Command working in terminal, but not via QProcess

Question

ifconfig | grep \'inet\'

is working when executed via terminal. But not via QProcess

My sample code is

QProcess p1;
p1.star         


        

Answer 1

QProcess executes one single process. What you are trying to do is executing a shell command, not a process. The piping of commands is a feature of your shell.

There are three possible solutions:

Put the command you want to be executed as an argument to sh after -c ("command"):

QProcess sh;
sh.start("sh", QStringList() << "-c" << "ifconfig | grep inet");

sh.waitForFinished();
QByteArray output = sh.readAll();
sh.close();

Or you could write the commands as the standard input to sh:

QProcess sh;
sh.start("sh");

sh.write("ifconfig | grep inet");
sh.closeWriteChannel();

sh.waitForFinished();
QByteArray output = sh.readAll();
sh.close();

Another approach which avoids sh, is to launch two QProcesses and do the piping in your code:

QProcess ifconfig;
QProcess grep;

ifconfig.setStandardOutputProcess(&grep); // "simulates" ifconfig | grep

ifconfig.start("ifconfig");
grep.start("grep", QStringList() << "inet"); // pass arguments using QStringList

grep.waitForFinished(); // grep finishes after ifconfig does
QByteArray output = grep.readAll(); // now the output is found in the 2nd process
ifconfig.close();
grep.close();