The is_singular() WordPress PHP function determines whether the query is for an existing single post of any post type (post, attachment, page, custom post types).
Usage
is_singular($post_types);
Parameters
$post_types(string|string[]|null) (Optional) – Post type or array of post types to check against. Default:''.
More information
See WordPress Developer Resources: is_singular()
Examples
Check if viewing a regular post
if (is_singular('post')) {
// Your code here...
}
Check if viewing a custom post type ‘book’
if (is_singular('book')) {
// Your code here...
}
Check if viewing a post of either custom post types ‘newspaper’ or ‘book’
if (is_singular(array('newspaper', 'book'))) {
// Your code here...
}
Display different sidebar ads based on singular pages
if (is_singular()) {
// Show ad #1
} else {
// Show ad #2
}
Add a custom function to the ‘loop_start’ action hook
add_action('loop_start', 'your_function');
function your_function() {
if (is_singular()) {
echo 'Hello World';
}
}