WordPress Standard Add Shortcode Function

function do_imnobby_standard_wp_shortcode($attr){
 
 $tmphtml = '';

 $tmphtml .= $attr["showtext"];
 
 return $tmphtml;
 
}
add_shortcode( 'imnobby_standard_wp_shortcode', 'do_imnobby_standard_wp_shortcode' );

// [ imnobby_standard_wp_shortcode showtext="show_this_text" ]