A very crude script to check if a domain name consists of 4 characters or less

four-chars-or-less.ml

let remove_substr str substr =
    Str.global_replace (Str.regexp substr) "" str;;

let remove_substrs str substrs =
    List.fold_left remove_substr str substrs;;

let get_domain_name str =
    let trimmed = remove_substrs str ["https://"; "http://"; "www"] in
    let domain_frags = String.split_on_char '.' trimmed in
    List.find (fun frag -> String.length frag > 0) domain_frags;;

let is_four_chars_or_less url =
    let name = get_domain_name url in
    (String.length name) <= 4;;

List.filter is_four_chars_or_less ["www.google.com"; "https://stfj.net"]

four-chars-or-less.rkt

#lang racket

(define (remove-substr substr str)
  (string-replace str substr ""))

(define (remove-substrs substrs str)
  (foldl remove-substr str substrs))

(define (get-domain-name url)
  (define trimmed (remove-substrs '("https://" "http://" "www") url))
  (define domain-frags (string-split trimmed "."))
  (car domain-frags))

(define (4-chars-or-less? url)
  (define name (get-domain-name url))
  (<= (string-length name) 4))

(filter 4-chars-or-less? '("www.google.com" "https://stfj.net"))

four-chars-or-less.scala

def removeSubstr(str: String, substr: String) =
  str.replaceAll(substr, "")

def removeSubstrs (str: String, substrs: List[String]) =
  substrs.foldLeft(str)(removeSubstr)

def getDomainName(domain: String) =
  val trimmed = removeSubstrs(domain, List("https://", "http://", "www"))
  val domainFrags = trimmed.split("\\.")
  domainFrags.find(_.length > 0).getOrElse("")

def isFourCharsOrLess(url: String) =
  val name = getDomainName(url)
  name.length <= 4

List("www.google.com", "https://stfj.net").filter(isFourCharsOrLess)