How to stop filter from running on the index.php page?

Question

I'm trying to make a Wordpress function and currently I have this in my functions.php file:

 function find_my_image($content) {
     if(is_single()) {

    if (preg_match('#(<img.*?>)#', $content, $result)){

        $content .= '<p>Image has been found</p>';

    }
    else{

        $content .= '<p>Sorry, no image here!</p>';

    }

return $content;

 }
 }

add_filter('the_content', 'find_my_image');

The function works perfectly on a single post page, but my index.php is now blank (only the titles of the posts are displayed, but no post content). I tried removing:

add_filter('the_content', 'find_my_image');

from function.php, but that's stops the function from executing on my single.php. Also I tried using this (I don't know if it's correct):

 if(is_single()) {

     add_filter('the_content', 'find_my_image');

}

But that's just cancels the function on single.php. My guess is that add_filter('the_content', 'find_my_image'); is the problem here, but I can't figure it out, so can anyone help me out a bit?

Answer 1

You need to return content from filter function.

function find_my_image( $content ) {
    if( is_single() ) {
        if ( preg_match('#(<img.*?>)#', $content, $result ) ){
            $content .= '<p>Image has been found</p>';
        }
        else{
            $content .= '<p>Sorry, no image here!</p>';
        }
    }
    return $content;
}

add_filter( 'the_content', 'find_my_image' );