こうなりました。with-ports を使おうとしたら、
*** ERROR: unbound variable: with-ports
となりました。何故？

#!/usr/bin/gosh
(use gauche.charconv)

(define raw-in (current-input-port))
(define raw-out (current-output-port))
(define in (wrap-with-input-conversion raw-in "eucjp"))
(define out (wrap-with-output-conversion raw-out "eucjp"))

(define line #f)

(define (main args)
  (while (not (eof-object? (set! line (read-line in))))
  (display (string-append line "\n") out))
  0)