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How we can run Linux command from qt code?

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  • WaseeW Wasee

    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!

    jsulmJ Offline
    jsulmJ Offline
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #2

    @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.

    1 Reply Last reply
    3
    • WaseeW Offline
      WaseeW Offline
      Wasee
      wrote on last edited by
      #3

      @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.

      jsulmJ 1 Reply Last reply
      0
      • WaseeW Wasee

        @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.

        jsulmJ Offline
        jsulmJ Offline
        jsulm
        Lifetime Qt Champion
        wrote on last edited by
        #4

        @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?!

        1 Reply Last reply
        2
        • WaseeW Offline
          WaseeW Offline
          Wasee
          wrote on last edited by
          #5

          @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

          jsulmJ 1 Reply Last reply
          0
          • WaseeW Wasee

            @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

            jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by
            #6

            @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...

            1 Reply Last reply
            0
            • WaseeW Offline
              WaseeW Offline
              Wasee
              wrote on last edited by
              #7

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

              jsulmJ JonBJ 2 Replies Last reply
              0
              • WaseeW Wasee

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

                jsulmJ Offline
                jsulmJ Offline
                jsulm
                Lifetime Qt Champion
                wrote on last edited by
                #8

                @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...

                1 Reply Last reply
                4
                • WaseeW Wasee

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

                  JonBJ Online
                  JonBJ Online
                  JonB
                  wrote on last edited by JonB
                  #9

                  @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();
                  }
                  
                  WaseeW 2 Replies Last reply
                  5
                  • JonBJ JonB

                    @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();
                    }
                    
                    WaseeW Offline
                    WaseeW Offline
                    Wasee
                    wrote on last edited by
                    #10

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

                    jsulmJ JonBJ 3 Replies Last reply
                    0
                    • WaseeW Wasee

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

                      jsulmJ Offline
                      jsulmJ Offline
                      jsulm
                      Lifetime Qt Champion
                      wrote on last edited by
                      #11

                      @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?

                      1 Reply Last reply
                      1
                      • WaseeW Wasee

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

                        jsulmJ Offline
                        jsulmJ Offline
                        jsulm
                        Lifetime Qt Champion
                        wrote on last edited by
                        #12
                        This post is deleted!
                        1 Reply Last reply
                        0
                        • WaseeW Wasee

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

                          JonBJ Online
                          JonBJ Online
                          JonB
                          wrote on last edited by JonB
                          #13

                          @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.

                          1 Reply Last reply
                          2
                          • WaseeW Offline
                            WaseeW Offline
                            Wasee
                            wrote on last edited by
                            #14

                            @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.

                            jsulmJ 1 Reply Last reply
                            0
                            • WaseeW Wasee

                              @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.

                              jsulmJ Offline
                              jsulmJ Offline
                              jsulm
                              Lifetime Qt Champion
                              wrote on last edited by
                              #15

                              @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.

                              WaseeW 1 Reply Last reply
                              0
                              • jsulmJ jsulm

                                @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.

                                WaseeW Offline
                                WaseeW Offline
                                Wasee
                                wrote on last edited by
                                #16

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

                                JonBJ 1 Reply Last reply
                                0
                                • WaseeW Wasee

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

                                  JonBJ Online
                                  JonBJ Online
                                  JonB
                                  wrote on last edited by
                                  #17

                                  @Wasee

                                  • Did you add the error checking code I advised?
                                  • Did you try appending the newline I advised?
                                  1 Reply Last reply
                                  0
                                  • JonBJ JonB

                                    @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();
                                    }
                                    
                                    WaseeW Offline
                                    WaseeW Offline
                                    Wasee
                                    wrote on last edited by
                                    #18

                                    @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.

                                    1 Reply Last reply
                                    0
                                    • WaseeW Offline
                                      WaseeW Offline
                                      Wasee
                                      wrote on last edited by
                                      #19

                                      @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

                                      KroMignonK JonBJ 2 Replies Last reply
                                      0
                                      • WaseeW Wasee

                                        @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

                                        KroMignonK Offline
                                        KroMignonK Offline
                                        KroMignon
                                        wrote on last edited by
                                        #20

                                        @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?

                                        It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                                        1 Reply Last reply
                                        0
                                        • WaseeW Wasee

                                          @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

                                          JonBJ Online
                                          JonBJ Online
                                          JonB
                                          wrote on last edited by
                                          #21

                                          @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.

                                          1 Reply Last reply
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