<?php
	
/**
 * Plugin Name: My Plugin
 * Description: Description of the plugin (140 characters)
 * Plugin URI:  URL to info about plugin 
 * Author URI:  https://wp-kama.com
 * Author:      Kama
 *
 * Text Domain: Translation ID. E.g. my-plugin
 * Domain Path: Path to MO file (relative to plugin folder)
 *
 * Requires PHP: 5.4
 * Requires at least: 2.5
 * 
 * License:     GPL2
 * License URI: https://www.gnu.org/licenses/gpl-2.0.html
 *
 * Network:     true - activates the plugin for the whole network
 * Version:     1.0
 */

// Plugin code starts here

• register_activation_hook()Registers the function to activate the plugin.
• register_deactivation_hook()Registers the function to deactivate the plugin.
• register_uninstall_hook()Registers the function for deleting the plugin.
•  
• plugins_url()Gets URL of plugins/mu plugins folder (no slash at the end)**.
• plugin_basename()Path to plugin file (from plugins folder).
• plugin_dir_path()Gets Path to plugin folder (has slash at the end).
• plugin_dir_url()Gets URL of the plugin folder (has slash at the end).
•  
• get_plugins()Gets data of plugins (active and inactive).
• get_plugin_data()Gets data of the plugin from file headers.
•  
• activate_plugins()Activates plugins.
• deactivate_plugins()Deactivates plugins.
• is_plugin_active()Checks if a plugin is active. Works only in the admin panel.

uninstall.php

<?php 
if( ! defined('WP_UNINSTALL_PLUGIN') ) exit;

// the check passed successfully. Starting from here remove all plugin data (options, db tables etc.).
delete_option( 'plug_option' );

• wp_register_script()Registers the js file.
• wp_enqueue_script()Registers and connects the js file.
• wp_dequeue_script()Deletes file from the output queue.
• wp_add_inline_script()Adds JS code to the registered script.
• wp_deregister_script()Unregisters the js file.
• wp_script_add_data()Adds data to the script. Example: script only for "IE 6", "lt IE 9".
• wp_localize_script()Adds data before the specified script.
• wp_script_is()Whether the file has been registered/waiting for output.
•  
• wp_register_style()Registers the css file.
• wp_enqueue_style()Registers and connects the css file.
• wp_dequeue_style()Deletes file from the output queue.
• wp_add_inline_style()Adds styles directly to the html document.
• wp_deregister_style()Unregisters the css file.
• wp_style_add_data()Adds data to styles. Example: styles only for "IE 6", "lt IE 9".
• wp_style_is()Whether the file has been registered/waiting for output.

add_action( 'wp_enqueue_scripts', 'add_my_scripts' );    // Front
add_action( 'admin_enqueue_scripts', 'add_my_scripts' ); // Admin
add_action( 'login_enqueue_scripts', 'add_my_scripts' ); // wp-login.php
function add_my_scripts(){

	if ( ! wp_script_is( 'my-script', 'enqueued' ) ) {
		// The my-script is not added to the queue
	}
	
	if ( ! wp_style_is( 'my-style', 'registered' ) ) {
		// Styles my-script is not registered
	}
	
	wp_enqueue_script( 'my-script', 'src', ['deps'], '1.0', 'in_footer' );
	wp_enqueue_style(  'my-style',  'src', ['deps'], '1.0', 'all' );
	
	wp_enqueue_style( 'theme-style', get_stylesheet_uri() ); // theme style.css
	
	wp_localize_script( 'my-script', 'myajax', [
		'ajaxurl' => admin_url( 'admin-ajax.php' )
	] );
	
	wp_script_add_data( 'my-script', 'conditional', 'lt IE 9' );
	wp_style_add_data(  'my-style',  'conditional', 'lt IE 9' )
	
	wp_add_inline_script( 'my-scripts', 'alert("Hello!");' );
	wp_add_inline_style( 'my-style', '
		.mycolor{
			background: #fff;
		}
	');
	
