How to Execute SCP command to transfer files to a target machine

[moyin]

@jsulm i tried this, it does't works.

    connect(&proc, SIGNAL(readyReadStandardError()), this, SLOT(readOutput()));
    connect(&proc, SIGNAL(readyReadStandardOutput()), this, SLOT(readOutput()));
    connect(&proc, SIGNAL(errorOccurred()), this, SLOT(readOutput()));
    proc.startDetached(command,params) ;

And did changes in readoutput() also,

    ui->textEdit_Standard_output->setText(ui->textEdit_Standard_output->toPlainText() + StdOut + StdError);

[moyin]

@jsulm @sierdzio i'm sharing my .h and .cpp files as well it may help u to understand my problem.

transfer.h

#ifndef TRANSFER_H
#define TRANSFER_H

#include <QDialog>
#include <QProcess>

namespace Ui {
class Transfer;
}

class Transfer : public QDialog
{
    Q_OBJECT

public:
    explicit Transfer(QWidget *parent = 0);
    ~Transfer();

private slots:
    void on_pushButton_Go_clicked();

    void on_pushButton_choosefile_transferTotarget_clicked();

    void on_pushButton_Std_output_clear_clicked();

    void on_checkBox_Show_Password_clicked(bool checked);

    void readOutput() ;

private:
    Ui::Transfer *ui;
    QProcess proc ;
/*
signals:
    void readyReadStandardOutput() ;
    void readyReadStandardError() ;
*/
};

#endif // TRANSFER_H

transfer.cpp

#include "transfer.h"
#include "ui_transfer.h"
#include <sstream>
#include <QProcess>
#include <iostream>
#include <QDebug>
#include <QFileDialog>
#include <QtWidgets>


Transfer::Transfer(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Transfer)
{
    ui->setupUi(this);
}

Transfer::~Transfer()
{
    delete ui;
}


void Transfer::on_pushButton_Go_clicked()
{
    //proc = new QProcess() ;
    QString command = "scp" ;
    QString ip = ui->lineEdit_IP_Address->text() ;
    QString username = ui->lineEdit_SSH_username->text() ;
    QString dest_path = ui->lineEdit_TransferToTarget_DestinationFolder->text() ;
    QString source_path = ui->lineEdit_TransferToTarget_SourcePath->text() ;
    std::stringstream s ;
    s << username.toStdString() << "@" << ip.toStdString() << ":" << dest_path.toStdString();
    std::cout << s.str() << std::endl ;
    QStringList params ;
    params.append(source_path) ;
    params.append(QString::fromStdString(s.str())) ;
    qDebug() << params ;
    //    params.append("/home/span51/Desktop/readme.txt");
    //    params.append("spanidea@192.168.1.26:/home/spanidea/test" );
    connect(&proc, SIGNAL(readyReadStandardError()), this, SLOT(readOutput()));
    connect(&proc, SIGNAL(readyReadStandardOutput()), this, SLOT(readOutput()));
    connect(&proc, SIGNAL(errorOccurred()), this, SLOT(readOutput()));
    proc.startDetached(command,params) ;

/*    QString StdOut      =   proc.readAllStandardOutput();  //Reads standard output
    QString StdError    =   proc.readAllStandardError();   //Reads standard error
    std::cout<<"\n Printing the standard output..........\n";
    std::cout<<endl<<StdOut.toStdString();
    std::cout<<"\n Printing the standard error..........\n";
    std::cout<<endl<<StdError.toStdString();
*/
}

void Transfer::on_pushButton_choosefile_transferTotarget_clicked()
{
    QString filepath = QFileDialog::getOpenFileName(this, tr("Transfer file"), "/home","Config_Files(*.c)") ;
    ui->lineEdit_TransferToTarget_SourcePath->setText(filepath);
}

void Transfer::on_pushButton_Std_output_clear_clicked()
{
    ui->textEdit_Standard_output->clear() ;
}

void Transfer::on_checkBox_Show_Password_clicked(bool checked)
{
    if (checked)
        ui->lineEdit_SSH_password->setEchoMode(QLineEdit::Normal);
    else
        ui->lineEdit_SSH_password->setEchoMode(QLineEdit::Password);
}

void Transfer::readOutput()
{
    QString StdOut = proc.readAllStandardOutput();  //Reads standard output
    QString StdError = proc.readAllStandardError(); // Reads standard error

//    ui->textEdit_Standard_output->setText(StdOut);
//    ui->textEdit_Standard_output->setText(StdError);
    ui->textEdit_Standard_output->setText(ui->textEdit_Standard_output->toPlainText() + StdOut + StdError);
}

[jsulm]

@moyin You again did not read documentation, right? http://doc.qt.io/qt-5/qprocess.html#errorOccurred
Else you would see that errorOccurred() has a parameter.
This connect cannot succeed (you should see a warning at runtime):

connect(&proc, SIGNAL(errorOccurred()), this, SLOT(readOutput()));

You need to use another slot with QProcess::ProcessError error parameter and print out its value.

