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How we can run Linux command from qt code?



  • Hi everyone;
    I want to run the Linux command from qt code . I did following code to run the command but it is not executing my command.

    QString ab = "cd  /sys/bus/iio/devices/iio:device1 && echo 24250000 > out_altvoltage1_TX_LO_frequency"
    QProcess p;
    p.startDetached("/bin/bash", QStringList()<<"-c"<<ab);
    

    Thanks in advance!


  • Lifetime Qt Champion

    @Wasee Why do you want to use a process to read from a device file?
    Simply read that file using QFile like any other file.



  • @jsulm Thanks for your reply!
    I want write this command on device from qt code. I code in following way.

    QString ab = "cd /sys/bus/iio/devices/iio\:device1 && echo  ";
    
    QString ad = " > out_altvoltage1_TX_LO_frequency";
                                  ab.append(24250000);
    QProcess on;
    on.start(ab.append(ad));
    on.waitForFinished(-1);
    qDebug() << "TX_LO ="<<ab;
    QProcess p;
    p.startDetached("/bin/bash", QStringList()<<"-c"<<ab);
    

    I made command successfully but not running on device through qt.


  • Lifetime Qt Champion

    @Wasee Can you please explain why you need to read the /sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency file using an addional process?
    As I told you already you can read this file in your Qt app using QFile...

    Also, why do you start TWO processes now?!



  • @jsulm thanks;
    I passed the RX_LO_frequency to the device via bashscript using QProcess when I connect the device with a signal generator from the external at this time my device sense according to the value I passed in RX_LO_frequency. Now I want to pass the same value on TX_LO_frequency using QProcess this is the main reason I am using QProcess.
    thanks


  • Lifetime Qt Champion

    @Wasee I still fail to understand the need for QProcess.
    You can do all this using QFile way more efficiently.
    But it is up to you...



  • @jsulm thanks;
    kindly give me any suitable example QFile device read.
    thanks


  • Lifetime Qt Champion

    @Wasee said in How we can run Linux command from qt code?:

    kindly give me any suitable example QFile device read

    What example?
    These device files are files, so you read/write them like any other files...



  • @Wasee
    To answer your original question: the code you showed in your first example should do exactly what you say you want it to do --- provided you have first typed that command into a bash shell to verify it works correctly. So how do you know "it is not executing my command"? There is no need to run it startDetached() instead of plain start(). You could then capture any error and anything written to stdout/stderr ot check for anything unexpected. [Note: your literal string has \: in it. That is not right for C++. Either \\: or just simple :. Maybe that is why it had problems.]

    However, as @jsulm said this command simple writes a string to a file. So no need for a QProcess, what is wrong with:

    QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
    if (f.open(QIODevice::WriteOnly))
    {
        qint64 count = f.write("24250000");
        Q_ASSERT(count > 0);
        f.close();
    }
    


  • @JonB Hi;
    I coded as you suggested above but still not changing TX_LO_frequency value. why?
    thanks


  • Lifetime Qt Champion

    @Wasee Did you do what @JonB mentioned: "provided you have first typed that command into a bash shell to verify it works correctly"?
    So, does it work if you do it in terminal?


  • Lifetime Qt Champion

    This post is deleted!


  • @Wasee said in How we can run Linux command from qt code?:

    but still not changing TX_LO_frequency value. why?

    Did you even at least check the return result of the open() for yourself? For all I know you do not have permission to write to that file. This is part of what doing development involves....

    @jsulm

    Also I would not write a string but a number:

    That's fine, but it's not what the OP's echo 24250000 > out_altvoltage1_TX_LO_frequency would do (treat anything as a number), which I was trying to copy. In fact I think Linux echo will append a newline, so the OP may need to do that too.



  • @JonB said in How we can run Linux command from qt code?:
    echo 24250000 > out_altvoltage1_TX_LO_frequency this command run in terminal and change the value on device. But not changing from qt code.


  • Lifetime Qt Champion

    @Wasee said in How we can run Linux command from qt code?:

    change the value on device

    Without sudo?

    Please add error handling to your code: print error message if f.open(...) fails.



  • @jsulm Hi;
    Yes without sudo in terminal its changing value. No error of device open its not returning.
    thanks



  • @Wasee

    • Did you add the error checking code I advised?
    • Did you try appending the newline I advised?


  • @JonB said in How we can run Linux command from qt code?:

    QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
    if (f.open(QIODevice::WriteOnly))
    {
    qint64 count = f.write("24250000");
    Q_ASSERT(count > 0);
    f.close();
    }

    how I can pass variable instead of 24250000.



  • @JonB Thanks for your appreciated help!
    Your suggestion of QFile is working fine now.

    QFile f("/sys/bus/iio/devices/iio:device1/out_altvoltage1_TX_LO_frequency");
    if (f.open(QIODevice::WriteOnly))
    {
        qint64 count = f.write("2425000000");
        Q_ASSERT(count > 0);
        f.close();
    }
    

    The value 2425000000 is coming from a variable which can be change any time. I need to pass this value as a variable instead of constant 2425000000.
    thanks



  • @Wasee said in How we can run Linux command from qt code?:

    The value 2425000000 is coming from a variable which can be change any time. I need to pass this value as a variable instead of constant 2425000000.
    thanks

    Are you joking???
    Do you really don't have any idea how to do this simple stuff?
    It is so complicated to create a string and write it to a file?
    What did you try to do?



  • @Wasee
    You must convert your (integer) variable to a string. QIODevice::write() accepts either a const char * or a const QByteArray & for the string to write. You can use either QString::number() or QByteArray::number() to convert a number to a string/byte array to pass to write(), as you please.


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