Mimic GNU yes' behavior of cmdline arguments.

yes.scm

(use-modules (ice-9 binary-ports)
             (rnrs bytevectors))

(define (build-string s n)
  (let* ((s2 (string-append s "\n"))
         (s2len (string-length s2)))
    (let A ((s3 (string-copy s2))
            (s3len s2len))
      (if (> (+ s3len s2len) n)
          s3
          (A (string-append s3 s2) (+ s3len s2len))))))

(define (yes args)
  (let ((args-str
         (let ((t (cdr args)))
           (if (null? t) "y" (string-join t " ")))))
    (let ((stdout (current-output-port))
          (yyy (string->utf8 (build-string args-str 8192))))
      (setvbuf stdout 'block 8192)
      (let A ()
        (put-bytevector stdout yyy)
        (A)))))