\ clear explicit version
  s =: "Hello,How,Are,You,Today"
  r =: string s split by any of ','     \ single character split
  print join r by '.'
  \ all in one, no parenthesis required
  print join string "Hello,How,Are,You,Today" split by any of ',' by '.'
  \ parenthesis for clarity
  print (join (string "Hello,How,Are,You,Today" split by any of ',') by '.')