How to use Windows QT to call WSL cmd?

[JonB]

@NTU_WTY
That looks worrying to me! Whatever it's supposed to be, the fact that something is even echoing back 'C:\\Windows\\System32\\wsl.exe' ... looks like some kind of error to me....

I have asked several times what exactly you tested in Command Prompt....

Oh, and a huge "BTW" when you do use the redirection and say res.txt is still empty: where are you looking, what do you think the current working directory of your Qt app is? Have you checked with specifying an absolute path?

Please stop trying the redirection for a while, it only complicates. Try one of these:

• sh.start("cmd", QStringList() << "/c" << "C:\\Windows\\System32\\wsl.exe ls");
• sh.start("C:\\Windows\\System32\\wsl.exe", QStringList() << "ls");

Especially the second one. I would not use waitFor..., at least while I diagnosed, I would use the signals/slots including for errors, as I wrote earlier.

[NTU_WTY]

No error shows after writing in QStringList, not as it would show: "wsl is not recognized as an internal or external command" when writing in my original QProcess::execute way.`

What do you mean by this? If you are saying you originally used QProcess::execute("C:\\Windows\\System32\\wsl.exe", ...) or "wsl" or "cmd /c ..." or whatever and got "wsl is not recognized as an internal or external command" then please show what exact command you did that way.

QProcess::execute("cmd /c wsl ls")
QProcess::execute("cmd /c C:/Windows/System32/wsl.exe ls");
I wrote in above ways that both not recognized wsl. But if I open the cmd prompt, power shell, or MinGW terminal, they all recognize wsl.

About the following two lines:

• sh.start("cmd", QStringList() << "/c" << "C:\\Windows\\System32\\wsl.exe ls");
• sh.start("C:\\Windows\\System32\\wsl.exe", QStringList() << "ls");

They will get false returned from waitForFinished immediately. But the readAllStandardError() shows empty. (Previous true also immediately. Not sure what does that mean...)
Sorry I don't know how to "hook up all signals from QProcess". Can you give me more hint when you have time? Thank you very much.

[JonB]

@NTU_WTY said in How to use Windows QT to call WSL cmd?:

I wrote in above ways that both not recognized wsl. But if I open the cmd prompt, power shell, or MinGW terminal, they all recognize wsl.

Then you have a problem. This is my final time of asking: copy and paste, or show me a screenshot, of precisely what you are trying in a Command Prompt. Do not tell me "they work", show me what you are trying, character for character.

Sorry I don't know how to "hook up all signals from QProcess"

At minimum connect a slot to void QProcess::errorOccurred(QProcess::ProcessError error):

• Make your QProcess sh; a class member variable, at least temporarily, so it stays in scope.
• Start with: connect(&sh, &QProcess::errorOccurred, this, [](QProcess::ProcessError error) { qDebug() << error; }), we'll see whether we need any further ones depending on that.

[NTU_WTY]

@JonB said in How to use Windows QT to call WSL cmd?:

@NTU_WTY said in How to use Windows QT to call WSL cmd?:

I wrote in above ways that both not recognized wsl. But if I open the cmd prompt, power shell, or MinGW terminal, they all recognize wsl.

Then you have a problem. This is my final time of asking: copy and paste, or show me a screenshot, of precisely what you are trying in a Command Prompt. Do not tell me "they work", show me what you are trying, character for character.

[JonB]

@NTU_WTY
So all you have proved is that wsl ls works from that Command Prompt. Which is not the same as the command you are trying to issue from your Qt program, is it? Maybe it's wsl.exe, maybe it's not. Maybe it's in C:\Windows\System32, maybe it's not.

Will you please try:

cmd /c "C:\Windows\System32\wsl.exe ls"

in a Command Prompt.

After that, try the error code I showed earlier.

[NTU_WTY]

@JonB
Sorry that I choose the wrong terminal. The following is my "C:\Windows\System32\wsl.exe" result:

If I directly type: cmd /c "C:\Windows\System32\wsl.exe ls" in the search input, the terminal will flash out (successfully show and close). So I modified to: cmd /k "C:\Windows\System32\wsl.exe ls" , it opens the terminal and lists all the files inside.
I also tried: cmd /k "C:\Windows\System32\wsl.exe pwd", and it returns ,
where /mnt/c is the correct representation of the path C:\ in wsl.

