auto-affiliate-links.php

<?php
function replace_text_wps($text){  
    $replace = array(  
    // Choose the words to replace & what to replace it with  
    'plugindrawer' => '<a href="http://plugindrawer.com/myafflink">plugindrawer</a>',  
    'backupbuddy' => '<a href="http://ithemes.com/myafflink">backupbuddy</a>'  
    );  
    $text = str_replace(array_keys($replace), $replace, $text);  
    return $text;  
}  
  
add_filter('the_content', 'replace_text_wps');  
add_filter('the_excerpt', 'replace_text_wps'); 
?>