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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Get-system-command-output/Racket/get-system-command-output.rkt Normal file
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#lang racket/base
(require racket/system
(only-in racket/port with-output-to-string)
tests/eli-tester)
(test
;; system runs command and outputs to current output port (which is stdout unless we catch it)
(system "ls /etc/motd") => #t
;; it throws an error on non-zero exit code (so I need to catch it in this error handler)
(system "false") => #f ; nothing printed to stdout/stderr
(system "ls /etc/mosh") => #f ; error report printed to stderr
;; output can be captured by redirecting stdout/stderr (which are known as current-output-port and
;; current-error-port in racket parlance).
;; the command printed a \n, so there is a newline captured by the system command
(with-output-to-string (λ () (system "ls /etc/motd"))) => "/etc/motd\n"
;; no \n is captured when none is captured
(with-output-to-string (λ () (system "echo -n foo"))) => "foo"
;; error is still not captured (it's still printed to stderr)
(with-output-to-string (λ () (system "echo -n foo; echo bar 1>&2"))) => "foo"
;; we can capture both with:
(let* ((out-str-port (open-output-string))
(err-str-port (open-output-string))
(system-rv
(parameterize ((current-output-port out-str-port) (current-error-port err-str-port))
(system "echo -n foo; echo bar 1>&2"))))
(values system-rv (get-output-string out-str-port) (get-output-string err-str-port)))
=> (values #t "foo" "bar\n"))