iRule recognize blank space in URI?

"[TCP::payload] matches_regex "/vMoD.+Y" is a boolean comparison. It's outcome of 0 or 1 is not a command and can't be enclosed in brackets (which indicate execution of a command). If you want to extract the content, then you will have to use one of the builtin regular expression commands like regexp (Click here).

You could do something like this to look for your pattern

when CLIENT_DATA {
   regexp returns 1 if a match is found
  if { [regexp "/vMoD.+Y" [TCP::payload] match] }
    log local0. "match found: $match"
  } else {
    log local0. "no match"
  }
}

Keep in mind that this will not return the entire URI but only the matched content. So for an URI of "http://www.foo.com/vMoDblahblahY?foobar" the value of match would be "/vMoDblahblahY" since that is the exact content that matches the pattern you requested.

To look for the full URI you are going to have to expand you regular expression to cover the rest of it.

-Joe