Qt – how to get output system() command in Qt

qprocessqtsystem

I use system() command in Qt. and I want to get output and show it to users.
my command is:

system("echo '" + rootPass.toAscii() + "' | su - root -c 'yum -y install " + packageName.toAscii() + "'");

this command can't run when I use it in QProcess (start or execute function)
but if i can run this command in QProcess i can get output with QProcess::readAllStandardOutput() function.

also when i used ">" in system command to save output in a file, I receive output when the package completely installed. like bellow:

system("echo '" + rootPass.toAscii() + "' | su - root -c 'yum -y install " + packageName.toAscii() + "' > result.out");

is there any idea about running this command with QProcess, or get output from system() command as soon as write each line.

Best Answer

You can also obtain the output directly from QProcess

QProcess process;
process.start(/* command line stuff */);
process.waitForFinished(-1); // will wait forever until finished

QString stdout = process.readAllStandardOutput();
QString stderr = process.readAllStandardError();

If you don't want to block your event loop, you can always use the signals:

readyReadStandardOutput();
readyReadStandardError();

And then call a function to readAllStandard[Output/Error]

Related Solutions

C++ – How to execute a command and get the output of the command within C++ using POSIX

#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>

std::string exec(const char* cmd) {
    std::array<char, 128> buffer;
    std::string result;
    std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd, "r"), pclose);
    if (!pipe) {
        throw std::runtime_error("popen() failed!");
    }
    while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {
        result += buffer.data();
    }
    return result;
}

Pre-C++11 version:

#include <iostream>
#include <stdexcept>
#include <stdio.h>
#include <string>

std::string exec(const char* cmd) {
    char buffer[128];
    std::string result = "";
    FILE* pipe = popen(cmd, "r");
    if (!pipe) throw std::runtime_error("popen() failed!");
    try {
        while (fgets(buffer, sizeof buffer, pipe) != NULL) {
            result += buffer;
        }
    } catch (...) {
        pclose(pipe);
        throw;
    }
    pclose(pipe);
    return result;
}

Replace popen and pclose with _popen and _pclose for Windows.

Ruby – Getting output of system() calls in Ruby

I'd like to expand & clarify chaos's answer a bit.

If you surround your command with backticks, then you don't need to (explicitly) call system() at all. The backticks execute the command and return the output as a string. You can then assign the value to a variable like so:

output = `ls`
p output

printf output # escapes newline chars

Best Answer

Related Solutions

C++ – How to execute a command and get the output of the command within C++ using POSIX

Ruby – Getting output of system() calls in Ruby

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