[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Q] HOWTO redirect a i/o-port in Unix??
Quoting Leo Razoumov:
> More specifically, I am looking for a way to redirect stdout (and stderr) of a
> subprocess created with (process "myprog") into a file.
Quoting Matthias Felleisen:
> Here is a (stupid) trick that I used in my Web page building scripts:
> (with-output-to-file "date.txt"
> (lambda ()
> (display (read-line (car (process "date"))))))
> This copies text from the process port to the file "date.txt".
That works often. But sometimes the data coming from the process isn't
line-based, and often you want the data to get pushed from one port to
the other "in the background".
Here's a fairly general and efficient function:
(define (copy-stream input-port output-port)
(thread (lambda ()
(let ([s (make-string 4096)])
(let loop ()
(let ([l (read-string! s input-port)])
(unless (eof-object? l)
(display (if (< l 4096) (substring s 0 l) s)
;; For most contexts, it's good to
;; close the ports at this point:
Here's an example of its use:
;; Pipe "ls" output to "wc":
(define ls-p (process "ls"))
(define wc-p (process "wc"))
(copy-stream (car ls-p) ; car is stdout of ls
(cadr wc-p)) ; cadr is stdin of wc-p
(define t (copy-stream (car wc-p)
;; wait until "wc" is done: