This should do it.

Code:
on *:TEXT:search *:?:{
  var %string = $2-
  var %file = filename.txt

  var %cnt = 1
  var %ttl = $lines(%file)
  while (%cnt <= %ttl) {
    var %temptext = $read(%file,%cnt)
    if (%string isin %temptext) { msg $nick %temptext }
    inc %cnt
  }
}


Just specify the filename in the line: var %file = xxx.txt