How to keep already-set GET parameter values on form submission?

Question

I have a URL : foo.php?name=adam&lName=scott, and in foo.php I have a form which gives me values of rectangleLength & re

Answer 1

My personal preference would be to specify the keys you wish to accept and be sure to run the value through htmlspecialchars().

$url_params = array(
  'tab'
);
foreach( $url_params as $key ) {
  echo !empty( $_GET[$key] ) ? '' : '';
}