qt run shell commands via qprocess

Question

I am developing a small QT application to interact with the terminal, to send commands to the terminal and to read back information printed out.

Example: get output of all processes using ps -aux

PROBLEM

I am able to write information out to the terminal but I dont think it is in the system scope, actual example:

Command passed to shell interpreter : "echo "pre"; ps -aux; echo "post"

edit from comment:

I need to send specific complete commands, I am not looking for shortened or alternative commands, I require a method of sending a command like this : ps -aux | grep chrome | tr -s " " | cut -d " " -f 2 and reading its output. This example is getting all pid's of all running chrome processes

Interpreters attempted :

• sh
• /bin/bash

Code:

QProcess *proc_ovpn = new QProcess(this);
proc_ovpn->waitForFinished();
proc_ovpn->start("sh",QStringList() << "-c" << "echo \"pre\";ps -aux; echo \"post\"");
proc_ovpn->setProcessChannelMode(QProcess::MergedChannels);
QString str(proc_ovpn->readAllStandardOutput());
return str;                             <<< ======= //breakpoint here

Debug information:

When breakpoint is reached, debug information as follows:

Locals      
    str ""  QString
    this    @0x555555ad7be0 Interface
Inspector       
Expressions     
Return Value        
Tooltip     
    10000000    10000000    int

It was suggested to run shell code using this method above from a post on SO, could not find it again.

I am at a loss, I do not understand why running these commands to not interact directly with the system (and its information),

Any advice?

Answer 1

you need to use waitForFinished() after start, not before

proc_ovpn->start("sh",QStringList() << "-c" << "echo \"pre\";ps -aux; echo \"post\"");
proc_ovpn->waitForFinished();

Note that waitForFinished() blocks until the process (that has been invoked by start) has finished ...

Also, you may check if the process is started successfully and/or if waitForFinished timed out

proc_ovpn->start("sh",QStringList() << "-c" << "echo \"pre\";ps -aux; echo \"post\"");

if(!proc_ovpn->waitForStarted()) //default wait time 30 sec
    qWarning() << " cannot start process ";

int waitTime = 60000 ; //60 sec
if (!proc_ovpn->waitForFinished(waitTime))
         qWarning() << "timeout .. ";