<?php
$string = "
CLIENT_LIST	orion-01889596000195	177.43.212.110:28763	172.16.191.145	872199	860412	Wed May 25 07:22:52 2016	1464171772	UNDEF
CLIENT_LIST	elgin-05997632000195	189.10.58.244:62588	172.16.6.210	301365	250459	Wed May 25 07:01:37 2016	1464170497	UNDEF
CLIENT_LIST	databits-13031005000123	187.17.235.203:50515	172.16.136.217	459833	409771	Wed May 25 06:09:01 2016	1464167341	UNDEF
CLIENT_LIST	UNDEF	201.14.8.164:1134		42	54	Wed May 25 15:05:07 2016	1464199507	UNDEF
CLIENT_LIST	elgin-15259334000151	187.5.4.138:56256	172.16.19.10	172756	170025	Wed May 25 08:26:39 2016	1464175599	UNDEF

";

function processador($str){
    $partes = preg_split("/\t/", trim($str));
    $data = array_slice($partes, 1); 
    return array_map("filtro", $data);
}
function filtro($str){
    return str_replace("UNDEF", "", $str);
}

$linhas = array_filter(explode("\n", $string));
$resultado = array_map("processador", $linhas);

echo var_dump($resultado);