Compare user-agent content and then match?

Hi,

I'm looking solution to match botnets width fake user-agent and width fake user-agent syntax.

First check, is the user-agent complete:

Mozilla/5.0 (Linux; Android 4.4.2; SM-G7102 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.84 Mobile Safari/537.36 - good
Mozilla/5.0 (Linux; Android 4.4.2) - bad

Second check, if the user-agent version is having too much or too less digits:

Mozilla/1.2.3 (Linux; U; Android 1.2.3) - more then 3, bad, match
Mozilla/1.2 (Linux; U; Android 1.2) - less then 2, bad, match

Third check to match all which are using same number twice and are equal in user-agent, for example:

Mozilla/1.2.3 (Linux; U; Android 1.2.3) - bad, match

I managed somehow to match fist 2 conditions, but how to match third condition? How to compare strings inside user-agent and if they are equal, then match as bad and drop?

when HTTP_REQUEST {
    set uagent [string tolower [HTTP::header User-Agent]]
    set uri [string tolower [HTTP::uri]]
    set headers ""
    foreach aHeader [HTTP::header names] { set headers "$headers $aHeader: [HTTP::header value $aHeader];" }
    switch -glob $uagent {
        "mozilla/[0-9].[0-9].[0-9] (linux; u; android [0-9].[0-9].[0-9])"
        {
            if { ( ($uri starts_with "/admin.php") && ([HTTP::header Referrer] equals "") and ([string length $osversion] < 3) or ([string length $osversion] > 5) } then {
                event disable all
                TCP::close
                log local0. "BAD"
                return
            }
        }
        default {
            log local0. "GOOD"
        }
    }
}