We looked a little bit before at the do_action function.

What this does is execute where in the code you want a hook to take place.

We have do_action,

which can take the hook as well as arguments you want passed to it.

do_action can take multiple hooks.

Or there's the function do action reference array, which will take the hook

and then all of the extra hooks passed as a single array into one argument.

If we take a look at do_action_example,

we could see a couple things are going on here.

First, we create a function called custom_footer that all

it has in it is something called do_action.

Then, in our template code, we would cut this out, come into our

index, and paste in our custom_footer function.

So now in our template, if we call this, then this code will run.

So, let's go ahead and comment out the rest down here and run just this.

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We could see that we're getting an error in the page here, so

we have to come back into our functions.php and

set up do_action_example so that that function will be defined.

So, in our index, we're echoing out the custom_footer here and we could even put

just an hr or something to demonstrate that we are seeing what's on the page.

There's just nothing there yet.

If we come back into our code now though and we say, add_action, my_footer.

So, meaning what we defined, we set up by saying do_action here,

we created a new action hook.

And here we're saying, okay, we want to tie into my_footer action hook with

our custom function that's going to echo out this code.

If we come now and look at it,

we could see that the Custom footer text appears here.

If we wrote our code in this way, this would allow somebody else to

easily extend, or overwrite, or change whatever that code was originally.

If we look back to do_action though, and we compare it with apply_filters, we could

see one difference is that when we run apply_filters, it takes a default value.

This is because WordPress needs to have some value passed into it

that can then be modified and outputted.

That's how filters work.

However, with actions, we're simply giving them the opportunity to

run whatever code it is that they need to run.

And by default, there is no default action or set value with the do_action function.

If you find yourself in a place where you're writing a plugin or

theme that you want other people to be able to hook into and

add actions, that it's important that you add this do_action code at

the proper places in your site or in your plugin and then document that.

For example, you may be building a plugin that could have additional

functionality added to it.

However, at the time you don't want to be coding it, and you feel

maybe somebody else could integrate with your plugin to get it to work.

By providing the correct actions and filters, somebody else could easily extend

your plugin so that you don't have to do all the work in the first place.

However, their job would not be possible if

you didn't have the do_action as well as the add_filter in the correct place.