reading and writing to QProcess in Qt Console Application - c++

Question

Noted: this appears to be a specific issue question but hopefully it can be edited for all to related to
I need to interact with a QProcess object.
The Problem:
I am not getting any output from QProcess after calling QProcess:write(input)
More Info:
Going through the doc pages led me to create an example below:
I have a script requesting user input, and finally displaying and appropriate message based on the user input.
Testing:
After adding a "log" feature to my script for testing, the following occurs:
script executes
script requests user input (confirmed by the 'first' qDebug() << p->readAll())
script accepts input from QProcess (confirmed by script 'log output')
After this, no output is received. The following 2 debug statements both fire (i.e. wait 30s each)
if (!p->waitForReadyRead()) {
qDebug() << "waitForReadyRead() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
if (!p->waitForFinished()) {
qDebug() << "waitForFinished() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
Followed by:
QString s = QString(p->readAll() + p->readAllStandardOutput());
where s is an empty string.
The issue is s should contain either "success" or "failed"
Calling Code:
QString cmd = QString("sh -c \"/path/to/bashscript.sh\"");
QString input = QString("Name");
QString result = runCommand(cmd, input)
Process Code:
//takes 2 parameters,
// cmd which is the code to be executed by the shell
// input which acts as the user input
QString runCommand(QString cmd, QString input){
QProcess *p = new QProcess(new QObject());
p->setProcessChannelMode(QProcess::MergedChannels); //no actual reason to do this
p->start(cmd);
if (p->waitForStarted()) {
if (!p->waitForReadyRead()) {
qDebug() << "waitForReadyRead() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
if (!p->waitForFinished()) {
//reads current stdout, this will show the input request from the bash script
//e.g. please enter your name:
qDebug() << p->readAll();
//here I write the input (the name) to the process, which is received by the script
p->write(ps.toLatin1());
//the script should then display a message i.e. ("success" o "failed")
if (!p->waitForReadyRead()) {
qDebug() << "waitForReadyRead() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
if (!p->waitForFinished()) {
qDebug() << "waitForFinished() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
}
QString s = QString(p->readAll() + p->readAllStandardOutput());
return s;
}
else{
qDebug() << "waitForStarted() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
p->waitForFinished();
p->kill();
return QString();
}
script.sh (-rwxrwxr-x)
#!/bin/bash
#returns
# "success" on non empty $n value
# "failed: on empty $n value
#
echo "enter your name:"
read n
if [[ ! -z $n ]];
then
echo "success"
exit 0;
else
echo "failed"
exit 1;
fi
UPDATE
#KevinKrammer I modified the run command as you said, also using the QStringList with the args.
Still does not get output, infact the waitForReadyRead() and waitForFinished() returns false instantly.
Called with:
QString r = runCommand(QString("text"));
Process Code:
QString runCommand(QString input){
QProcess *p = new QProcess(new QObject());
p->setProcessChannelMode(QProcess::MergedChannels);
//script is the same script refered to earlier, and the `cd /home/dev` IS required
p->start("sh", QStringList() << "-c" << "cd /home/dev" << "./script");
;
if (p->waitForStarted()) {
if (!p->waitForReadyRead(5000)) {
qDebug() << "waitForReadyRead() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
qDebug() << p->readAll();
p->write(input.toLatin1());
if(!p->waitForFinished(5000)){
qDebug() << "waitForFinished() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
QString s = QString(p->readAll() + p->readAllStandardOutput());
return s;
}
else{
qDebug() << "waitForStarted() [false] : CODE: " << QVariant(p->error()).toString() << " | ERROR STRING: " << p->errorString();
}
p->waitForFinished();
p->kill();
return QString();
}
Terminal Output of the Process:
started
readChannelFinished
exit code = "0"
waitForReadyRead() [false] : CODE: "5" | ERROR STRING: "Unknown error"
""
waitForFinished() [false] : CODE: "5" | ERROR STRING: "Unknown error"
Press <RETURN> to close this window...
Thoughts on this?
UPDATE 2
#Tarod Thank you for taking the time to make a solution.
It works, however not completely is expected.
I copied over your code, exactly.
Made a few changes in the mReadyReadStandardOutput()
See additional info below.
The problem:
After running the application (and script), I get a result -> AWESOME
Everytime it is the incorrect result i.e. "failed". -> NOT AWESOME
Terminal Output:
void MyProcess::myReadyRead()
void MyProcess::myReadyReadStandardOutput()
"enter your name:\n"
""
void MyProcess::myReadyRead()
void MyProcess::myReadyReadStandardOutput()
"failed\n"
Press <RETURN> to close this window...
script contents:
#!/bin/bash
echo "enter your name:"
read n
echo $n > "/tmp/log_test.txt"
if [[ ! -z "$n" ]];
then
echo "success"
exit 0;
else
echo "failed"
exit 1;
fi
/tmp/log_test.txt output
myname
running this manually from console:
dev#dev-W55xEU:~$ ls -la script
-rwxrwxr-x 1 dev dev 155 Jan 25 14:53 script*
dev#dev-W55xEU:~$ ./script
enter your name:
TEST_NAME
success
dev#dev-W55xEU:~$ cat /tmp/log_test.txt
TEST_NAME
Full code:
#include <QCoreApplication>
#include <QProcess>
#include <QDebug>
class MyProcess : public QProcess
{
Q_OBJECT
public:
MyProcess(QObject *parent = 0);
~MyProcess() {}
public slots:
void myReadyRead();
void myReadyReadStandardOutput();
};
MyProcess::MyProcess(QObject *parent)
{
connect(this,SIGNAL(readyRead()),
this,SLOT(myReadyRead()));
connect(this,SIGNAL(readyReadStandardOutput()),
this,SLOT(myReadyReadStandardOutput()));
}
void MyProcess::myReadyRead() {
qDebug() << Q_FUNC_INFO;
}
void MyProcess::myReadyReadStandardOutput() {
qDebug() << Q_FUNC_INFO;
// Note we need to add \n (it's like pressing enter key)
QString s = this->readAllStandardOutput();
qDebug() << s;
if (s.contains("enter your name")) {
this->write(QString("myname" + QString("\n")).toLatin1());
qDebug() << this->readAllStandardOutput();
}
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
MyProcess *myProcess = new MyProcess();
QString program = "/home/dev/script";
myProcess->start("/bin/sh", QStringList() << program);
a.exec();
}
#include "main.moc"
script issue? QProcess issue?

