ACF Field Shortcode

1. **Create a custom shortcode in your theme's `functions.php` file**:

function display_acf_field_by_post_id($atts) {
    // Set default attributes
    $atts = shortcode_atts(
        array(
            'field' => '', // ACF field name (required)
        ),
        $atts,
        'acf_field' // Shortcode name
    );

    // Get the current post ID
    $post_id = get_the_ID();

    // If no post ID is found, return an empty string
    if (!$post_id) {
        return '';
    }

    // Get the ACF field value
    $field_value = get_field($atts['field'], $post_id);

    // If the field exists and has a value, return it
    if ($field_value) {
        return $field_value;
    }

    // If no field value found, return a default message
    return 'No content available for this field.';
}

add_shortcode('acf_field', 'display_acf_field_by_post_id');

### Explanation:
– **`$atts`**: This is the array of attributes passed to the shortcode. Here we set a default attribute `field`, which specifies the ACF field name you want to display.
– **`get_the_ID()`**: This function retrieves the current post ID.
– **`get_field()`**: This function gets the value of the ACF field for the given post ID.
– **Shortcode**: `[acf_field field="your_acf_field_name"]` will display the ACF field value for the current post.

### Usage:
In the post or page editor, you can now use the shortcode like this:

[acf_field field="your_acf_field_name"]

Replace `"your_acf_field_name"` with the actual name of the ACF field you want to display.

This will display the ACF field content based on the current post ID. If no content is available, it will show `"No content available for this field."`

### Steps:

1. **Create the custom shortcode in your theme's `functions.php` file**:

function display_acf_field_by_post_id() {
    // Get the current post ID
    $post_id = get_the_ID();

    // If no post ID is found, return an empty string
    if (!$post_id) {
        return '';
    }

    // Set the ACF field key you want to retrieve (replace with your actual ACF field name/key)
    $acf_field_key = 'your_acf_field_name';  // Replace 'your_acf_field_name' with the field key or name

    // Get the ACF field value
    $field_value = get_field($acf_field_key, $post_id);

    // If the field exists and has a value, return it
    if ($field_value) {
        return $field_value;
    }

    // If no field value is found, return a default message
    return 'No content available for this field.';
}

add_shortcode('acf_field', 'display_acf_field_by_post_id');

### Explanation:
– **No attribute passed**: The shortcode does not accept any attributes from the user. Instead, it directly references the ACF field key or name (`your_acf_field_name`).
– **`get_the_ID()`**: It retrieves the current post's ID.
– **`get_field()`**: It retrieves the value of the ACF field associated with the current post ID.
– **Field key**: The ACF field is identified by its name or key (`your_acf_field_name`). You should replace `'your_acf_field_name'` with the actual field name (the same name you defined in ACF).

### Usage:
In your post or page editor, you can use the shortcode like this:

[acf_field]

This shortcode will display the content of the ACF field associated with the current post. If the field is empty or does not exist, it will display `"No content available for this field."`

### Notes:
– **Replace `'your_acf_field_name'`** with the actual ACF field key or name that you want to display.
– This method is useful when you want to show a specific field for every post/page without passing any parameters.