[moyin]

@jsulm i can transfer file successfully to the target machine without errors. but wanted to redirect logs whatever (stdout,stderr, etc..,) to textedit. than
why should go for QProcess::ProcessError.

[jsulm]

@moyin Then check whether these connects actually were successful:

qDebug() << connect(&proc, SIGNAL(readyReadStandardError()), this, SLOT(readOutput()));
qDebug() << connect(&proc, SIGNAL(readyReadStandardOutput()), this, SLOT(readOutput()));

Place a qDebug() in your readOutput() to print something out to see whether the slot is actually called.

[moyin]

@jsulm i mentioned u already that, while debug if i put break point at or in readoutput() that will stop at break point so it means slot is not getting called.

[jsulm]

@moyin said in How to Execute SCP command to transfer files to a target machine:

while debug if i put break point at or in readoutput() that will stop at break point so it means slot is not getting called

sorry, I'm confused: if it stops at the break point inside readOutput() then it means that it is actually called.

Try this:

void Transfer::readOutput()
{
    QString StdOut = proc.readAllStandardOutput();  //Reads standard output
    QString StdError = proc.readAllStandardError(); // Reads standard error
    qDebug() << StdOut;
    qDebug() << StdError;
//    ui->textEdit_Standard_output->setText(StdOut);
//    ui->textEdit_Standard_output->setText(StdError);
    ui->textEdit_Standard_output->setText(ui->textEdit_Standard_output->toPlainText() + StdOut + StdError);
}

Do you see anything in Application Output?

[moyin]

@moyin said in How to Execute SCP command to transfer files to a target machine:

that will stop

sorry correction "that will not stop at breakpoint"

[sierdzio]

@moyin said in How to Execute SCP command to transfer files to a target machine:

proc.startDetached(command,params) ;

Hm, startDetached() is a static call, so attaching any signals to it won't work, right? Shouldn't start() be used here instead? Just a thought, I have not analysed this code in-depth.

[moyin]

@jsulm its printing true for both

qDebug() << connect(&proc, SIGNAL(readyReadStandardError()), this, SLOT(readOutput()));
qDebug() << connect(&proc, SIGNAL(readyReadStandardOutput()), this, SLOT(readOutput()));```

qDebug() in readOutput() is not printing any thing.

[jsulm]

@moyin This is your problem:

proc.startDetached(command,params) ;

startDetached() is a static method! So you start your process, but it is not managed by the proc instance! Use start() instead:

proc.start(command, params);

[moyin]

@jsulm i tried that also but failed.

[jsulm]

@moyin In what way failed? Same issue? Slot still not called?

[moyin]

@jsulm sorry, failed in the sense not able to print the logs into textEdit.

[moyin]

@jsulm yes slot is not getting called itself.

[moyin]

@jsulm
Slot still not called? Yes still not called.

[jsulm]

@moyin Can you post your current code?

[JonB]

@moyin
I'm lost as to where you're at.

But at least at one point you were told to use QProcess::startDetached() rather than QProcess:start(). I believe (untested by me, as usual, could be putting my neck on the line...) that you cannot properly redirect process input/output and/or get signals for input/output if you run the child process detached...?

[jsulm]

@JNBarchan This was already mentioned, but @moyin says that it isn't working even after changing to start().
There most be still something in the code, that's why I asked for the current code.

[JonB]

@jsulm
OK, as long he is not trying startDetached that's good...

FWIW, I happen to just be working on my own Dialog which spawns a sub-process (QProcess::start()), gets its output via signals, and copies it into scrolling text widget, and it's all working fine for me. As one would expect!

Purely BTW, given the command is an scp whose job is to copy the files, I wonder just what stdout/stderr output he is expecting? Has he informed us whether it's just the output that's missing/empty, or whether the whole command is not running in any case??