PHP

Also see:
Minimal WordPress CSS plugin example
Minimal WordPress Shortcode plugin example

This plugin adds a static Javascript .js file to WordPress which is loaded in the client.

First, create a directory for your plugin in wp-content/plugins/, e.g. wp-content/plugins/my-js-plugin

Save the following code as functions.php in the plugin folder, e.g. wp-content/plugins/my-js-plugin/functions.php

<?php
/*
Plugin Name: My JS plugin
*/

function my_plugin_enqueue_js(){
    wp_enqueue_script('my-plugin-js', plugins_url('/script.js', __FILE__), false, '1.0.0', 'all');
}
add_action('wp_enqueue_scripts', "my_plugin_enqueue_js");

Next, save your desired JS file in script.js in the plugin folder, e.g. wp-content/plugins/my-js-plugin/script.js. Example script:

jQuery(document).ready(function() {
    console.info("Your JS plugin works!");
});

Now activate your plugin your WordPress admin area.

Your Javascript will be loaded on each WordPress page until you deactivate the plugin.

Note that if you are using a JS-optimizing plugin like Autoptimize, you might not actually see your JS file as separately loaded script file as it is compiled into the single Autoptimize JS. You javascript will still be loaded on the client!

Also see:
Minimal WordPress JS plugin example
Minimal WordPress Shortcode plugin example

This plugin adds a static CSS file to WordPress.

First, create a directory for your plugin in wp-content/plugins/, e.g. wp-content/plugins/my-css-plugin

Save the following code as functions.php in the plugin folder, e.g. wp-content/plugins/my-css-plugin/functions.php

<?php
/*
Plugin Name: My CSS plugin
*/

function my_plugin_enqueue_css(){
    wp_enqueue_style('my-plugin-stylesheet', plugins_url('/style.css', __FILE__), false, '1.0.0', 'all');
}
add_action('wp_enqueue_scripts', "my_plugin_enqueue_css");

Next, save your desired CSS file in style.css in the plugin folder, e.g. wp-content/plugins/my-css-plugin/style.css. Example for a stylesheet:

/* This is just an example CSS and does not have any specific meaning! */
.my-plugin-class {
    font-weight: bold;
}

Now activate your plugin your WordPress admin area.

Your CSS will be loaded for each WordPress page until you deactivate the plugin.

Note that if you are using a CSS-optimizing plugin like Autoptimize, you might not actually see your CSS file as separately loaded stylesheet as it is compiled into the single Autoptimize CSS. You style will still be loaded!

Also see:
Minimal WordPress JS plugin example
Minimal WordPress CSS plugin example

This plugin creates a simple (static – no parameters) shortcode in WordPress

First, create a directory for your plugin in wp-content/plugins/, e.g. wp-content/plugins/my-shortcode-plugin

Save the following code as functions.php in the plugin folder, e.g. wp-content/plugins/my-shortcode-plugin/functions.php

<?php 
/*
Plugin Name: My shortcode plugin
*/

function my_shortcode( $atts , $content = null ) {
   return '<h2>Shortcode works</h2>';
}
 
add_shortcode( 'my-shortcode', 'my_shortcode' );

Now activate your plugin your WordPress admin area.

You can now create a post or page containing this code:

[my-shortcode][/my-shortcode]

which will be rendered like this:

Shortcode works

Also see:
Minimal WordPress JS plugin example
Minimal WordPress CSS plugin example
Minimal WordPress Shortcode plugin example

This is the minimal wordpress plugin – it does not do anything at all, but you can activate it and use it as a basis for your plugins.

First, create a directory for your plugin in wp-content/plugins/, e.g. wp-content/plugins/my-plugin

Save the following code as functions.php in the plugin folder, e.g. wp-content/plugins/my-plugin/functions.php

<?php 
/*
Plugin Name: My plugin
*/

Now you can activate your plugin your WordPress admin area:

The WordPress function the_date() and get_the_date() always return the date / time in the locale format defined by the language setting of the current WordPress installation.

What if you need to get the date in a specific locale, e.g. english?

Setting the wordpress language to the target locale will successfully achieve this, but will also change the language of other parts of WordPress and is therefore often not an option.

