<?
    switch($_GET['kw']){

        case "berlingo":
            include 'berlingo.php'
            break;
        case "c4":
            include 'c4.php';
            break;

    }
?>

$linkKW = $_GET['kw'];

switch (true){
   case stristr($linkKW,'berlingo'):
      include 'berlingo.php';
      break;
   case stristr($linkKW,'c4'):
      include 'c4.php';
      break;
}

$linkKW = $_GET['kw'];

switch (true){
   case stripos($linkKW,'berlingo') !== false:
      include 'berlingo.php';
      break;
   case stripos($linkKW,'c4') !== false:
      include 'c4.php';
      break;
}

if (strpos($_GET['kw'], 'berlingo') !== false) {
    include 'berlingo.php';
} else if (strpos($_GET['kw'], 'c4') !== false) {
    include 'c4.php';
} … and so on …

$map = array('berlingo' => 'berlingo.php', 'c4' => 'c4.php', …);
foreach ($map as $keyword => $file) {
    if (strpos($_GET['kw'], $keyword) !== false) {
        include $file;
        break;
    }
}

$keywords = array('berlingo', 'c4', …);
foreach ($keywords as $keyword) {
    if (strpos($_GET['kw'], $keyword) !== false) {
        include "$keyword.php";
        break;
    }
}

if(strpos($_GET['kw'],'berlingo') !== false) {
 include 'berlingo.php';
}
if(strpos($_GET['kw'],'c4') !== false) {
 include 'c4.php';
}

$keywords = array('berlingo', 'c4');
foreach($keywords as $keyword)
  if(strpos($_GET['kw'], $keyword) !== FALSE)
    include("$keyword.php");

<?php

    $kw = filter_input(INPUT_GET, "kw");

    switch($kw){

        case (preg_match('/*berlingo*/', $kw) ? true : false):
            include 'berlingo.php';
            break;

        case "c4":
            include 'c4.php';
            break;

    }
?>

$map = array('berlingo' => 'berlingo.php', 'c4' => 'c4.php', …);

if( !isset( $map[$_GET['kw']] ))
    throw new Exception("Blah!!");

include $map[$_GET['kw']];

class Haystack {
    public $value;

    public function __construct($value)
    {
        $this->value = $value;
    }

    public function contains($needle):
    {
        if (strpos($this->value, $needle) !== false)
            return $this;
    }
}

$kw = new Haystack($_GET['kw']);

switch ($kw) {
    case $kw->contains('berlingo'):
        require_once 'berlingo.php';
    case $kw->contains('c4'):
        require_once 'c4.php';
}

final class Haystack {
    private $value;
    private $isMain;

    public function __construct(string $value, bool $isMain = true)
    {
        $this->value = $value;
        $this->isMain = $isMain;
    }

    final public function contains($needle): Haystack
    {
        if (strpos($this->value, $needle) !== false)
            return $this;
        return new Haystack($needle, false);
    }
}