why QProcess not show output of ls /dev/sd* command ?

[Qt embedded developer]

i have implemted below code to find usb device name to print but its not working .

Actually this command working when execute on linux terminal.

 Command = "ls";

args<<" /dev/sd*"

    OProcess.start(Command,args,QIODevice::ReadOnly); //Starts execution of command
    OProcess.waitForFinished();                       //Waits for execution to complete

    QString sFromDateTime = OProcess.readAllStandardOutput();  //Reads standard output
    QString StdError = OProcess.readAllStandardError();

    if(StdError.isEmpty())
    {

        qDebug() << "output : " << sFromDateTime;

            QStringList List;
               List = sFromDateTime.split("\n");
               List = List.filter("/dev");
               foreach(QString item, List)
                      qDebug() << "List items = " << item;
    }
    else
    {
        qDebug() << "StdError:" << StdError;
    }

[JonB]

@Qt-embedded-developer
Because your /dev/sd* has a * wildcard in it. ls (or any other Linux command) does not expand wildcards. Only a shell expands wildcards! If you want to do it this way you will need:

 Command = "/bin/sh";

args << "-c" << "ls /dev/sd*";

Note that running a command to expand a filepath like this is not "efficient". You could do the work from, say, Qt QDir on /dev and look through the child filenames yourself to see which start with sd. Or QFileInfoList QDir::entryInfoList(const QStringList &nameFilters, QDir::Filters filters = NoFilter, QDir::SortFlags sort = NoSort) const could be used to do the wildcard matching. This would also be a lot cleaner than your code trying to parse ls's output.

[jsulm]

@Qt-embedded-developer said in why QProcess not show output of ls /dev/sd* command ?:

Command = "ls";

Use whole path to ls instead of relative path.
Also, always add error handling code (https://doc.qt.io/qt-6/qprocess.html#errorOccurred) to know what happens...
"/dev/sd*" will NOT work with QProcess, because the shell is resolving *.

[Qt embedded developer]

@jsulm said in why QProcess not show output of ls /dev/sd* command ?:

shell is resolving *

so what i need to do to execute it ?

i think its not relative path this is absolute path. if not then can you let me know how i can get absolute path ?

[JonB]

@Qt-embedded-developer
Because your /dev/sd* has a * wildcard in it. ls (or any other Linux command) does not expand wildcards. Only a shell expands wildcards! If you want to do it this way you will need:

 Command = "/bin/sh";

args << "-c" << "ls /dev/sd*";

Note that running a command to expand a filepath like this is not "efficient". You could do the work from, say, Qt QDir on /dev and look through the child filenames yourself to see which start with sd. Or QFileInfoList QDir::entryInfoList(const QStringList &nameFilters, QDir::Filters filters = NoFilter, QDir::SortFlags sort = NoSort) const could be used to do the wildcard matching. This would also be a lot cleaner than your code trying to parse ls's output.

[jsulm]

@Qt-embedded-developer said in why QProcess not show output of ls /dev/sd* command ?:

i think its not relative path this is absolute path

How is ls an absolute path?!
On my Ubuntu machine the absolute path to ls is /usr/bin/ls

I'm wondering why you need QProcess for such a task at all? You can simply use https://doc.qt.io/qt-6/qdir.html

[jsulm]

@Qt-embedded-developer said in why QProcess not show output of ls /dev/sd* command ?:

can you let me know how i can get absolute path ?

Execute the bellow command:
which ls

[JonB]

@jsulm said in why QProcess not show output of ls /dev/sd* command ?:

which ls

Observation: if which finds ls then there is no need to use a full path to it. And if it's not on your path which won't find it! :)

[Qt embedded developer]

@jsulm means i just need to check there is file name start with sd is there on not int /dev directory

[Qt embedded developer]

@JonB said in why QProcess not show output of ls /dev/sd* command ?:

QFileInfoList QDir::entryInfoList(const QStringList &nameFilters, QDir::Filters filters = NoFilter, QDir::SortFlags sort = NoSort) const

as per my case what i need to write in above ?

[jsulm]

@Qt-embedded-developer Yes, get entries in /dev folder using QDir::entryInfoList and filter all entries starting with sd (you can pass file name filter directly to QDir::entryInfoList).

[jsulm]

@Qt-embedded-developer said in why QProcess not show output of ls /dev/sd* command ?:

as per my case what i need to write in above ?

What exactly is not clear?

[Qt embedded developer]

@jsulm sorry its clear. i have to try. but if possible can you give example so it can help better.

[Christian Ehrlicher]

@Qt-embedded-developer said in why QProcess not show output of ls /dev/sd* command ?:

but if possible can you give example so it can help better.

Maybe reading the answers would help - it was already given...

[Qt embedded developer]

@Christian-Ehrlicher i have tried like below but i am getting empty list from fileinfolist

QString myPath="/dev";
        QDir dir;
        dir.setPath(myPath);
        QStringList filters;
        filters<<"sd";
        dir.setFilter( QDir::AllEntries | QDir::System);
        dir.setNameFilters(filters);
        dir.setSorting(QDir::Name );
        QFileInfoList list = dir.entryInfoList();

why my list is not giving file name what is expected ?

[Christian Ehrlicher]

Because there is no /dev/sd in your directory. Please read the documentation...

[Qt embedded developer]

@Christian-Ehrlicher actually above code i written to find name that start with sd .

[Christian Ehrlicher]

@Qt-embedded-developer said in why QProcess not show output of ls /dev/sd* command ?:

actually above code i written to find name that start with sd .

No, RTFM!

[JonB]

@Qt-embedded-developer said in why QProcess not show output of ls /dev/sd* command ?:

filters<<"sd";

void QDir::setNameFilters(const QStringList &nameFilters)

Each name filter is a wildcard (globbing) filter that understands * and ? wildcards. See QRegularExpression::fromWildcard().