About the slot, I think I need more time to digest, thank you~

[JonB]

@NTU_WTY said in How to use Windows QT to call WSL cmd?:

If I directly type: cmd /c "C:\Windows\System32\wsl.exe ls" in the search input

In what "search input"? The Windows desktop Start button area, or similar? I asked you to type into a Command Prompt...! Never mind, I get the gist, it looks like the full path does work, that in itself is not the issue.

Yes you should try the code with signal/slot I showed earlier.

You might also try e.g.

sh.start("cmd", QStringList() << "/c" << "echo Hello >> C:\\Temp\\tempfile.txt");

Please be sensible about the path, whatever works for you. Does this work?

[NTU_WTY]

@JonB said in How to use Windows QT to call WSL cmd?:

You might also try e.g.
sh.start("cmd", QStringList() << "/c" << "echo Hello >> C:\Temp\tempfile.txt");

Please be sensible about the path, whatever works for you. Does this work?

Yes! It generates tempfile and also Hello inside this file. It only fails when related to wsl.

I try to rewrite the code by mimicking from the doc:

QObject *parent;
QString program = "cmd";
QStringList arguments;
arguments << "/c" << "C:\\Windows\\System32\\wsl.exe" << "ls"; 
QProcess *sh = new QProcess(parent);
sh->start(program, arguments);

connect(sh, &QProcess::errorOccurred, this, [](QProcess::ProcessError error) { qDebug() << error; });

It outputs this when the object is created:
21:17:42: C:/Users/USER/Documents/Code/Qt/build-testQT-Desktop_Qt_5_15_2_MinGW_32_bit-Debug/debug/testQT.exe crashed.
I'm not sure if I wrote it right. Thank you for your patience~ Please correct me and give me more hints!

[jsulm]

@NTU_WTY said in How to use Windows QT to call WSL cmd?:

QObject *parent;

This is dangling pointer!
If you do not need a parent then pass nullptr instead!

QProcess *sh = new QProcess();

If you really want a proper parent then pass a pointer to an existing (allocated) object.

[NTU_WTY]

@jsulm said in How to use Windows QT to call WSL cmd?:

This is dangling pointer!
If you do not need a parent then pass nullptr instead!
QProcess *sh = new QProcess();

If you really want a proper parent then pass a pointer to an existing (allocated) object.

Thank you~ The code executed successfully without any messages after null ptr correction. So... what shall I do next to get some info from the process?

[JonB]

@NTU_WTY said in How to use Windows QT to call WSL cmd?:

what shall I do next to get some info from the process?

So connect(&sh, &QProcess::errorOccurred, this, [](QProcess::ProcessError error) { qDebug() << error; }) does not lead to any output now when you run the wsl subprocess?

[NTU_WTY]

@JonB said in How to use Windows QT to call WSL cmd?:

So connect(&sh, &QProcess::errorOccurred, this, [](QProcess::ProcessError error) { qDebug() << error; }) does not lead to any output now when you run the wsl subprocess?

No, no output. Actually I wrote: connect(sh, &QProcess::errorOccurred, this, [](QProcess::ProcessError error) { qDebug() << error; }); since &sh will get error.

[JonB]

@NTU_WTY
I would connect QProcess::stateChanged() next.

[NTU_WTY]

@JonB said in How to use Windows QT to call WSL cmd?:

I would connect QProcess::stateChanged() next.

I modified the connect line to:

connect(sh, &QProcess::stateChanged, this, [](QProcess::ProcessState newState) { qDebug() << newState; });

It outputs: QProcess::NotRunning

[JonB]

@NTU_WTY
Have you put this connect() (indeed any/all connect()s) before your sh->start(program, arguments);? We want this signal connected and reporting before it attempts to start the program.

[NTU_WTY]

@JonB OK, now it outputs three lines:

• QProcess::Starting
• QProcess::Running
• QProcess::NotRunning

[JonB]

@NTU_WTY
So that implies it did start, then ran and stopped running (i.e. finished). I suspect the whole thing is working, it is not evident what "proof" you have that it is not.

