Re: Shell commands with output to string

[Zelphir Kaltstahl <zelphirkaltstahl@posteo.de>]

Hi Oliver!

On 2/22/22 17:33, Olivier Dion wrote:
> 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 actually made something for that, trying to copy mostly the Python behavior 
for os.path.join:

https://notabug.org/ZelphirKaltstahl/guile-fslib

Also available as a GNU Guix package, but not updated in a while on Guix. 
Repository contains more up to date version.

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

I think so too. Although I sometimes have the feeling, that Guile does things in 
a cleaner way, once one figures out how to do them in the first place. One thing 
I really like are the ports. Stuff like call-with-output-string. Takes some 
twisting of the brain, but once one gets it, it becomes very useful and elegant.

But yes, Python is very beginner friendly in terms of batteries included. 
Although I think that its syntax feels a bit ad-hoc. As in "Oh we want some 
syntax for X … lets invent this keyword here." or some new operators or things 
like that. I like Guile syntax (or Scheme in general) much more. However, it is 
difficult to motivate others in a quick demo to learn the language, when you 
cannot take half an hour time to explain, what that for other people weird 
looking syntax is actually really cool.

Regards,
Zelphir

-- 
repositories: https://notabug.org/ZelphirKaltstahl