# How to use subprocess **URL:** \ **Category:** Questions & Answers\ **Tags:** system\ **Created:** [October 24, 2025, 9:35pm UTC](https://racket.discourse.group/t/how-to-use-subprocess/3982 "2025-10-24T21:35:55Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![AndreMayers](https://avatars.discourse-cdn.com/v4/letter/a/ecccb3/32.png) [@AndreMayers](https://racket.discourse.group/u/AndreMayers)\ **Post date:** [October 24, 2025, 9:35pm UTC](https://racket.discourse.group/t/how-to-use-subprocess/3982/1 "2025-10-24T21:35:55Z")
In the following code, st-out is always `#f`. Why? I tried several variants of the following code. ```scheme (set st-in (open the output file "out-file.txt")) (set st-out (open input file "in-file.txt" )) (define-values (newprocess stdout stdin stderr ) (sub-process st-in st-out #f "C: WINDOWS system32 cmd.exe" "type" "C: Users Andre tobdeleted costco.txt")) stdout (printf "stdout: n~a" (port->string stdout)) ``` I want to do the same thing as ```scheme (define command-cmd (string-append " "C: WINDOWS system32 cmd.exe " " /c" " type" " C: Users Andre tobdeleted costco.txt" )) (define resul-brut-cmd (with-output-to-string (lambda () (system command-cmd) ))) ``` ---
**Author:** ![bakgatviooldoos](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/bakgatviooldoos/32/1381_2.png) [@bakgatviooldoos](https://racket.discourse.group/u/bakgatviooldoos)\ **Post date:** [October 25, 2025, 1:20am UTC](https://racket.discourse.group/t/how-to-use-subprocess/3982/2 "2025-10-25T01:20:26Z")
Hi, @AndreMayers. From the docs, we see the following: > The [subprocess](https://docs.racket-lang.org/reference/subprocess.html#%28def._%28%28quote._~23~25kernel%29._subprocess%29%29) procedure returns four values: > > - a subprocess value representing the created process; > - an input port piped from the process’s standard output, or #f if stdout was a port; > - an output port piped to the process’s standard input, or #f if stdin was a port; > - an input port piped from the process’s standard error, or #f if stderr was a port or 'stdout. So, because you _provide_ ports for `stdout` and `stdin`, the corresponding values returned by `subprocess` are false. Compare to the example they give at the end of that section: ```scheme (define-values (sp out in err) (subprocess #f #f #f "/bin/ls" "-l")) (printf "stdout:\n~a" (port->string out)) (printf "stderr:\n~a" (port->string err)) (close-input-port out) (close-output-port in) (close-input-port err) (subprocess-wait sp) ``` Happy hacking! ---
**Author:** ![AndreMayers](https://avatars.discourse-cdn.com/v4/letter/a/ecccb3/32.png) [@AndreMayers](https://racket.discourse.group/u/AndreMayers)\ **Post date:** [October 25, 2025, 1:00pm UTC](https://racket.discourse.group/t/how-to-use-subprocess/3982/3 "2025-10-25T13:00:30Z")
[quote="bakgatviooldoos, post:2, topic:3982"] `"/bin/ls"` May be I don't understand something more profound. Where can I see the result of "/bin/ls" ? The following code is almost the same as yours but for Windows 11 (define-values (sp out in err) (subprocess #f #f #f "C: WINDOWS system32 cmd.exe" "dir" )) (printf "stdout:\n~a" (port-\>string out)) (printf "stderr:\n~a" (port-\>string err)) (close-input-port out) (close-output-port in) (close-input-port err) (subprocess-wait sp) Where I can I see the directory list ? ---
**Author:** ![bakgatviooldoos](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/bakgatviooldoos/32/1381_2.png) [@bakgatviooldoos](https://racket.discourse.group/u/bakgatviooldoos)\ **Post date:** [October 25, 2025, 4:35pm UTC](https://racket.discourse.group/t/how-to-use-subprocess/3982/4 "2025-10-25T16:35:03Z")
Apologies if I was being confusing, the example I used, is for a Linux machine. Hmm, I am not sure what is the matter with `cmd.exe`. It's probably just that I am being stupid about how ports work here because I can `read` from the port, but it seems to hang when I try your code. I am also running Windows 11 on my machine. If I use `powershell.exe` instead, it seems to work: ```scheme #lang racket (define-values (sp out in err) (subprocess #f #f #f "C:/WINDOWS/System32/WindowsPowerShell/v1.0/powershell.exe" "dir")) (printf (port->string out)) (printf (port->string err)) (close-input-port out) (close-output-port in) (close-input-port err) (subprocess-wait sp) ``` ```scheme Directory: C:\Users\CHRISTIAAN-BRAND\racket\racket-discourse Mode LastWriteTime Length Name ---- ------------- ------ ---- dar--l 2025/05/08 14:46 advent-2024 d----- 2025/07/19 00:37 ddrake-wires-lang -a---- 2025/10/25 03:01 323 andremayers-subprocess.bak -a---- 2025/10/25 18:22 272 andremayers-subprocess.rkt -a---l 2024/11/06 15:48 207 andy-generics.bak -a---l 2024/11/06 16:05 207 andy-generics.rkt -a---- 2025/07/23 02:04 5642 booklet.txt -a---- 2025/09/09 22:49 429 damien-mattei-defform.bak.bak -a---- 2025/09/10 00:49 429 damien-mattei-defform.bak.scrbl -a---l 2024/11/23 15:13 635 damien-mattei-regex-hashbang.rkt . . . ``` ---
**Author:** ![AndreMayers](https://avatars.discourse-cdn.com/v4/letter/a/ecccb3/32.png) [@AndreMayers](https://racket.discourse.group/u/AndreMayers)\ **Post date:** [October 25, 2025, 5:48pm UTC](https://racket.discourse.group/t/how-to-use-subprocess/3982/5 "2025-10-25T17:48:37Z")
Thank you. You show me that it works on the standard output port. It help me to pinpoint the problem. I am shy to tell it. I didn't close outport port. Here is the code that works. (current-directory "C:\Users\Andre\tobedeleted") (define st-in (open-output-file "out-file.txt")) (define st-out (open-input-file "in-file.txt" #:mode 'text )) (define-values (sp out in err) (subprocess st-in st-out #f "C:/WINDOWS/System32/WindowsPowerShell/v1.0/powershell.exe" "dir")) (printf (port-\>string st-out)) (printf (port-\>string err)) (close-input-port st-out) (close-output-port st-in) (close-input-port err) (subprocess-wait sp)