I have been looking for the answer to this super simple problem and have tried many different approaches. All i want to do is run a linux bash command from inside of my Qt program with QProcess. This is my code: QProcess *proc = new QProcess(); proc->start("/bin/bash"); proc->waitForStarted(); qDebug() << proc->environment(); proc->write("echo 'reboot' > /dev/ttyS0\n"); qDebug() << proc->error() << ":" << proc->errorString(); when i try to trigger this command, i do not get the intended result and my error string looks like QProcess::ProcessError(UnknownError) : "Unknown error" Very frustrating, I would appreciate some guidance.

Hi, Because there was no error coming from bash. But since you want to write to a file, why not use QFile ? Or since you are using a serial port, why not QSerialPort ?

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Writing commands to linux bash

Solved General and Desktop

21 Posts 5 Posters 5.4k Views

J JonB
5 Jul 2018, 15:43
@devDawg said in Writing commands to linux bash:

@JonB Holy moly.. It worked. Why the extra "-c" argument? Is this to denote console?

That's why UNIX provides man bash :)

The simplest way to get any of the shells to execute a simple command is:
```
/bin/bash -c "the command as a single argument"
```
The -c says that a single argument follows of the entire command to be executed. Nothing to do with console.

Your original code did not pass that, and instead tried to run a bash without that argument, and present the command to be executed on the shell's stdin (same as -s argument). I am unsure why that did not in fact work, but using -c is preferable in any case.

It's good that this works now. But still a bit of overkill just to get a string sent to a device. I do think you should retry the "file" approach, but just use QFile (make sure you close it at the end) on /dev/ttyS0 instead of all that serial port code.
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devDawg

wrote on 5 Jul 2018, 16:02 last edited by

#21

@JonB You may think it is overkill, and you are probably right, but it accomplishes what I need. For the meantime, I will settle for this so I can focus on other tasks at hand.

I really appreciate your patience and willingness to help, thank you @JonB !
Anything worthwhile is never achieved easily.
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5 Jul 2018, 16:02