Answer 1

Unfortunately I don't have all your code, so I made an example. I hope it helps you.
If I compare my code to yours, I think the problem could be you are not calling readAllStandardOutput() after writing or maybe you are not calling exec() in your main.cpp.
#include <QCoreApplication>
#include <QProcess>
#include <QDebug>
class MyProcess : public QProcess
{
Q_OBJECT
public:
MyProcess(QObject *parent = 0);
~MyProcess() {}
public slots:
void myReadyRead();
void myReadyReadStandardOutput();
};
MyProcess::MyProcess(QObject *parent)
{
connect(this,SIGNAL(readyRead()),
this,SLOT(myReadyRead()));
connect(this,SIGNAL(readyReadStandardOutput()),
this,SLOT(myReadyReadStandardOutput()));
}
void MyProcess::myReadyRead() {
qDebug() << Q_FUNC_INFO;
}
void MyProcess::myReadyReadStandardOutput() {
qDebug() << Q_FUNC_INFO;
// Note we need to add \n (it's like pressing enter key)
this->write(QString("myname" + QString("\n")).toLatin1());
// Next line no required
// qDebug() << this->readAll();
qDebug() << this->readAllStandardOutput();
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
MyProcess *myProcess = new MyProcess();
QString program = "/home/fran/code/myscript.sh";
myProcess->start("/bin/sh", QStringList() << program);
a.exec();
}
#include "main.moc"
Script to test the application:
echo "enter your name:"
read n
if [ ! -z "$n" ];
then
echo "success"
exit 0;
else
echo "failed"
exit 1;
fi