Here is one of the simplest plugin.
It includes (among other things):
- variable declaration
- echo something
- css string inclusion in head
Source: https://plugins.trac.wordpress.org/browser/hello-dolly/trunk/hello.php
Quoted from:
https://developer.wordpress.org/plugins/the-basics/
<?php /** * @package Hello_Dolly * @version 1.6 */ /* Plugin Name: Hello Dolly Plugin URI: https://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: 1.6 Author URI: http://ma.tt/ Text Domain: hello-dolly */ 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 We feel the room swayin' While the band's playin' One of your old favourite songs from way back when So, take her wrap, fellas Find her an empty lap, fellas Dolly'll 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 We feel the room swayin' While the band's playin' One of your old favourite songs from way back when Golly, gee, fellas Find her a vacant knee, fellas Dolly'll never go away Dolly'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() { $chosen = hello_dolly_get_lyric(); echo "<p id='dolly'>$chosen</p>"; } // 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() { // This makes sure that the positioning is also good for right-to-left languages $x = is_rtl() ? 'left' : 'right'; echo " <style type='text/css'> #dolly { float: $x; padding-$x: 15px; padding-top: 5px; margin: 0; font-size: 11px; } </style> "; } add_action( 'admin_head', 'dolly_css' ); ?>