In need of some iRule HELP!! URI Path stuff.

You can build a class of your CSID's then reference your class for pool pl_1 inclusion:

class myCSID {
 "b02181"
 "h05527"
}
when HTTP_REQUEST {
  set CSID [string tolower [URI::path [HTTP::uri] 1 1]]
  if { [matchclass $CSID equals $::myCSID] } {
    pool pl_1
  } else {
      pool pl_2
  }
}

If you ever had more pools, you could alter the class to include the pool reference, then use findclass to extract it:

class myCSID {
  "b02181 pl_1"
  "h05527 pl_1"
  "x07770 pl_2"
  "y07070 pl_3"
}
when HTTP_REQUEST {
  set CSID [string tolower [URI::path [HTTP::uri] 1 1]]
  if { [matchclass $CSID equals $::myCSID] } {
    pool [findclass $CSID $::myCSID " "]
  } else {
      pool defaultPool
  }
}

HTH, std disclaimer....untested!