(Unix 'cat' in Dis.  This is the language test; I shall be working on a)
('Hello, world' program presently.  In the meantime, here's cat with   )
(explanation:                                                          )

    * (Set the data pointer to 42--from the ASCII code of '*')
    ^ (Jump to label 1, below, via the ! at the new data pointer.)

||||||||||||||||||||||||||||||||
      (Placeholders.)

      (label 1:)
   }{ (Read a character, write, automatically die on EOF.)
    * (Set data pointer back to 42.)
    ^ (Read character, write character, repeat.)
||||| (More placeholders.)
 !||* (Data for jump and data pointer instructions which are used
       elsewhere.)