You’ll have to use add_shortcode
to achieve this. Let’s say that you want this shortcode to be called “my_cf”:
function my_cf_shortcode_callback( $atts ) {
$atts = shortcode_atts( array(
'post_id' => get_the_ID(),
), $atts, 'my_cf' );
return get_post_meta( $atts['post_id'], <FIELD_NAME>, true );
}
add_shortcode( 'my_cf', 'my_cf_shortcode_callback' );
Now you can use it by putting [my_cf]
or [my_cf post_id=POST_ID]
to your posts.