How to execute program from Clojure without any external libraries and showing its output at real time?

Question

My attempt:

(import 'java.lang.Runtime)
(. (Runtime/getRuntime) exec (into-array ["youtube-dl" "--no-playlist" "some youtube video link"]))

I also tried sh. But both approaches don't do what I want - running a program similarly like shell does (sh waits until program exits, exec launches it and doesn't wait for its exit; both don't output anything to standard output). I want live showing of process output, e.g. when I run youtube-dl I want to see progress of a video download.

How to do this simple simple task in Clojure?

Minh Tuan Nguyen · Accepted Answer · 2017-08-26 13:21:03Z

2

You must start the process and listen to its output stream. One solution is :

(:require [clojure.java.shell :as sh]
          [clojure.java.io :as io])

(let [cmd ["yes" "1"]
      proc (.exec (Runtime/getRuntime) (into-array cmd))]
      (with-open [rdr (io/reader (.getInputStream proc))]
        (doseq [line (line-seq rdr)]
          (println line))))

answered Aug 26, 2017 at 13:21

Minh Tuan Nguyen

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2 Comments

monnef Over a year ago

It's not exactly same as shell does it (e.g. shell allows to "rewrite" current line, so for example progress bar is always shown only once), but it's close enough. Thank you :).

Minh Tuan Nguyen Over a year ago

In my example I just use the println function. For the rewrite behaviour you must implement your own println function that prints the carriage return. See: stackoverflow.com/questions/9566654/…

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