	wp_deregister_script( 'my-script' );
	wp_deregister_style( 'my-style' );
}

• add_action()Hangs a function on an event.
• remove_action()Deletes a function from the event.
• did_action()Gets a number of how many times the event was performed.
• do_action()Creates an event.
• do_action_ref_array()Creates an event. Arguments are passed in an array.
• has_action()Checks whether a function is hung on the event.
• current_action()Gets the name of the current event.
• doing_action()Checks if the event is being processed at the moment.
• remove_all_actions()Deletes all functions attached to the event.
•  
• add_filter()Hangs a function on a filter.
• remove_filter()Deletes a function from the filter.
• apply_filters()Creates a filter.
• apply_filters_ref_array()Creates a filter. Arguments are passed in an array.
• has_filter()Checks whether the function is hung on the filter.
• current_filter()Gets the name of the current filter.
• doing_filter()Checks if the filter is currently being processed.
• remove_all_filters()Deletes all functions attached to the filter.

function my_filter_function( $str ){
	return 'Hello '. $str;
}

// Let's attach a function to the filter
add_filter( 'my_filter', 'my_filter_function' );

// Call the filter
echo apply_filters( 'my_filter', 'John' ); //> Hello John

// Create a function for the event
function my_action_function( $text ){
	echo 'The my_action event has been triggered just now.';
}

// Let's attach the function to the my_action event
add_action( 'my_action', 'my_action_function' );

// Action call
do_action( 'my_action' ); //> The my_action event has been triggered just now.

• __()Gets string translation.
• _e()Outputs a string translation.
• _n()Gets a string translation after a number.
•  
• esc_attr__()Gets string translation + esc_attr().
• esc_attr_e()Outputs the string translation + esc_attr().
• esc_html__()Gets the string translation + esc_html().
• esc_html_e()Outputs the string translation + esc_html().
•  
• _x()Gets the string translation for context.
• _ex()Outputs the string translation for the context.
• _nx()Gets a string translation after a number for the context.
•  
• date_i18n()Gets the translated date. Localization for date().
•  
• determine_locale()Gets the locale of the site suitable for the current query.
• get_locale()Gets the locale of the site. E.g. en_US.
• get_user_locale()Gets the user's locale.
• switch_to_locale()Switches the user's locale.
• is_locale_switched()Checks if switch_to_locale() was used.
•  
• load_plugin_textdomain()Loads .mo file from plugin folder.
• load_muplugin_textdomain()Loads .mo file from plugin's MU folder.
• load_theme_textdomain()Loads the .mo file from the theme folder.
• load_child_theme_textdomain()Loads the .mo file from the child theme folder.
• load_textdomain()Loads the specified .mo file from any folder.
• is_textdomain_loaded()Checks if the .mo file is loaded.
• unload_textdomain()Unloads (removes) the loaded .mo file.

if( is_single() ){
	// single post type page
}

• wp_doing_ajax()Works for an AJAX request in WordPress.
• wp_doing_cron()Works for WordPress cron requests.
• is_ssl()Works for HTTPS (SSL).
• is_front_page()Home page.
• is_home()Posts page (or Home page).
• is_single()Page of post of any type except: attachment and page.
• is_singular()Page of post of any type.
• is_page()The page of a Static page.
• is_page_template()Whether or not a template file is used for the page.
• is_attachment()Attachment page.
• is_search()Search result page.
• is_archive()Archive page: category, tag, author, date.
• is_category()Category page.
• is_tag()Tag page.
• is_tax()Page of custom taxonomy.
• is_post_type_archive()Page of custom post type archive.
• is_author()Page of author posts archive.
• is_date()Archive page by date.
• is_year()Archive page by Year.
• is_month()Archive page by Month.
• is_day()Archive page by Day.
• is_time()Archive page by an hour, minute, second.
• is_paged()Pagination page.
• is_404()"Not found" page.
• is_preview()Post preview page.
• is_feed()Feed page.
• is_admin()Admin panel.
• is_network_admin()Administration panel "Network management" of Multisite sites.
• is_blog_admin()Section of the admin panel of a separate site in Multisite.
• is_user_admin()The "User" section of the admin panel in Multisite.
• is_customize_preview()Page of customizer in the admin area.
• is_robots()Query to the robots.txt file.
• is_embed()Page of embedding post.
• is_comment_feed()Comments feed page.
• is_trackback()Page of pings (trackback).

if( is_user_logged_in() ){
	// user is authorized
}

• is_user_logged_in()Checks if the user is logged in.
• have_comments()Checks if there are comments to be displayed on the page.
• comments_open()Checks if comments are opened.
• has_category()Checks if the post is in at least one category.
• has_tag()Checks if the post is in at least one tag.
• has_term()Checks if the post is in at least one taxonomy term.
• has_excerpt()Checks if the post has an excerpt (quote, short description).
• is_nav_menu()Checks if there is a menu by ID, slug or name.
• has_nav_menu()Checks if registered menu area have an attached menu.
• has_shortcode()Checks if content contains the specified shortcode.
• shortcode_exists()Checks if the specified shortcode is registered.
• in_category()Checks if the post are in a category.
• in_the_loop()Checks if we are inside a WP Loop.
• is_main_query()Checks if we are in the main WP Loop.
• is_active_sidebar()Checks if there is at least one widget in the widgets area.
• is_child_theme()Checks if a child theme being used.
• is_dynamic_sidebar()Checks if theme sidebars are enabled and they has at least one widget.
• is_local_attachment()Checks if the given URL is an attachment page.
• is_multisite()Checks if the multisite mode is turned on.
• is_new_day()Checks if the current date differs from the previous (in the loop).
• is_post_type_hierarchical()Checks if the post type is hierarchical (tree-like).
• is_taxonomy_hierarchical()Checks if the taxonomy is hierarchical (tree-like).
• is_sticky()Checks if the post is sticky (be shown on front page).
• pings_open()Checks if the post is allowed to receive pings.
• post_exists()Checks if there is a post with a specified title (post_title).
• taxonomy_exists()Checks if the specified taxonomy exist.
• post_password_required()Checks if the post is password protected and it is correct.
• term_exists()Checks if the taxonomy element exist (return the term ID).
• cat_is_ancestor_of()Checks if the category is child of another one (all nesting levels).
• term_is_ancestor_of()Checks if the term is child of another one (all nesting levels).
• wp_attachment_is()Checks if the attachment is an image, audio or video.
• wp_attachment_is_image()Checks if the attachment (post) is a image .
• is_header_video_active()Checks if the header video should be shown on the page.
• has_custom_header()Checks if the picture/video is set for the theme header.
• wp_is_mobile()Checks if the site is viewed on a mobile device.
• wp_is_post_autosave()Checks if the post is an auto-save.
• wp_is_post_revision()Checks if the post is a revision.

Core:

# Download WordPress 
wp core download --locale=ru_RU

# Generate wp-config.php:
wp core config --dbname=NAME --dbuser=USER --dbpass=PASS --dbprefix=wp_

# Create DB (based on wp-config.php)
wp db create

# Install WP to created DB
wp core install --url=example.com --title=Example --admin_user=supervisor \
[email protected] --admin_password=strongpassword

Post:

# List posts:
wp post list

# Edit post:
wp post edit 1

# Post update:
wp post update 1 --post_title="Your New title..."

# Create posts:
wp post create --post_status=publish --post_title="Second Post" --edit

Post meta:

# See all metas of post 18:
wp post meta list 18

# Get post meta value:
wp post meta get 18 meta_name

# Delete post meta by key:
wp post meta delete 18 meta_name

DB:

# Create DB dump
wp db export - --add-drop-table --default-character-set=utf8mb4 | gzip > ./db_backup-$(date +%Y-%m-%d-%H%M%S).sql.gz

# Insert data from DB dump to DB
wp db import db_backup-2022-01-20.sql

# Login WordPress db:
wp db cli

# Run SQL Query:
wp db query "SELECT user_login, ID FROM wp_users;"

# Optimize db:
wp db optimize

Update:

# Update WordPress
wp core update

# Update all plugins:
wp plugin update --all

Themes & Plugins

# List plugins:
wp plugin list

# Search plugin:
wp plugin search yoast

# Install plugin:
wp plugin install yoast

# List installed themes:
wp theme list

# Install theme:
wp theme install twentyone

# Activate theme:
wp theme activate twentyone