How to inject html to every page with a plugin?

Question

I would like to write a plugin which injects specific content to every non admin page. This is my first plugin.

I've figured out how can I inject content to every non admin page's head:

<?php
    function myfunction() {
?>
<!-- My injected content.... -->
....
<?php
}

if (!is_admin()) {
  add_action('wp_head', 'myfunction');
}

Unfortunately I can not figure out how to inject to the body, say an element, because I did not find the appropriate action.

• Injecting a script to head, which injects elements to DOM is not a solution this case, because the injected content must be there at load time, so it may be late to modify the DOM after load.
• The injected content must be "calculated" and the only place it can be calculated is php serverside.

Answer 1

You can use the is_page() function or is_single() function to echo content to front end pages

function add_content_to_page {

if ( is_page() ) {
echo '<p>content</p>';
 }   
}

or combine the two :

function add_content_to_page {

if ( is_page() || is_single() ) {
echo '<p>content</p>';
 }   
}

Similarly you can do is_page(41) to target a specific page id or is_home() || is_front_page() to target the homepage alone there a lot more options and examples in the WordPress codex