4.2.2 Annotated examples

4.2.2.1 Running a program

;;; This function prints the output from a program that has been 
;;; started with RUN-PROGRAM. On a heavily loaded system, pauses
;;; in program output can cause premature termination of this
;;; function. In this case the  function can simply be called
;;; again to get the rest of the output.
> (defun type-until-hung (stream) 
    (do ((char (read-char-no-hang stream)   
               (read-char-no-hang stream))) 
        ((null char)) 
     (write-char char))) 
TYPE-UNTIL-HUNG

;; The shell is set to the stream that is used for standard input
;; and standard output for csh.  The terminal remains the standard
;; error output stream.
> (setq shell (run-program "csh" :input :stream :output :stream
                              :wait nil))
#<Stream BUFFERED-STREAM 101BF73B>          

;; Send a banner command to csh.
> (format shell "/usr/games/banner test~%") 
NIL

> (force-output shell)
NIL

;; Print the output from banner.
> (type-until-hung shell) 
  #####  ######   ####    #####
    #    #       #        #
    #    #####    ####     #
    #    #            #   #
    #    #       #    #   #
    #    ######   ####     #
NIL

;; Send an erroneous command to the shell.
> (format shell "unknown~%") 
NIL

> (force-output shell)
NIL

> unknown: Command not found.           ; This is standard output; 
                                     ; it is not trapped.
(type-until-hung shell)                 ; No output was sent to the
NIL                                   ; standard output.

;; Make csh exit.
> (format shell "exit~%")
NIL

;; Close the stream used for standard input and output.
> (close shell)                             
NIL

Note: Many UNIX programs exit on reading an end-of-file indicator from the standard input stream. If you run a program that does not, you should always give it an exit command before you close its input stream.

Generated with Harlequin WebMaker