使用mechanize时使用正则表达式查找具有特定锚点的链接

I'm trying to use the Mechanize link_with(:href => 'anchor here') in order to find pages that have links with a certain string in the href. For example I want it so that I can spit out into a text file all sites that have a link where the anchor contains "index.php?user"I'm trying to use the Mechanize link_with(:href