[Solved] QProcess and backlight linux command

Memphis

Hello Guys!
I try to modify the brightness of my display in Qt, running the command:

echo 6 > /sys/class/backlight/mxs-bl/brightness

and using QProcess like this:

@QProcess *sh = new QProcess();
sh->start( "echo 6 > /sys/class/backlight/mxs-bl/brightness");
sh->waitForFinished();
QByteArray output = sh->readAll();
ui->label->setText(output);
sh->close();@

But it print only "6 > /sys/class/backlight/mxs-bl/brightness" instead of do the command like in the shell, and don't change the value of the brightness.
Any idea? Thank you so much.

raven-worx

try this:
@
QProcess *sh = new QProcess();
sh->write("6"); //write to stdin of the process
//sh->closeWriteChannel(); //not sure if this line is needed
sh->start( "/sys/class/backlight/mxs-bl/brightness");
@

Memphis

It didn't work, :-( don't change anything

raven-worx

ok... one more try:
@
QProcess *sh = new QProcess();
sh->start( "/sys/class/backlight/mxs-bl/brightness");
sh->write("6"); //write to stdin of the process
sh->closeWriteChannel();
@

Memphis

nothing to do, still does not do anything, but excuse me I should not include the echo command? is not recognized ">" sign on Qt

tomma

Why are you trying to use QProcess to write to file?
Wouldn't it be easier to use QFile?

@
QFile f("/sys/class/backlight/mxs-bl/brightness");
f.open(QIODevice::WriteOnly | QIODevice::Truncate);
f.write("6");
@

Memphis

Thank you it works ;-)

raven-worx

well ... i thought "/sys/class/backlight/mxs-bl/brightness" is a application rather than a file.
I thought you know what your were doing when you using QProcess in the first place ;)