grep.scm

(import (ice-9 regex)
        (ice-9 rdelim))

(define (grep ps . fns)
  (define re (make-regexp ps))
  (define (grep-int p r)
    (let ((l (read-line p)))
      (if (not (eof-object? l))
          (begin
            (if (regexp-match? (regexp-exec r l))
                (begin
                  (display l)
                  (newline)))
            (grep-int p r)))))

  (if (null? fns)
      (grep-int (current-input-port) re)
      (for-each
       (lambda (fn)
         (call-with-input-file fn
           (lambda (p) (grep-int p re))))
       fns)))

(define (main args)
  (apply grep (cdr args)))