Re: Shell commands with output to string

[Olivier Dion via General Guile related discussions <guile-user@gnu.org>]

On Tue, 22 Feb 2022, Leo Butler <leo.butler@umanitoba.ca> wrote:
> Olivier Dion via General Guile related discussions <guile-user@gnu.org>
> writes:
>
>> On Tue, 22 Feb 2022, Zelphir Kaltstahl <zelphirkaltstahl@posteo.de> wrote:
>>> Hello Guile users!
>>>
>>> How would I run a shell command from inside Guile and get its output
>>> as a string, instead of the output being outputted directly? (Guile
>>> 3.0.8)
>>
>> I use the following:
>>
>> (define-module (shell utils)
>>   #:use-module (ice-9 format)
>>   #:use-module (ice-9 popen)
>>   #:use-module (ice-9 textual-ports))
>>
>> (define (shell% proc fmt . args)
>>   (let* ((port (open-input-pipe (format #f "~?" fmt args)))
>>          (output (proc port)))
>>     (close-pipe port)
>>     output))
>
> You probably want to inspect the exit value of the shell process, so
> that you can handle/throw the error. This is what I use (similar to your
> `shell'):

You're absolutely right.  It would also probably a good idea to use
dynamic-wind for close-pipe in case an exception is thrown in
read-string I think.

>
> (define* (shell-command-to-string cmd)
>   (catch 'shell-command-error
>     ;; thunk                                                                                                                                                                                                                        
>     (lambda ()
>       (let* ((port (open-pipe cmd OPEN_READ))
>              (str (read-string port))
>              (wtpd (close-pipe port))
>              (xval (status:exit-val wtpd)))
>         (if (or (eqv? xval #f) (> xval 0)) (throw 'shell-command-error cmd str))
>         str))
>     ;; handler                                                                                                                                                                                                                      
>     (lambda (key cmd str)
>       (simple-format #t "ERROR: in command ~a\nstring: ~a\n" cmd str)
>       (throw 'error-in-shell-command-to-string cmd str))))
>
>>
>> (define-public (shell . args)
>>   (apply shell% (cons get-string-all args)))
>>
>> (define-public (shell$ . args)
>>   (apply shell% (cons get-line args)))
>>
>> Then
>> (shell "ls" "-l")
>>
>> The $ variant is to get a single line in the output.
>
> I wonder why there is no module already in ice-9 which does this
> stuff?  It seems like a lot of people are re-inventing the wheel.

There's ton of missing stuffs in the standard library IMO.  On top of my
head, filesystem paths manipulation (e.g. path-join) is also one that is
probably getting re-invented a lots.

I believe that the successful story of Python is not just about its
pretty syntax, but also dues to its very large standard library.

-- 
Olivier Dion
Polymtl