I've created a meta box. The code is:

/**
 * Add meta box 
 *
 * @param post $post The post object
 * @link 
 */
function portfolio_add_meta_boxes( $post ){
    add_meta_box( 'portfolio_meta_box', __( 'Company URLs', 'portfolio' ), 'portfolio_build_meta_box', 'portfolio', 'side', 'low' );
}
add_action( 'add_meta_boxes_portfolio', 'portfolio_add_meta_boxes' );

/**
 * Build custom field meta box
 *
 * @param post $post The post object
 */
function portfolio_build_meta_box( $post ){
    // make sure the form request comes from WordPress
    wp_nonce_field( basename( __FILE__ ), 'portfolio_meta_box_nonce' );

    // retrieve the  current value
    $fbportfolio = get_post_meta( $post->ID, 'fbportfolio', true );
    $twportfolio = get_post_meta( $post->ID, 'twportfolio', true );
    $instportfolio = get_post_meta( $post->ID, 'instaportfolio', true );
    $linkinportfolio = get_post_meta( $post->ID, 'linkinportfolio', true );

    ?>
    <div class='inside'>

        <h3>Facebook</h3>
        <p>
        <input type="url" name="fbportfolio" value="<?php echo $fbportfolio; ?>">
        </p>

    
    
    </div>
    <?php
}

/**
 * Store custom field meta box data
 *
 * @param int $post_id The post ID.
 * @link 
 */
function portfolio_save_meta_box_data( $post_id ){

    // store custom fields values
    update_post_meta( get_the_ID(), 'fbportfolio', $_POST['fbportfolio'] );


}
add_action( 'save_post_food', 'portfolio_save_meta_box_data' );

I've created a meta box. The code is:

/**
 * Add meta box 
 *
 * @param post $post The post object
 * @link https://codex.wordpress/Plugin_API/Action_Reference/add_meta_boxes
 */
function portfolio_add_meta_boxes( $post ){
    add_meta_box( 'portfolio_meta_box', __( 'Company URLs', 'portfolio' ), 'portfolio_build_meta_box', 'portfolio', 'side', 'low' );
}
add_action( 'add_meta_boxes_portfolio', 'portfolio_add_meta_boxes' );

/**
 * Build custom field meta box
 *
 * @param post $post The post object
 */
function portfolio_build_meta_box( $post ){
    // make sure the form request comes from WordPress
    wp_nonce_field( basename( __FILE__ ), 'portfolio_meta_box_nonce' );

    // retrieve the  current value
    $fbportfolio = get_post_meta( $post->ID, 'fbportfolio', true );
    $twportfolio = get_post_meta( $post->ID, 'twportfolio', true );
    $instportfolio = get_post_meta( $post->ID, 'instaportfolio', true );
    $linkinportfolio = get_post_meta( $post->ID, 'linkinportfolio', true );

    ?>
    <div class='inside'>

        <h3>Facebook</h3>
        <p>
        <input type="url" name="fbportfolio" value="<?php echo $fbportfolio; ?>">
        </p>

    
    
    </div>
    <?php
}

/**
 * Store custom field meta box data
 *
 * @param int $post_id The post ID.
 * @link https://codex.wordpress/Plugin_API/Action_Reference/save_post
 */
function portfolio_save_meta_box_data( $post_id ){

    // store custom fields values
    update_post_meta( get_the_ID(), 'fbportfolio', $_POST['fbportfolio'] );


}
add_action( 'save_post_food', 'portfolio_save_meta_box_data' );

• custom-post-types
• post-meta

2 Answers 2

add_action( 'save_post', ...

and test if your post type is tour custom post type.

You can avoid needing to test for the post type in the save_post action by using save_post_{post_type}

E.g.

add_action( 'save_post_portfolio', .....

Where portfolio is the post type being saved. Using save_post will run your code for all posts types unless explicitly checked.