how to get return value of process called with windows’ “start” cmd command?

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in my python script i have several threads calling an application with subprocess like this:

arguments = ["start", "/min", "/w", "program", "prog_argument_1", "prog_argument_2", "etc"]
proc = subprocess.run(arguments , text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)

i am calling the program with “start /min /w” so each execution has its own cmd window and i can bring it up to see the status or if it hung up somewhere or wants user input
however by doing so the retun value is always zero and the standard output and error are always empty, regardless of what the programm did. to improve my script and for successive operations i would like to recover them.

i tried doing like this

arguments = ["program", "prog_argument_1", "prog_argument_2", "etc"]
proc = subprocess.run(arguments , text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)

in this case i have all the information i need in the proc variable but then the program is executed silently and if it hangs up or takes a long time i have no way to check what’s going on

looked up Popen after comments, now by doing

proc = subprocess.run(arguments , text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)

i do get a separate window and stout/stderr but the new window has no text printed on it, likewise if i call Popen without redirecting stout and err to pipes

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    The subprocess module is a Python wrapper module for calling on Windows the Windows kernel library function CreateProcess with a STARTUPINFO structure. shell=True means calling CreateProcss to run the executable defined by the environment variable ComSpec which is defined with %SystemRoot%\System32\cmd.exe on Windows.

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    The internal command START of the Windows Command Processor cmd.exe is for starting an executable for parallel execution to cmd.exe by calling CreateProcess by cmd.exe for the executable to run. It can be seen here that the entire solution used by you does not make much sense. Why should python.exe call CreateProcess to run cmd.exe which is instructed to call CreateProcess to run another executable? The executable to run parallel to python.exe can be started directly with subprocess.Popen() for running parallel to python.exe with a visible console window.

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    It is even possible to define in the Python script on using subprocess.Popen() the parameters for the console window, i.e. the position on screen, the height and the width. That is all not possible on running cmd.exe for starting an executable using its internal command start because of the command start is very limited in its options for calling CreateProcess in comparison to subprocess.Popen(). The solution for your XY problem is therefore going back a step, read the three referenced documentation pages, and rewrite the Python script code.

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  • BTW: What are the ERRORLEVEL values set by internal cmd.exe commands? explains what the internal command START of cmd.exe returns to cmd assigned to its dynamic variable ERRORLEVEL of which value is returned on self-closing of cmd.exe to the parent process. The exit code is 0 on start could successfully start the application, i.e. CreateProcess returned a nonzero value (TRUE).

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  • The application started with command START gets from CreateProcess its own standard input, standard output and standard error handles. The standard output and standard error of cmd.exe is for that reason always empty on successfully starting the executable. Standard error would be only not empty on CreateProcess fails to find the executable to run as separate process (not fully detached but as child process in this case because of using start option /w). What you want to achieve is impossible as long as using subprocess.Run with shell=True and with cmd internal start.

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