acme-get-post-ids-array.php

<?php
/**
 * Get array of post ID's with specific meta key and value
 * 
 * @param string $meta_key   - The meta key you are checking for
 * @param string $meta_value - The meta value for the meta key you're checking for
 * @param string $post_type  - The post type to use with get_posts()  - default: post
 * 
 * @return array
 */
function acme_post_ids_array( $meta_key, $meta_value, $post_type = 'post' ) {
    // Create array.
    $post_ids = array();

    // Args for posts.
    $args = array(
        'meta_query' => array(
            array(
               'key'     => $meta_key,
               'value'   => $meta_value,
               'compare' => '='
            )
        ),
        'numberposts' => -1,
        'offset'      => 0,
        'post_type'   => $post_type,
        'post_status' => 'publish',
    );

    // Filter the args.
    $args = apply_filters( 'acme_post_ids_array_args', $args );

    // Get all posts.
    $posts = get_posts( $args );

    // Loop through posts.
    foreach( $posts as $the_post ) {
        // Add post ID to array.
        $post_ids[] = $the_post->ID;
    }

    // Filter the array.
    return apply_filters( 'acme_post_ids_array', $post_ids );
}