Felix Lechner via "Bug reports for GUILE, GNU's Ubiquitous Extension Language"
<bug-guile@gnu.org> writes:
> Hi,
>
> In an interesting (or perhaps maddening) inconsistency,
> 'with-output-to-port' captures stdout from system* here
>
> (call-with-output-file "/tmp/test.log"
> (lambda (port)
> (with-output-to-port
> port
> (lambda ()
> (system* "mktemp" "-d")))))
>
> but 'with-output-to-string' does not do so here
>
> (with-output-to-string
> (lambda ()
> (system* "mktemp" "-d")))
>
> According to lloda on #guile, system* handles the redirection only
> when the current ports are file ports. Thanks for that pointer!
That’s correct. I’ve been using the following monstrosity to capture
and process output. Perhaps someone finds a prettier way?
--8<---------------cut here---------------start------------->8---
(define* (call-with-output-processor command proc #:optional capture-stderr?)
"Silently execute COMMAND, a list of strings representing an
executable with its arguments, and apply PROC to every line printed to
standard output and, optionally when CAPTURE-STDERR? is #T, standard
error. Return the exit status of COMMAND."
;; We can only capture a program's standard error by parameterizing
;; current-error-port to a *file* port before using system* or
;; open-pipe*. The process will write its standard error stream to
;; the provided file descriptor. Meanwhile we read from the file
;; descriptor (blocking) for new lines until the process exits.
(match (socketpair PF_UNIX SOCK_STREAM 0)
((in . out)
(let ((err (if capture-stderr?
(dup out)
(%make-void-port "w"))))
(catch #true
(lambda ()
(let ((thread
(parameterize ((current-error-port err)
(current-output-port out))
(call-with-new-thread
(lambda ()
(let ((status
(status:exit-val
(apply system* command))))
(close-port err)
(close-port out)
status))))))
(let loop ()
(match (read-line in 'concat)
((? eof-object?)
(for-each
(lambda (port)
(false-if-exception (close-port port)))
(list err out in))
(join-thread thread))
(line
(proc line)
(loop))))))
(lambda (key . args)
(for-each
(lambda (port)
(false-if-exception (close-port port)))
(list err out in))
(apply throw key args)))))))
--8<---------------cut here---------------end--------------->8---
--
Ricardo
