Irule for Redirecting 15 paths to new url

You have an errant closing square bracket after your conditional if statement and the "genreperspective" string would be in the [HTTP::host] value, not the [HTTP::path]. Otherwise, if you can guarantee that the "/2013/x/x" URI pattern always exists before the URI portion that you want to capture, then you can also do this:

when HTTP_REQUEST {
    if { [string tolower [HTTP::host]] equals "www.genreperspective.com" } {
        set newuri [lindex [split [HTTP::uri] "/"] 4]
        HTTP::redirect "http://www.genre.com/knowledge/blog/${newuri}.html" 
    }
}

This is simply splitting the incoming URI into a list and plucking out the 5th element (similar to Pete's getfield command).