guile-examples/shell/example-03-using-popen-get-out-and-error.scm

;;; ABOUT

;; The examples in this document were posted on the Guile
;; user mailing list and are not originally written by me
;; zelphirkaltstahl@posteo.de.

;; Comments, some formatting and editing by me
;; (zelphirkaltstahl@posteo.de).

;; The following code is adapted from a post on the Guile
;; user mailing list, posted by post@thomasdanckaert.be and
;; is part of
;; https://github.com/tdanckaert/jobview/blob/master/jobtools.scm#L38.


(import (ice-9 popen)
        (ice-9 textual-ports)
        (ice-9 exceptions)
        (ice-9 receive)
        (ice-9 match))


;; Removed comments to shorting this example. For more
;; explanation see the first example.
(define run-command
  (λ (cmd)
    "Runs CMD as an external process, with an input port
from which the process' stdout may be read."
    (match-let ([(err-read . err-write) (pipe)]
                [stderr (current-error-port)])
      (with-error-to-port err-write
        (λ ()
          (let* (;; Run the actual command. If an error
                 ;; happens, it should write to the
                 ;; err-write port. Output of the command
                 ;; should be written to an output port,
                 ;; which corresponds to the input-port,
                 ;; which is returned by open-input-pipe.
                 [in-port (open-input-pipe cmd)]
                 ;; Read in block mode.
                 [_ignored (setvbuf in-port 'block)]
                 ;; Get command output and error output.
                 [command-output (get-string-all in-port)]
                 ;; Get the exit code of the command.
                 [exit-code (close-pipe in-port)])
            ;; Close the port, to which the child process
            ;; was to write errors, as the child process has
            ;; finished (either successfully or
            ;; unsuccessfully, but definitely finished).
            (close-port err-write)
            (let (;; Get the error message, if there is any.
                  [error-message (get-string-all err-read)])
              (values exit-code
                      command-output
                      error-message))))))))


(receive (exit-code command-output error-message)
    (let ([command "echo 'bong' 1>&2"])
      (run-command command))
  (display (simple-format #f "exit code: ~a\n" exit-code))
  (unless (string-null? command-output)
    (display (simple-format #f "command-output: \n~a" command-output)))
  (unless (string-null? error-message)
    (display (simple-format #f "error-message: \n~a" error-message))))


(receive (exit-code command-output error-message)
    (let ([command "ls -al"])
      (run-command command))
  (display (simple-format #f "exit code: ~a\n" exit-code))
  (unless (string-null? command-output)
    (display (simple-format #f "command-output: \n~a" command-output)))
  (unless (string-null? error-message)
    (display (simple-format #f "error-message: \n~a" error-message))))


;; Both, output and error:
(receive (exit-code command-output error-message)
    (let ([command "ls -al 2>&1 && echo 'bong' 1>&2"])
      (run-command command))
  (display (simple-format #f "exit code: ~a\n" exit-code))
  (unless (string-null? command-output)
    (display (simple-format #f "command-output: \n~a" command-output)))
  (unless (string-null? error-message)
    (display (simple-format #f "error-message: \n~a" error-message))))


;; With failing command:
(receive (exit-code command-output error-message)
    (let ([command "lsasdasd -al"])
      (run-command command))
  (display (simple-format #f "exit code: ~a\n" exit-code))
  (unless (string-null? command-output)
    (display (simple-format #f "command-output: \n~a" command-output)))
  (unless (string-null? error-message)
    (display (simple-format #f "error-message: \n~a" error-message))))