How to get index position of an item from array in php

array_search() — Searches the array for a given value and returns the corresponding key if successful.

<?php
   $array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red'); 
   $key = array_search('green', $array); // $key = 2;
   $key = array_search('red', $array);   // $key = 1;
?>