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

[Dr. Arne Babenhauserheide]

Roel Janssen <roel@gnu.org> writes:

> 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!

I’m not sure whether it’s better, but this is the solution I found:


(import (ice-9 rdelim) (ice-9 popen) (rnrs io ports))

(define (call-command-with-output-error-to-string cmd)
  (let* ((err-cons (pipe))
         (port (with-error-to-port (cdr err-cons)
                 (λ() (open-input-pipe cmd))))
         (_ (setvbuf (car err-cons) 'block 
             (* 1024 1024 16)))
         (result (read-delimited "" port)))
    (close-port (cdr err-cons))
    (values
     result
     (read-delimited "" (car err-cons)))))

(call-command-with-output-error-to-string "echo 1; echo 2 >&2")


Also available on my website:
https://www.draketo.de/software/guile-capture-stdout-stderr.html

Best wishes,
Arne
-- 
Unpolitisch sein
heißt politisch sein
ohne es zu merken

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