is a letter php code example
Example 1: php string only letters
$result = preg_replace("/[^a-zA-Z0-9]+/", "", $s);
Example 2: if is alphabet php
ctype_alpha ( string $text ) : bool
$result = preg_replace("/[^a-zA-Z0-9]+/", "", $s);
ctype_alpha ( string $text ) : bool