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Re: Bug in system?

From: Alexei Matveev
Subject: Re: Bug in system?
Date: Wed, 7 Nov 2012 19:15:50 +0100

On 7 November 2012 03:49, Keith Wright <address@hidden> wrote:

 > (define y (with-output-to-string (lambda()(system "date"))))
  Tue Nov  6 21:42:41 EST 2012
 > y
  $2 = ""

The stdout of the system call does not go into the string,
why not?

For the same reason you cannot capture stdout of, say,
printf() in the native code to a file using


I am not qualified to judge if these are valid reasons, though.
I used the code below to achieve that.


;;; Beware that writing to the  same file from multiple workers is not
;;; going to end good:
(define (with-stdout-to-file file proc)
  (with-output-to-file file
    (lambda ()
      (let ((dup-1 (dup 1))         ; make a dup of the current stdout
            (fd (fileno (current-output-port))))
        (dup2 fd 1)     ; close stdout and redirect it to fd
        (proc)          ; execute thunk with stdout redirected to file
        (dup2 dup-1 1)  ; close file, stdout to original destination
        (close dup-1)))))               ; dont leak file descriptors

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