WordPressプラグインを作ってみる。はじめの一歩。

<?php
/**
 * @package Hello_Dolly
 * @version 1.7.2
 */
/*
Plugin Name: Hello Dolly
Plugin URI: http://wordpress.org/plugins/hello-dolly/
Description: This is not just a plugin, it symbolizes the hope and enthusiasm of an entire generation summed up in two words sung most famously by Louis Armstrong: Hello, Dolly. When activated you will randomly see a lyric from <cite>Hello, Dolly</cite> in the upper right of your admin screen on every page.
Author: Matt Mullenweg
Version: 1.7.2
Author URI: http://ma.tt/
*/

function hello_dolly_get_lyric() {
    /** These are the lyrics to Hello Dolly */
    $lyrics = "Hello, Dolly
Well, hello, Dolly
It's so nice to have you back where you belong
You're lookin' swell, Dolly
I can tell, Dolly
You're still glowin', you're still crowin'
You're still goin' strong
I feel the room swayin'
While the band's playin'
One of our old favorite songs from way back when
So, take her wrap, fellas
Dolly, never go away again
Hello, Dolly
Well, hello, Dolly
It's so nice to have you back where you belong
You're lookin' swell, Dolly
I can tell, Dolly
You're still glowin', you're still crowin'
You're still goin' strong
I feel the room swayin'
While the band's playin'
One of our old favorite songs from way back when
So, golly, gee, fellas
Have a little faith in me, fellas
Dolly, never go away
Promise, you'll never go away
Dolly'll never go away again";

    // Here we split it into lines.
    $lyrics = explode( "\n", $lyrics );

    // And then randomly choose a line.
    return wptexturize( $lyrics[ mt_rand( 0, count( $lyrics ) - 1 ) ] );
}

// This just echoes the chosen line, we'll position it later.
function hello_dolly() {
    $chosen = hello_dolly_get_lyric();
    $lang   = '';
    if ( 'en_' !== substr( get_user_locale(), 0, 3 ) ) {
        $lang = ' lang="en"';
    }

    printf(
        '<p id="dolly"><span class="screen-reader-text">%s </span><span dir="ltr"%s>%s</span></p>',
        __( 'Quote from Hello Dolly song, by Jerry Herman:', 'hello-dolly' ),
        $lang,
        $chosen
    );
}

// Now we set that function up to execute when the admin_notices action is called.
add_action( 'admin_notices', 'hello_dolly' );

// We need some CSS to position the paragraph.
function dolly_css() {
    echo "
    <style type='text/css'>
    #dolly {
        float: right;
        padding: 5px 10px;
        margin: 0;
        font-size: 12px;
        line-height: 1.6666;
    }
    .rtl #dolly {
        float: left;
    }
    .block-editor-page #dolly {
        display: none;
    }
    @media screen and (max-width: 782px) {
        #dolly,
        .rtl #dolly {
            float: none;
            padding-left: 0;
            padding-right: 0;
        }
    }
    </style>
    ";
}

add_action( 'admin_head', 'dolly_css' );

plugins
 ┗ plugin-name
   ┗ plugin-name.php

/**
 * Plugin Name: YOUR PLUGIN NAME
 */

plugins
 ┗ simple-customize
   ┗ simple-customize.php

<?php
/*
Plugin Name: Simple Customize
Description: This plugin cusmizes admin area.
*/

// ①管理画面の右上にメッセージを表示
function my_hello_message() {
    $words = "こんにちは。今日もいいブログ日和ですね！";
    printf(
        '<p id="message">%s</p>',
        $words
    );
}
add_action( 'admin_notices', 'my_hello_message' );

function my_message_css() {
    echo "
    <style type='text/css'>
    #message {
        float: right;
        padding: 5px 10px;
        margin: 0;
        font-size: 16px;
        line-height: 1.6666;
    }

    .block-editor-page #message {
        display: none;
    }
    @media screen and (max-width: 782px) {
        #message{
            float: none;
            padding-left: 0;
            padding-right: 0;
        }
    }
    </style>
    ";
}
add_action( 'admin_head', 'my_message_css' );

// ②管理画面上部のバーから不要なメニューをオフにする
function my_remove_adminbar_menu( $wp_admin_bar ) {
    $wp_admin_bar->remove_menu( 'wp-logo' );      // WPロゴ
    $wp_admin_bar->remove_menu( 'comments' );     // コメント
}
add_action('admin_bar_menu', 'my_remove_adminbar_menu', 101);

// ③管理画面左のバーから不要なメニューをオフにする
function my_remove_admin_menu( $wp_admin_bar ) {
    remove_menu_page( 'edit-comments.php' );          // コメント
}
add_action('admin_menu', 'my_remove_admin_menu');