从函数返回字符串

So I have a function in functions.php and I want to call it in other parts of my wordpress site with shortcode, but the problem is that I don't know how to save results of my function into a variable. If anyone can help me I would be very grateful. This is the php code:

    <?php
    function get_slider() {
            $args = array(
            'post_type'     => 'something',
                    );
                    $posts = get_posts($args);
                    echo $posts;
                    if( $posts ): ?>
                    <div class="custom-posts-grid">
                    <?php foreach($posts as $post): setup_postdata( $post ); ?>
                        <?php if( have_rows('poslovna_darila') ): ?>
                            <?php while( have_rows('poslovna_darila') ): the_row(); ?>
                                <div class="slider_slick">
                                <?php // vars
                                $image = get_sub_field('thumbnail_for_poslovna_darila');
                                $link = get_sub_field('url_poslovna_darila');
                                $count = count($posts);                         
                                ?>      
                                <div class="slide">
                                    <a href="<?php echo $link; ?>">
                                    <img src="<?php echo $image['url']; ?>" alt="<?php echo $image['alt'] ?>" class="image-overlay-post" />
                                    </a>
                                </div>
                                </div>
                            <?php endwhile; ?>
                        <?php endif; ?>                         
                    <?php endforeach; ?>
                    <?php wp_reset_postdata(); ?>
                    <?php endif;
        }

            add_shortcode ('slick_slider' , 'get_slider'); ?>

The code returns array, but I need to get a value out of it or if it's possible the slider.

You can use an output buffer to return the string in your shortcode.

 <?php
function get_slider() {
    $args = array(
        'post_type'     => 'something',
    );

    $posts = get_posts($args);

    //echo $posts;

    ob_start(); // start the output buffer

    if ( $posts ) : ?>

        <div class="custom-posts-grid">
            <?php foreach ( $posts as $post ) : setup_postdata( $post ); ?>
                <?php if ( have_rows('poslovna_darila') ): ?>
                    <?php while ( have_rows('poslovna_darila') ) : the_row(); ?>
                        <div class="slider_slick">
                            <?php // vars
                            $image = get_sub_field('thumbnail_for_poslovna_darila');
                            $link = get_sub_field('url_poslovna_darila');
                            $count = count($posts);                         
                            ?>      
                            <div class="slide">
                                <a href="<?php echo $link; ?>">
                                <img src="<?php echo $image['url']; ?>" alt="<?php echo $image['alt'] ?>" class="image-overlay-post" />
                                </a>
                            </div>
                        </div>
                    <?php endwhile; ?>
                <?php endif; ?>                         
            <?php endforeach; ?>
            <?php wp_reset_postdata(); ?>
        </div>

    <?php endif;

    // return the contents of the output buffer as a string
    return ob_get_clean();     
}

add_shortcode( 'slick_slider' , 'get_slider' ); ?>