Plugin Development 101 - What Makes a Plugin?

This entry is part 2 of 14 in the Plugin Development 101 Series

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In this first real part of the Plugin Development 101 tutorial series we look into what makes a plugin. How is a plugin different than any other .php file? How do you make WordPress recognize your code as a plugin?

A plugin in WordPress is really nothing more than a PHP file (or multiple PHP files) with a very specific piece of information included at the top of the file that has been placed in the wp-content/plugins/ folder.

There is no minimum or maximum for what a plugin can or must do. Plugins can be a single line of code, or 50,000 lines of code. Regardless of the size of a plugin, it is defined as a plugin in exactly the same way: by a piece of meta data placed in the main file.

At the top of every WordPress plugin is a comment block that contains information about the plugin:

The name of the plugin
A brief description of the plugin
The URL of the plugin’s homepage
The author of the plugin
The author’s website
The plugin version number

The meta data is always placed in a comment block, so like:

<?php
/*
Plugin Name: Featured Comments
Plugin URI: https://pippinsplugins.com/featured-comments
Description: Lets the admin add "featured" or "buried" css class to selected comments. Handy to highlight comments that add value to your post. Also includes a Featured Comments widget
Version: 1.2.1
Author: Pippin Williamson
Author URI: https://pippinsplugins.com
*/

All but the Plugin name lines are optional. A plugin can be defined with just this:

<?php
/*
Plugin Name: Featured Comments
*/

This comment block should only ever be placed in the main plugin file, if your plugin has more than one.

The simple presence of this code block is all that is needed for WordPress to recognize your code as a plugin.

We will go into how to organize your plugin code in one of the upcoming parts of this series, for now just remember that a plugin is nothing more than a .php file placed inside of wp-content/plugins that contains the comment block shown above.

softmachine
June 8, 2013

Is it me or does this video not work…?
- Pippin
  June 9, 2013
  
  Works just fine for me. What browser are you on?
Wade Spane
July 7, 2013

This vid ain’t playing on my ipad at least Crome or safari . First in series was fine.
- Pippin
  July 7, 2013
  
  Does it just load forever or give some kind of error?
Wade Spane
July 7, 2013

The video container itself is there but on all the vids past the first one the vid container itself is really small and when you hit play it “media source loading has failed”. Back on my Mac everyhting is cool but iPad in Chrome and Safari same thing. iPad and apps all fully up to date.
Wade Spane
July 7, 2013

I got this message “Warning: explode() expects parameter 2 to be string, array given in /nas/wp/www/cluster-1583/pippinsplugins/wp-content/plugins/restrict-content-pro/includes/shortcodes.php on line 27” on those pages as well, Ive never checked out your restrict content plugin
Dont know if that or just getting my membership yesterday has anything to do with it.
- Pippin
  July 8, 2013
  
  I’m aware of the issue. The site is running a beta version of the plugin. It will be fixed as soon as the update is finished.
Oliver Juhas
July 8, 2013

Copy the Wade’s PHP warning. I’ve got it displayed too.

And the video just loads forever, but never actually play. I’ve checked console and no error in there. Any help on this? (Using Chrome on Win7)
Oliver Juhas
July 8, 2013

The same story with video on Opera. On FireFox 21.0 even the play button doesn’t disappear – actually pressing it seems to be doing nothing…
- Pippin
  July 8, 2013
  
  Just this video or all of them?
- Oliver Juhas
  July 8, 2013
  
  I’ve tried now this way: I’ve opened all the parts of this series in new tab and let it be for a couple of minutes. Some videos are being loaded. I am on fairly slow internet connection, but I don’t have such delays on YouTube or Vimeo (I understand I can’t compare 😉 ). Just to let you know that loading is very slow.
- Pippin
  July 8, 2013
  
  Ok thanks. I’m considering moving the videos to Vimeo (or similar service).
Filip Leemans
July 31, 2013

I want to learn how to make plugins in WordPress, so I am looking forward to reading the series.I’m logged in but can not see the video’s and at the end of the article I get the message to login to see the rest.
I tried other subscriber only articles and some of them I can see just fine. I’m using FF.
- Pippin
  July 31, 2013
  
  What is your username?
- Filip Leemans
  August 1, 2013
  
  My username is filip.leemans.
  
  I can see Pippin’s logo but have no videa controls.
- Pippin
  August 1, 2013
  
  Sorry for the trouble. I’ve found the issue and fixed it.
- Filip Leemans
  August 2, 2013
  
  Thanks
- Filip Leemans
  August 2, 2013
  
  It looks like I still have the same problem. I can’t play the video’s when I am logged in.
  I don’t know if it has anything to do with it but the first times I changed pages on the site I got following message:
  blockUI requires jQuery v1.2.3 or later! You are using v1.10.2
  
  Hope you can find what the error is.
- Pippin
  August 2, 2013
  
  Do you still see the error about needing to have an active subscription?
  
  The BlockUI error was caused by WP 3.6 and should be resolved now (cached if not).
- Filip Leemans
  August 5, 2013
  
  No, I am not asked to login or register anymore. I can see the whole articles now.
  But I still can not see the video’s, just your logo when i am logged in.
- Pippin
  August 5, 2013
  
  I will look into it. Sorry for the trouble.
- Filip Leemans
  August 6, 2013
  
  Also for the video I am not asked to log in, so that is OK. The logo and the play icon is shown but when I click it nothing happens. Also right mouse button doesn’t do anything. I tried FF and IE.
- Pippin
  August 6, 2013
  
  IT doesn’t do anything when logged in or when logged out?
- Filip Leemans
  August 7, 2013
  
  I am logged in and can see the article but when I click on the play icon nothing happens.
  
  I took a screenshot with html code: http://screencloud.net/v/bhGG
- Pippin
  August 7, 2013
  
  Does Chrome work?
  
  I can’t seem to replicate the problem . . .
- Filip Leemans
  August 8, 2013
  
  I installed Chrome and everything works.
  
  So with Chrome I have no problems and I can also watch the video’s.
  
  Thanks.
- Pippin
  August 8, 2013
  
  That’s good to know! I’ll look into FireFox and the other browsers.
mainaPlus
September 25, 2013

Hey Pippin, very good info. I’m starting to learn Plugin dev and I’m glad I found your tutorials because I know all your stuff are quality!

However I seem to be having real issues with the video, just like others have stated in their comments. My internet is pretty fast, so I know that’s not the issue. I’m guessing it’s the video player you’re using. The looooong delays are ruining the whole experience and as well as your brand 🙁
- Pippin
  September 25, 2013
  
  I’m trying to get the videos moved over to a better system really soon, sorry for the trouble.
jaredksmith
February 17, 2014

I love your tutorial style. I’m an experienced WordPress user, but haven’t done an development. The biggest problem with most tutorials is that they forget that when starting anything new, you have no idea what is important and what is not.

The way you clearly break down everything from the beginning into simple steps and show how each thing you do changes inside WordPress, really makes things clear.

Thanks for these great tutorials. I look forward to the rest of them.
- Pippin
  February 17, 2014
  
  Glad to hear it!

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Plugin Development 101 – What Makes a Plugin?

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