John

<?php

$re = "/(?<=affiliatewire_)[^_\r\n]++/"; 
$str = "param0_test1_param1_affiliatewire_name1_test2_param2_param3
param0_test1_param1_affiliatewire_name_test2_param2_param3
param0_test1_param1_affiliatewire_trollolo_test2_param2_param3"; 

preg_match_all($re, $str, $matches);

print_r($matches);
?>

Array
(
    [0] => Array
        (
            [0] => name1
            [1] => name
            [2] => trollolo
        )

)

$main_str = 'abracadabra-cudsa_123-qwerty-text_a-abraca-trollololo-nlo';

//искомый текст
$my_str = '/text_a|text_b/';

$matches = array();
preg_match_all($my_str, $main_str, $matches);

if (array_search('text_a', $matches[0]) !== false)
  echo 'Привет, Васа!';
elseif(array_search('text_b', $matches[0]) !== false)
  echo 'Привет, Лана!';
else
  echo 'Привет, Мир!';