run a sh shell while clicking button in QML with QT5.15.0

lxy12345

Hi all
I have google a lot about how to run a shell while clicking button in qml but those topics are too old such like 2013 or 2014 with qquick 1.0. The codes in main.cpp are totally different with those and header files as well.
Could anyone give me a new demo code about how to run shell?
Thanks

sierdzio

What do you mean by "run shell"? What are you trying to achieve?

If you want to run an external process, use QProcess. If you want to show a terminal inside your app, it will be harder. You can probably use KDE's frameworks to get a Konsole inside your app, like Dolphin, Yakuake and others do.

lxy12345

Hi, I just want to run an external process which is just a binary file. I write a shell script to run that binary file and want to run this shell while clicking the button in QML.
Do you have any demo codes?

mrjj

@lxy12345
Hi
did you try
http://71.254.128.33/qml/process.html

lxy12345

@mrjj Hi, I followed your post but an error occured.
I copied the process.h file.
Here below is my main.cpp:
#include <QGuiApplication>
#include <QQuickView>
#include <QQmlEngine>
#include <QtQml>
#include "process.h"

int main(int argc, char* argv[])
{
QGuiApplication app(argc,argv);
QQuickView view;
view.setResizeMode(QQuickView::SizeRootObjectToView);
// Qt.quit() called in embedded .qml by default only emits
// quit() signal, so do this (optionally use Qt.exit()).
QObject::connect(view.engine(), &QQmlEngine::quit,
qApp, &QGuiApplication::quit);
qmlRegisterType<Process>("Process",1,0,"Process");

view.setSource(QUrl("qrc:///main.qml"));
//view.resize(1000, 480);
view.show();
return app.exec();

}

Here below is my qml file:
Item {
id: usbcam2
signal clicked
x:10
y:450
width : 140
height: 70

    BorderImage {
        id: buttonImage2
        source: "images/toolbutton.sci"
        width: usbcam2.width
        height: usbcam2.height
    }
    MouseArea {
        id: mouseRegion2
        anchors.fill: buttonImage2
        onClicked: process.start("/bin/cat", [ "/proc/uptime" ]);
    }
    Text {
        id: btnText2
        anchors.fill: buttonImage2
        anchors.margins: 5
        text: "USBcam2"
        horizontalAlignment: Text.AlignHCenter
        verticalAlignment: Text.AlignVCenter
        elide: Text.ElideRight
        color: "white"
        font.bold: true
        style: Text.Raised
        styleColor: "black"
        font.pixelSize: 14
    }

}

}

When I click the button, the error showed:
qrc:/main.qml:99: ReferenceError: process is not defined
what's that meanning?

ODБOï

@lxy12345 said in run a sh shell while clicking button in QML with QT5.15.0:

Here below is my qml file:

you did not create a Process item

 Process {
        id: process     
    }

lxy12345

@LeLev I don't really understand this code:
onReadyRead: text.text = readAll();
Is onReadyRead a signal? or something like onCliked in button?

jsulm

@lxy12345 said in run a sh shell while clicking button in QML with QT5.15.0:

Is onReadyRead a signal?

yes

lxy12345

@jsulm Hi, jsulm. I have tried your post but I misunderstand somewhere maybe.
I don't understand the singal "onReadyRead", I googled which said that this signal is for TCP/IP??? I am not very sure about that.
what and where should I modify in your post?

mrjj

@lxy12345 said in run a sh shell while clicking button in QML with QT5.15.0:

onReadyRead

Hi
Its also for other things.
" QProcess emits readyRead() when data is available on the current read channel. It also emits readyReadStandardOutput() when new standard output data is available"

https://doc.qt.io/qt-5/qprocess.html
in the Communicating via Channels section

lxy12345

@jsulm when I tried the code ,
Text {
id: text
}

Process{
    id: process
     onReadyRead: text.text = readAll();
}
Timer {
     interval: 10
     repeat: true
     triggeredOnStart: true
     running: true
     onTriggered: process.start("/bin/cat", [ "/proc/uptime" ]);
 }

it outputs:
QProcess::start: Process is already running
QProcess::start: Process is already running
QProcess::start: Process is already running
QProcess::start: Process is already running
QProcess::start: Process is already running
QProcess::start: Process is already running
QProcess::start: Process is already running
QProcess::start: Process is already running

I think that the shell here is just "cat /proc/uptime", it should output some numbers.
Maybe I should read and understand Qprocess class first?

JonB

@lxy12345
I don't know anything about QML, but

QProcess::start: Process is already running

means that you have a QProcess instance where you have set of a start() but it has not yet completed and you have not waited for it, and now you're trying to set off a new start(). You either need to wait for completion of the process instance, or you need to use a new instance of QProcess each time. As I say, i don't know QML how to do that, but that's the cause/reason.

mrjj

Hi
Since you set the timer to repeat, it will start a new QProcess each time and
10 ms might be too short. try raising it so the other Qprocess gets change to finished.

Timer {
interval: 10
repeat: true

JonB

@mrjj
Really it ought have a handler for "process finished" signal, to be robust. I don't know how you do that from QML.

OP might have a go at the naughty:

     onTriggered: process.start("/bin/cat", [ "/proc/uptime" ]); process.waitForFinished();

with all the caveats. I don't know if that would work simpler.

mrjj

@JonB
Yes i agree as guessing on execution time is bound to fail in many other cases.

lxy12345

@mrjj finally, I found the reason. I should add console.log() to show output . The post is correct, thanks guys

JonB

@lxy12345 said in run a sh shell while clicking button in QML with QT5.15.0:

The post is correct

What post is correct?

lxy12345

@JonB http://71.254.128.33/qml/process.html This post.

JonB

@lxy12345
Ah, I see. Yes, that looks reasonable. However, it has no code for waiting for the QProcess::finished signal. I admitted earlier I do not know how QML works with regard to instances. But if it does not create new QProcess instances, and if you re-use the one instance before the cat OS command has completed, you will get the QProcess::start: Process is already running error you showed earlier. Since the /bin/cat /proc/uptime completes "quickly" you may get away with it for a while.

You may well be using this as just an example to play with QProcess, I don't know. But be aware that if you are really trying to do /bin/cat /proc/uptime , that is a waste of time! All that does is an OS command to read the contents of the file. You would be better doing this by just opening the file /proc/uptime and reading its content from QML, without any QProcess OS command at all.

lxy12345

@JonB thanks for replying me. The "cat /proc/uptime" cmd is just an example. I change the cmd in my project, I use this code to open a shell which controls some peripherals.