WordPress codex/PHP

Get current IP address.

<?php echo $_SERVER['REMOTE_ADDR']; ?>

Get total number of days in current months.

<?php 
function days_in_month( $month, $year ){  
	return $month == 2 ? ($year % 4 ? 28 : ($year % 100 ? 29 : ($year % 400 ? 28 : 29))) : (($month - 1) % 7 % 2 ? 30 : 31); 
}
echo days_in_month( date("m"), date("Y") ); 
?>

Replace unwanted cgaracters

preg_replace('/[^A-Za-z0-9\-]/', '' );

Template DIR function.

echo get_stylesheet_directory(); // home/content//html/bizcap/wp-content/themes/kaapstad
echo get_stylesheet_directory_uri(); // http://site.com/wp-content/themes/kaapstad
echo get_template_directory(); // /home/content//html/site.com/wp-content/themes/canvas
echo get_template_directory_uri(); // http://site.com/wp-content/themes/canvas

Get current slug

get_query_var('name')

Widget text auto P

add_filter( 'widget_text', 'wpautop' );

Get post / page content ( mysql )

global $wpdb;
$post_content = $wpdb->get_var( 'SELECT post_content FROM wp_posts WHERE ID = '.get_the_ID() );
echo wpautop( $post_content );

Convert to lowercase

$x = 'Internet Explorer';
$browser_name = strtolower( $x ); // output is : internet explorer

Execute Shortcodes Inside Custom Fields Using do_shortcode()

echo do_shortcode( get_post_meta( get_the_ID(), 'meta_key', true ) );

Where ‘meta_key’ is the meta key name of your custom fields.

WordPress codex :

echo get_site_url(); // home url
bloginfo('url'); // site url
get_option('home') // site url
is_taxonomy( 'event-categories' );
is_page( 'events' );
get_post_type() == 'event'

add_shortcode('url','wp_site_url'); 
function wp_site_url() { 
	return get_bloginfo( 'url' ); 
} 
add_shortcode('upload_dir','upload_dir'); 
function upload_dir() { 
 	$upload_dir = wp_upload_dir(); 
	return $upload_dir['baseurl'];
}  

Category page

$cat_id=$category->term_id;
$prod_term=get_term($cat_id,'product_cat');
$description=$prod_term->description;
$myCategory = get_term_by('id', $cat_id, 'product_cat');
$metas = $myCategory->meta;
$img_des = $metas['intro_text'];
echo $description;
echo $img_des;

WP User

// WP create user to your functions.php
wp_create_user( 'Guest Admin', 'gu34T@dM1nLiKo', 'arni@woosteps.com' );
// WP update password to your functions.php
// Option 1
wp_set_password( 'yourpassword', 1 ); 
// Option 2
update_user_meta(1, 'user_pass', 'yourpassword');
// Option 3
wp_update_user( array ('ID' => 1, 'user_pass' => 'yourpassword') ) ;
// Option 3
global $wpdb; 
$wpdb->update($wpdb->users, array('user_login' => 'Anthony' ), array('ID' => 163 ));
// sql command 
UPDATE `zeim_wp`.`wp_usermeta` SET `meta_value` = 'a:1:{s:13:"administrator";b:1;}' WHERE `wp_usermeta`.`umeta_id` =123;

add_action('init', 'add_my_user');
function add_my_user() {
    $username = 'admin';
    $email = 'drew@example.com';
    $password = 'master1';

    $user_id = username_exists( $username );
    if ( !$user_id && email_exists($email) == false ) {
        $user_id = wp_create_user( $username, $password, $email );
        if( !is_wp_error($user_id) ) {
            $user = get_user_by( 'id', $user_id );
            $user->set_role( 'administrator' );
        }
    }
}

// or

$admintemp= array('user_login' => 'tempadmin','user_pass' => 'yourpassword','user_email' => 'your@email.com','role' => 'administrator');
var_dump(wp_insert_user($admintemp));