How can I create a shortcode in my custom plugin PHP file

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PHP

WordPress

Hi, I am creating a custom plugin and want to create a shortcode in this file.
I am using this code

function wpb_resultData_shortcode() {
     $message="hello";
     echo $message;

}

add_shortcode('show_Data', 'wpb_resultData_shortcode');

And using the [show_Data] in my page I am not getting the data

What I have tried:

function wpb_resultData_shortcode() {
     $message="hello";
     echo $message;

}

add_shortcode('show_Data', 'wpb_resultData_shortcode');