Print matched lines

grep.rkt

;;; grep.rkt --- Print matched lines

;; Author: Xu Chunyang <mail@xuchunyang.me>
;; Created: Tue, 03 Jul 2018 21:51:49 +0800
;; Updated: Wed, 04 Jul 2018 17:23:58 +0800
;; Homepage: https://gist.github.com/xuchunyang/3f9b4610c4cf6aff4647dc3ccafbdc26

;;; Commentary:

;; Example:
;; =======
;;
;; ~/gist $ emacs --version  | racket grep.rkt '[eE]macs'
;; GNU Emacs 25.3.1
;; GNU Emacs comes with ABSOLUTELY NO WARRANTY.
;; You may redistribute copies of GNU Emacs
;; ~/gist $ racket grep.rkt xuchunyang grep.rkt
;; ;; Author: Xu Chunyang <mail@xuchunyang.me>
;; ~/gist $

;;; Code:

#lang racket/base

(define (grep pattern input)
  (for ([line (in-lines input)])
    (when (regexp-match pattern line)
      (displayln line))))

(module+ main
  (require racket/cmdline)
  (command-line
   #:args (pattern [file (current-input-port)])
   (if (port? file)
       (grep pattern file)
       (call-with-input-file file
         (lambda (input)
           (grep pattern input))))))

;;; grep.rkt ends here