PHP: Best practice for validating Option Select

I have a html form with an option select for choosing a country name see sample code bellow

I'm wondering how to validate this part of the form in PHP using filter input

filter_input(INPUT_POST, "Country", FILTER_VALIDATE_INT);

Will detect if no country has been selected because the value is 1
how would I validate a proper 3 figure country code

Is regex the best way or test for string length?  

<div >
 <select name="Country" >
  <option selected value=1>Please select</option>
  <option value="BRA">Brazil</option>
  <option value="NZL">New Zealand</option>
  <option value="SWZ">Switzerland</option>

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Steve BinkCommented:
When sanitizing user input, you should whitelist whenever possible.  In this case, you have a known number of acceptable answers.  Using a regex to detect good data is certainly acceptable.

To make things easier, you could have these options in a table.  For example:
CREATE TABLE `countries` (
	`abbr` CHAR(3) NOT NULL,
	`name` VARCHAR(50) NOT NULL,

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A simple SELECT gives you the array of possible values and names.  You can use that to build the select element, as well as filter the selection:
// assuming $countries = ['BRA'=>'Brazil','NZL'=>'New Zealand','SWZ'=>'Switzerland']
$is_valid = array_key_exists($user_selection, $countries);

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Julian HansenCommented:
$test = isset($_POST['Country']) 
   ? preg_match('/^[A-Z]{3}$/', $_POST['Country'], $country) 
   : false;

if (!$test) {
 // bad input
else {
  // If you get here you have an input comprising 3 capital letters - does not guarantee they are valid
  // country will now be in $country[0]

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What you can do (building on Steve's suggestion) is create a country table with a relationship setup to your data table on the country field.

If you try to insert a value into the data table (for country) - that does not exist in the country table the query will fail.
Vijaya KumarCommented:
Hope this helps  

  if (is_numeric($POST["Country"])) {
        echo "No country selected";
    } else {
      $country = array("brazil", "new land", "xxxx", "yyy");
      if (in_array($_POST["Country"], $country)) {
           echo "Got it";
         echo "no";
trevor1940Author Commented:
Thanx for your suggestions
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