QProcess *sh = new QProcess(parent);
connect(sh, &QProcess::errorOccurred, this, [](QProcess::ProcessError error) { qDebug() << error; });
connect(sh, &QProcess::stateChanged, this, [](QProcess::ProcessState newState) { qDebug() << newState; });
connect(sh, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
    [=](int exitCode, QProcess::ExitStatus exitStatus){ qDebug() << exitCode << exitStatus; });
connect(sh, &QProcess::readyReadStandardError, this, [=]() { qDebug() << "stderr:" << sh->readAllStandardError(); });
connect(sh, &QProcess::readyReadStandardOutput, this, [=]() { qDebug() << "stdout:" << sh->readAllStandardOutput(); });

sh->start(program, arguments);

It is now up to you to test with various parameters for program and arguments. For example

sh->start("cmd", QStringList() << "/c" << "dir");

should test that the above code is working as you would expect.

sh->start("C:\\Windows\\System32\\wsl.exe", QStringList() << "--help");

should prove that wsl runs, it should report back its "usage".

sh->start("C:\\Windows\\System32\\wsl.exe", QStringList() << "ls");

should get your wsl to do an ls and output whatever that outputs, provided wsl allows you do that (I would not know if there is some issue there).

[NTU_WTY]

@JonB Thank you so much. Do I need to set parent as nullptr? And the readyReadStandardError and readyReadStandardOutput would get error so I comment them first. Here's the code I slightly modified:

QProcess *sh = new QProcess();
connect(sh, &QProcess::errorOccurred, this, [](QProcess::ProcessError error) { qDebug() << error; });
connect(sh, &QProcess::stateChanged, this, [](QProcess::ProcessState newState) { qDebug() << newState; });
connect(sh, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),[=](int exitCode, QProcess::ExitStatus exitStatus){ qDebug() << exitCode << exitStatus; });
//connect(sh, &QProcess::readyReadStandardError, this, [sh]() { qDebug() << "stderr:" << readAllStandardError(); });
//connect(sh, &QProcess::readyReadStandardOutput, this, [sh]() { qDebug() << "stdout:" << readAllStandardOutput(); });

QString program = "cmd";
QStringList arguments;
arguments << "/c" << "dir" << ">>" << "C:\\Temp\\dir_res.txt";
//arguments << "/c" << "C:\\Windows\\System32\\wsl.exe" << "ls" << ">>" << "C:\\Temp\\ls_res.txt";
sh->start(program, arguments);

The dir command successfully list the files in dir_res.txt with Qt output as:

• QProcess::Starting
• QProcess::Running
• QProcess::NotRunning
• 0 QProcess::NormalExit

The wsl command still creates empty file in ls_res.txt with Qt output as:

• QProcess::Starting
• QProcess::Running
• QProcess::NotRunning
• 1 QProcess::NormalExit

if I change the program directly to "C:\\Windows\\System32\\wsl.exe", the output is:

• QProcess::Starting
• QProcess::NotRunning
• QProcess::FailedToStart

[JonB]

@NTU_WTY said in How to use Windows QT to call WSL cmd?:

Do I need to set parent as nullptr?

Doesn't matter (for our purposes), this might be a better choice.

And the readyReadStandardError and readyReadStandardOutput would get error so I comment them first.

No, you are not supposed to comment them out, you are supposed to make them work. Preferably on your own, if you want my help please don't say they "get error", copy & paste the line and the error message. Or do you expect someone to guess what the issue is rather than you doing that?

I seem to have to repeat myself. Can you please start by doing as I ask, with code working and my commands. Don't start doing your own commands till those are resolved. I have said we need to get behaviour we understand first before you introduce redirection. Can you please do the 3 commands I wrote, and report the output, before you do your own variations. And you must get the connect(sh, &QProcess::readyRead...s working for these....

