What does the WordPress plugin “Hello Dolly” do?

I investigated the PHP code of the “Hello Dolly” WordPress plugin to find out what it does.

What is the WordPress Plugin Hello Dolly

Hello Dolly is a plugin that comes pre-installed with WordPress, and it displays a random excerpt from the lyrics of Louis Armstrong’s song on the administration screen.

The description of the WordPress plugin is as follows:

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 Hello, Dolly in the upper right of your admin screen on every page.

Understanding the Behavior from the Source Code of “Hello Dolly”

There is only one PHP file used in “Hello Dolly.” Let’s read it to learn more about the plugin.

<?php
/**
* @package Hello_Dolly
* @version 1.6
*/
/*
Plugin Name: Hello Dolly
Plugin URI: http://wordpress.org/extend/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/
*/
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' );
?>

<?php

/**

* @package Hello_Dolly

* @version 1.6

Plugin Name: Hello Dolly

Plugin URI: http://wordpress.org/extend/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/

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 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 "

#dolly {

float: $x;

padding-$x: 15px;

padding-top: 5px;

margin: 0;

font-size: 11px;

}

</style>

}

add_action( 'admin_head', 'dolly_css' );

The beginning of the file contains comments with Plugin Name, Plugin URI, Description, Author, Version, and Author URI. At least Plugin Name is required for the plugin.

Within this file, there are three functions: hello_dolly_get_lyric, hello_dolly, and dolly_css.

hello_dolly_get_lyric

This function selects and returns one line from the lyrics of “Hello Dolly.” It uses mt_rand to get a random index. The function wptexturize is used to format the text according to WordPress standards and is still available in WordPress 5.

The lyrics contain the line “Dolly’ll never go away” twice, and there are other duplicate lines as well. While mt_rand outputs a random line, it does not remove duplicates, so those duplicate lines have a higher chance of being selected.

hello_dolly

This function retrieves one line from hello_dolly_get_lyric, converts it into HTML, and displays it. The returned HTML is shown on WordPress pages within a p tag with an id attribute of dolly.

hello_css

This function displays the CSS applied to the displayed message as the content of the style tag. The function is_rtl determines whether the language used is right-to-left or left-to-right, adjusting the display accordingly.

In addition to these function definitions, two actions are added within the file.

add_action('admin_notices', 'hello_dolly');: This specifies that the hello_dolly function should be executed on the action event admin_notice. The admin_notice refers to the timing of displaying notifications in the admin area, including messages such as “Plugin activated.”
add_action('admin_head', 'dolly_css');: This specifies that the dolly_css function should be executed on the action event admin_head. The admin_head is an event that occurs during the generation of the head tag when opening the admin area, and any text output here will be placed inside the head tag.

Extending the Plugin

Now that we understand how to use a simple plugin, let’s think about modifying the code to create a new plugin.

For instance, it would be interesting to display messages from “Mai-ni-chi, Shuzo! Kokoro o genki ni suru honki no ouen messeiji” based on the current date.

To obtain the date in PHP, you can use the following code to get the date in the Tokyo timezone.

$dateTime = new DateTime();
$dateTime->setTimeZone(new DateTimeZone('Asia/Tokyo'));
$year   = (int) $dateTime->format('Y');
$month  = (int) $dateTime->format('m');
$day    = (int) $dateTime->format('d');
$hour   = (int) $dateTime->format('H');
$minute = (int) $dateTime->format('i');
$second = (int) $dateTime->format('s');