In case you can’t do that and you have to find a programmatic solution, this is my way to force

<?php the_date('r', '', '', TRUE); ?>

to a specific locale ("C" i.e. plain english in this case)

<?php
    setlocale(LC_TIME, "C"); // Set to target locale (in which you want the date to be formatted
    echo strftime("%a, %d %b %Y %H:%M:%S %z", get_post_time('U', TRUE)); // Parse wordpress time and format it again
    setlocale(LC_TIME, "de_DE"); // Set back to the original locale!
?>

Since the_date() ignores setlocale() calls, we use PHP’s strftime() to work around this.

First, we set the target tocale (the locale for the date to be formatted in) using setlocale(LC_TIME, "C"); Replace "C" by your target locale! "C" is a good choice if you want plain english.

Then, we get the post date & time (the same date & time that is used / returned by the_date() & get_the_date()) using get_post_time('U', TRUE); . "U" means return as Unix timestamp. TRUE is very important here since it tells get_post_time() to return the timestamp as UTC. If you don’t use TRUE here, your dates will be offset by several hours (depending on your timezone) in case they are not UTC already.

After that, we run strftime() to format the timestamp. You need to insert your desired format string here. In my case, the format string is "%a, %d %b %Y %H:%M:%S %z" which is a RFC2822 date. Note that using this method, the timezone (%z) will always be +0000 since it’s formatted as a UTC date. However, the timezone offset will be correctly accounted for.

As a last step, we re-set the original locale using setlocale(LC_TIME, "de_DE"); . This avoids affecting other function, e.g. in other plugins. You need to insert the correct (original) locale here. In my case, I know the correct locale is "de_DE", but in your case this may differ.

Problem:

You are writing a wordpress plugin in which you need the path to the wp-content directory on the filesystem.

Solution:

Use the WP_CONTENT_DIR constant.

$path_to_wp_content = WP_CONTENT_DIR; // e.g. "/var/sites/techoverflow.net/wp-content"

Note that WP_CONTENT_DIR has no trailing slash.

Use WP_CONTENT_DIR . "/" like this

$path_to_wp_content = WP_CONTENT_DIR . "/"; // e.g. "/var/sites/techoverflow.net/wp-content/"

to get the path to wp_content including a trailing slash.

Problem:

In your custom WordPress plugin or theme you have code like

$query = new WP_Query( );
while ( $query->have_posts() ) {
        $query->the_post();
        // ... your code to process the post ...
}

But $query->have_posts() is always false and the loop is never executed.

Solution:

WP_Query works only if you use an appropriate query. Using no query at all is not equivalent to list all posts!

This is likely what you want to do:

$query = new WP_Query(array('post_type' => 'post'));

There are well-documented solutions to recover the wordpress admin access if you have MySQL, phpMyAdmin or shell access.

This solution shows you how to create a new admin user if you don’t know the admin username or password and you don’t have any form of MySQL or shell access (only FTP access is required).

Step 1: Identify your currently active theme

This can be done by looking at the source code of your homepage (go to your domain, then Ctrl+U to show the source) and then Ctrl+F-search for wp-content/themes. It will show hits like https://mydomain.de/wp-content/themes/twentyfifteen/style.css. This means the currently active theme is twentyfifteen.

Step 2: Create a new admin user using functions.php

Now open your FTP software (I recommend FileZilla) and find your wp-content folder. Inside wp-content, go to themes and then open the folder of your currently active theme.

If the currently active theme is not listed in your wp-content/themes folder, you might have the wrong wp-content folder. Check if there are any other folders around.

When you have found your theme folder, edit functions.php and, just after the first <?php, add this block of code:

function wpb_admin_account(){
    $user = 'newadmin';
    $pass = 'saiquae9shahZus6eeri3feNae8gie';
    $email = 'admin-email@example.org';
    if ( !username_exists( $user )  && !email_exists( $email ) ) {
        $user_id = wp_create_user( $user, $pass, $email );
        $user = new WP_User( $user_id );
        $user->set_role( 'administrator' );
    }
}
add_action('init','wpb_admin_account');

Be sure to replace the username, password and email! I recommend to use a new random password and a non-generic username! The username you enter here must.

Save the file and upload it to the server.

After that, goto your homepage and reload once (this will create the new user).

Then, try to login using your newly created user (go to e.g. https://my-domain.com/wp-admin to do so!). If it doesn’t work, check if you edited the functions.php for the correct theme and try to use a different username!

Step 3: Delete the code we just created

If you just leave in the code, this will create a potential security risk. So I recommend deleting it right away!

Also, be sure to delete any admin users you don’t need afterwards.