output common int using array_search

I am trying to create a function that will output the smallest common int or return false if there is not one in three arrays. The arrays are sorted ascending and I want to do with array_search.

When I execute this code it returns nothing and I don’t know why it should echo 5 I think

<?php
$a=array(1,2,3,5,6);
$b=array(2,3,4,5,6);
$c=array(4,5,6,7,8);
$arrlength = count($a);

function smallest_common_number(){
    global $a, $b, $c;
    foreach ($a as $value) {
      $x=array_search($a[0], $b);
         array_search($x,$c);
         echo $x
    }
}

smallest_common_number();
?>

Answer

Here is a different method of doing it.

First I find the lowest number that it could possibly be $min.

Then I loop the $a array and skip until I find at least $min.
if array search of $b and $c is not false then we found the lowest possible match and break the code.

function smallest_common_number(){
    global $a, $b, $c;
    $min = max(min($a), min($b), min($c));

    foreach ($a as $value) {
        if($value >= $min){
            if(array_search($value, $b) !== false && array_search($value, $c) !== false){
                echo $value;
                break;
            }
        }
    }
}

But the simplest code is probably array_intersect. But OP asked for array_search…

function smallest_common_number(){
    global $a, $b, $c;
    echo min(array_intersect($a, $b, $c));
}