An hour and a half ago, Neil Van Dyke wrote:
> I'd put those port close calls in a "dynamic-wind" cleanup thunk.
> I'd also catch the exceptions that could be raised by the
> port-closing procedure itself in the cleanup thunk. And I'd make
> sure that any custodian I was using didn't close the ports at the
> wrong time for me.
More conveniently:
(with-output-to-string (λ() (system "whatever")))
> Regarding I/O, I'd make stdin a null port so that the process wouldn't
> block (unless I actually had to feed it input). [...]
Yes:
(parameterize ([current-input-port (open-input-string "")])
(with-output-to-string (λ() (system "whatever"))))
> I also prefer to use "process*" over "process", because it
> eliminates some possible command line assembling errors (especially
> quoting and escaping) and eliminates resulting exploits. (I'll just
> assert here that most people who assemble command lines as single
> strings using variables do it wrong and potentially create security
> exploits or accidents.)
And that's a very good point -- IMO, string concatenation is good only
for quick uses with a known simple string (ie, no uses that assemble
strings).
I often end up with a little utility for that, something like:
(define (make-exe name)
(define (->string x) (if (string? x) x (format "~a" x)))
(define exe (find-executable-path (->string name)))
(unless exe (error 'make-exe "could not find executable: ~e" name))
(λ args (apply system* exe (map ->string args))))
(define-syntax-rule (define-exe name) (define name (make-exe 'name)))
(define-exe echo)
(echo 1 'foo "bar")
And that can be extended with keywords as needed, for returning a
string, cleaning it from it's terminating newline and/or splitting by
newlines, having an empty input, running asynchronously with a
callback, specifying input/output files, etc etc etc.
(It's probably a good idea to add something like that to
`racket/system', but the huge number of possibilities made it easier
to just write a specific wrapper whenever I need one...)
--
((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
http://barzilay.org/ Maze is Life!
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