:block; }
    	</style>
    ';
}
add_action( 'login_head', 'custom_login_logo' );

// Modify Admin Footer Text
function modify_footer() {
  echo 'Created by <a href="mailto:[email protected]">you</a>.';
}
add_filter( 'admin_footer_text', 'modify_footer' );

// Enqueue Styles and Scripts
function custom_scripts() {
	wp_enqueue_style( 'bootstrap', get_template_directory_uri() . '/css/bootstrap.min.css', array(), '3.3.6' );
	wp_enqueue_style( 'style', get_template_directory_uri() . '/css/style.css' );
	wp_enqueue_script( 'bootstrap', get_template_directory_uri() . '/js/bootstrap.min.js', array('jquery'), '3.3.6', true );
	wp_enqueue_script( 'script', get_template_directory_uri() . '/js/script.js' );
}

add_action( 'wp_enqueue_scripts', 'custom_scripts' );

// Enqueue Google Fonts
function google_fonts() {
				wp_register_style( 'OpenSans', 'http://fonts.googleapis.com/css?family=Open+Sans:400,600,700,800' );
				wp_enqueue_style( 'OpenSans' );
		}

add_action( 'wp_print_styles', 'google_fonts' );

// Modify Excerpt Length
function custom_excerpt_length( $length ) {
	return 25;
}
add_filter( 'excerpt_length', 'custom_excerpt_length', 999 );

// Change Read More Link
function custom_read_more_link() {
	return '<a href="' . get_permalink() . '">Read More</a>';
}
add_filter( 'the_content_more_link', 'custom_read_more_link' );

// Change More Excerpt
function custom_more_excerpt( $more ) {
	return '...';
}
add_filter( 'excerpt_more', 'custom_more_excerpt' );

// Disable Emoji Mess
function disable_wp_emojicons() {
  remove_action( 'admin_print_styles', 'print_emoji_styles' );
  remove_action( 'wp_head', 'print_emoji_detection_script', 7 );
  remove_action( 'admin_print_scripts', 'print_emoji_detection_script' );
  remove_action( 'wp_print_styles', 'print_emoji_styles' );
  remove_filter( 'wp_mail', 'wp_staticize_emoji_for_email' );
  remove_filter( 'the_content_feed', 'wp_staticize_emoji' );
  remove_filter( 'comment_text_rss', 'wp_staticize_emoji' );
  add_filter( 'tiny_mce_plugins', 'disable_emojicons_tinymce' );
}
add_action( 'init', 'disable_wp_emojicons' );
function disable_emojicons_tinymce( $plugins ) {
  if ( is_array( $plugins ) ) {
    return array_diff( $plugins, array( 'wpemoji' ) );
  } else {
    return array();
  }
}

// Removes from admin menu
add_action( 'admin_menu', 'my_remove_admin_menus' );
function my_remove_admin_menus() {
  remove_menu_page( 'edit-comments.php' );
}
// Removes from post and pages
add_action( 'init', 'remove_comment_support', 100 );
function remove_comment_support() {
  remove_post_type_support( 'post', 'comments' );
  remove_post_type_support( 'page', 'comments' );
}
// Removes from admin bar
function mytheme_admin_bar_render() {
  global $wp_admin_bar;
  $wp_admin_bar->remove_menu( 'comments' );
}
add_action( 'wp_before_admin_bar_render', 'mytheme_admin_bar_render' );

// Change Media Gallery URL
update_option( 'upload_url_path', 'http://s3.website.com/wp-content/uploads' );

// Add 250 x 250 Custom Thumbnail Size
add_image_size( 'custom-thumbnail', 250, 250, true );

<?php $thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'custom-thumbnail' );

echo $thumb[0]; ?>

// Add Categories for Attachments
function add_categories_for_attachments() {
	register_taxonomy_for_object_type( 'category', 'attachment' );
}
add_action( 'init' , 'add_categories_for_attachments' );

// Add Tags for Attachments
function add_tags_for_attachments() {
	register_taxonomy_for_object_type( 'post_tag', 'attachment' );
}
add_action( 'init' , 'add_tags_for_attachments' );

// Add Custom Excerpt to Pages
function add_page_excerpt() {
	add_post_type_support( 'page', array( 'excerpt' ) );
}
add_action( 'init', 'add_page_excerpt' );

// Create a Global String
function global_string() {
     return 'String';
}

<?php echo global_string(); ?>

// Support Featured Images
add_theme_support( 'post-thumbnails' );

// Support Search Form
add_theme_support( 'html5', array( 'search-form' ) );

// Excluding pages from search
function exclude_pages_from_search() {
    global $wp_post_types;
    $wp_post_types['page']->exclude_from_search = true;
}
add_action( 'init', 'exclude_pages_from_search' );

// Disable XML RPC
add_filter( 'xmlrpc_enabled', '__return_false' );
remove_action( 'wp_head', 'rsd_link' );
remove_action( 'wp_head', 'wlwmanifest_link' );

// Escape HTML in <code> or <pre><code> tags.
function escapeHTML($arr) {

	if (version_compare(PHP_VERSION, '5.2.3') >= 0) {

		$output = htmlspecialchars($arr[2], ENT_NOQUOTES, get_bloginfo('charset'), false);
	}
	else {
		$specialChars = array(
            '&' => '&amp;',
            '<' => '&lt;',
            '>' => '&gt;'
		);

		// decode already converted data
		$data = htmlspecialchars_decode( $arr[2] );
		// escapse all data inside <pre>
		$output = strtr( $data, $specialChars );
	}
	if (! empty($output)) {
		return  $arr[1] . $output . $arr[3];
	}	else 	{
		return  $arr[1] . $arr[2] . $arr[3];
	}
}
function filterCode($data) { // Uncomment if you want to escape anything within a <pre> tag
	//$modifiedData = preg_replace_callback( '@(<pre.*>)(.*)(<\/pre>)@isU', 'escapeHTML', $data );
	$modifiedData = preg_replace_callback( '@(<code.*>)(.*)(<\/code>)@isU', 'escapeHTML', $data );
	$modifiedData = preg_replace_callback( '@(<tt.*>)(.*)(<\/tt>)@isU', 'escapeHTML', $modifiedData );

	return $modifiedData;
}
add_filter( 'content_save_pre', 'filterCode', 9 );
add_filter( 'excerpt_save_pre', 'filterCode', 9 );

// Create Custom Global Settings
function custom_settings_page() { ?>
  <div class="wrap">
	<h1>Custom Settings</h1>
	<form method="post" action="options.php">
	   <?php
	       settings_fields( 'section' );
	       do_settings_sections( 'theme-options' );      
	       submit_button();
	   ?>          
	</form>
  </div>
<?php }

function custom_settings_add_menu() {
  add_menu_page( 'Custom Settings', 'Custom Settings', 'manage_options', 'custom-settings', 'custom_settings_page', null, 99 );
}
add_action( 'admin_menu', 'custom_settings_add_menu' );

// Example setting
function setting_twitter() { ?>
  <input type="text" name="twitter" id="twitter" value="<?php echo get_option('twitter'); ?>" />
<?php }

function custom_settings_page_setup() {
	add_settings_section( 'section', 'All Settings', null, 'theme-options' );
	add_settings_field( 'twitter', 'Twitter Username', 'setting_twitter', 'theme-options', 'section' );
  register_setting( 'section', 'twitter' );
}
add_action( 'admin_init', 'custom_settings_page_setup' );

<?php echo get_option( 'twitter' ); ?>

function remove_admin_bar() {
	remove_action( 'wp_head', '_admin_bar_bump_cb' );
}
add_action( 'get_header', 'remove_admin_bar' );