I'm experimenting with creating a function to write code into htaccess (I understand the security issues associated). I'm currently using the function insert_with_markers() as a starting point however its throwing a 'call to undefined function' error.

I am using it within a function that is only running whilst logged into the Admin Dashboard.

I understand that the function if found in the file: wp-admin/includes/misc.php but I made the assumption that this file is loaded whilst within the Admin Dashboard anyway, so I don't need to include it?

If I manually include the file, the function runs correctly.

My question is: does the wp-admin/includes/misc.php file not get loaded by default when logged in to the Dashboard? Or is it only loaded in certain cirumstances?

2 Answers 2


Looks like insert_with_markers() function becomes available during admin_init hook. So in order for your code to work, you should do the following:

function do_my_htaccess_stuff_371705() {
//function `insert_with_markers()` is working now

add_action('admin_init', 'do_my_htaccess_stuff_371705');
  • 1
    Can confirm - this solved the issue for me. I redesigned to code to let the add_action trigger my function and it allowed me to remove the include. Thanks very much!
    – t2pe
    Commented Jul 24, 2020 at 14:59

By looking at the source of the latest version, it shows that misc.php only gets included in one place at wp-admin/includes/admin.php. The include there is unconditional. That file in turn gets included seemingly unconditionally in wp-admin/admin.php, and this is required unconditionally as the first line in wp-admin/index.php.

So it appears that it should be the case that's always available in the admin dashboard. If it's not, I'd suggest looking in more detail at what happens in wp-admin/admin.php in case something is going on there which bails out early.

EDIT: Note that PHP gives you the require_once() command which means that it's safe to include the file using require_once more than once, so you don't lose or risk anything going wrong by putting a require_once to that file in your code.

  • 1
    See above answer that worked for me but I appreciate the detail in your response, and I always overlook require_once function so that was a good reminder. Thank you!
    – t2pe
    Commented Jul 24, 2020 at 15:00

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