[NTU_WTY]

@JonB said in How to use Windows QT to call WSL cmd?:

&QProc

The error is: Use of undeclared identifier 'readAllStandardError'
I tried this way to make it work (please correct me if I'm wrong):

connect(sh, &QProcess::readyReadStandardError, this, [sh]() { qDebug() << "stderr:" << sh->readAllStandardError(); });
connect(sh, &QProcess::readyReadStandardOutput, this, [sh]() { qDebug() << "stdout:" << sh->readAllStandardOutput(); });

After this modification, the output of sh->start("C:\\Windows\\System32\\wsl.exe", QStringList() << "--help"); is:

• QProcess::Starting
• QProcess::NotRunning
• QProcess::FailedToStart

same as the output of sh->start("C:\\Windows\\System32\\wsl.exe", QStringList() << "ls");

The output of sh->start("cmd", QStringList() << "/c" << "dir"); is:

QProcess::Starting
QProcess::Running
stdout: " \xBA\xCF\xBA\xD0\xB0\xCF C \xA4\xA4\xAA\xBA\xBA\xCF\xBA\xD0\xA8S\xA6\xB3\xBC\xD0\xC5\xD2\xA1""C\r\n \xBA\xCF\xBA\xD0\xB0\xCF\xA7\xC7\xB8\xB9:  4E94-6F25\r\n\r\n C:\\Users\\USER\\Documents\\Code\\Qt\\build-testQT-Desktop_Qt_5_15_2_MinGW_32_bit-Debug \xAA\xBA\xA5\xD8\xBF\xFD\r\n\r\n"
stdout: "2022/08/30  \xA4U\xA4\xC8 03:26    <DIR>          .\r\n2022/08/30  \xA4U\xA4\xC8 03:26    <DIR>          ..\r\n2022/08/23  \xA4U\xA4\xC8 06:37               985 .qmake.stash\r\n2022/08/23  \xA4U\xA4\xC8 04:29    <DIR>          .qtc_clangd\r\n2022/08/30  \xA4U\xA4\xC8 06:29    <DIR>          debug\r\n2022/08/24  \xA4W\xA4\xC8 09:43            27,314 Makefile\r\n2022/08/24  \xA4W\xA4\xC8 09:43            36,629 Makefile.Debug\r\n2022/08/24  \xA4W\xA4\xC8 09:43            36,723 Makefile.Release\r\n"
stdout: "2022/08/23  \xA4U\xA4\xC8 06:37    <DIR>          release\r\n2022/08/29  \xA4U\xA4\xC8 03:04                 0 res.txt\r\n2022/08/24  \xA4W\xA4\xC8 10:13    <DIR>          Test\r\n2022/08/24  \xA4W\xA4\xC8 09:43             2,976 ui_mainwindow.h\r\n2022/08/29  \xA4U\xA4\xC8 03:55                 0 usersuserappdatalocaltemptmp1ia32l\r\n2022/08/30  \xA4U\xA4\xC8 03:26                 0 usersuserappdatalocaltemptmp1raevz\r\n2022/08/29  \xA4U\xA4\xC8 04:50                 0 usersuserappdatalocaltemptmp6vdzgw\r\n2022/08/24  \xA4W\xA4\xC8 09:45                 0 usersuserappdatalocaltemptmpc2kqux\r\n2022/08/29  \xA4U\xA4\xC8 09:05                 0 usersuserappdatalocaltemptmpdaqef2\r\n2022/08/24  \xA4W\xA4\xC8 10:02                 0 usersuserappdatalocaltemptmpeilcjn\r\n2022/08/29  \xA4U\xA4\xC8 03:51                 0 usersuserappdatalocaltemptmpfppfsf\r\n2022/08/29  \xA4U\xA4\xC8 10:06                 0 usersuserappdatalocaltemptmphst0vl\r\n2022/08/29  \xA4W\xA4\xC8 11:18                 0 usersuserappdatalocaltemptmpmxin8w\r\n2022/08/26  \xA4W\xA4\xC8 08:19                 0 usersuserappdatalocaltemptmppjmq8y\r\n2022/08/29  \xA4U\xA4\xC8 10:08                 0 usersuserappdatalocaltemptmpxs1ja2\r\n2022/08/29  \xA4U\xA4\xC8 03:15                 0 usersuserappdatalocaltemptmpypomgz\r\n              18 \xAD\xD3\xC0\xC9\xAE\xD7         104,627 \xA6\xEC\xA4\xB8\xB2\xD5\r\n"
stdout: "               6 \xAD\xD3\xA5\xD8\xBF\xFD  597,839,917,056 \xA6\xEC\xA4\xB8\xB2\xD5\xA5i\xA5\xCE\r\n"
QProcess::NotRunning
0 QProcess::NormalExit