Re: How do you record output of both STDERR and STDIN to a string?

[Roel Janssen <roel@gnu.org>]

On Thu, 2020-09-10 at 04:14 +0300, Bonface M. K. wrote:
> Hi all. Is there a way to "record" the output from both *stderr* and
> *stdout* from a guile process if you wrap it around a "system" call
> to a
> string? Here's something that works. It's not /exactly/ what I want
> because "open-input-pipe" runs the command in a subprocess.
> 
> --8<---------------cut here---------------start------------->8---
> (define (run-job job)
>   (let* ((port (open-input-pipe job))
>          (str (read-line port)))
>     (close-pipe port)
>     str))
> 
> (display (format #t "~s ~s ~s"
>                  "padding"
>                  (run-job "echo hello")
>                  "testing"))
> --8<---------------cut here---------------end--------------->8---
> 
> I've tried out creating a fork:
> 
> --8<---------------cut here---------------start------------->8---
> (define (run-job thunk)
>   (call-with-output-string
>     (λ (port)
>       (match (pipe)
>         ((in . out)
>          (match (primitive-fork)
>            (0 ; child
>             (close in)
>             (with-error-to-port out thunk))
>            ((= waitpid (pid . exit-code)) ;; parent
>             (close out)
>             (display (read-line in) port))))))))
> 
> ;; Doesn't work:
> (display (format #t "~s ~s ~s"
>                  "padding"
>                  (run-job (system "echo hello"))
>                  "testing"))
> --8<---------------cut here---------------end--------------->8---
> 
> Ideally for a correct output without errors, I'd like to have as
> output:
> 
> --8<---------------cut here---------------start------------->8---
>  "padding" "hello" "testing"
> --8<---------------cut here---------------end--------------->8---
> 
> and in the event I have an error, like say, by running (system
> "echoooo hello"), I get
> the output:
> 
> --8<---------------cut here---------------start------------->8---
> "padding" "sh: command not found" "testing""
> --8<---------------cut here---------------end--------------->8---
> 
> PS: I'm new to Guile :)
> 

Having spent a day on this myself, this is the best I had come up with:

--8<---------------cut here---------------start------------->8---
(define (virtuoso-isql-query query)
  "Executes QUERY via ISQL and returns a both an ERROR-PORT and a PORT
to read CSV output from."
  (let* ((tmp        (getenv "TMPDIR"))
         (error-port (mkstemp! (string-append (if tmp tmp "/tmp") "/sg-
XXXXXX")))
         (port       (open-input-pipe
                      (format #f "~a ~a -U ~a -P ~a verbose=off
csv_rfc4180=on csv_rfc4180_field_separator=, exec='~:a' 2> ~a"
                              (isql-bin) (isql-port) (rdf-store-
username)
                              (rdf-store-password)
                              (string-append "SPARQL " query)
                              (port-filename error-port)))))
    (setvbuf port 'block 4096)
    (values error-port port)))
--8<---------------cut here---------------end--------------->8---

I certainly hope someone can come up with a better solution!

Kind regards,
Roel Janssen