Reading into the output of a long running shellExecute

[helxi]

Hi. I have not done any multi-threaded programming before. What I 
basically want is to read into the output of a long shellExecute 
function each second.

In details, I am calling shellExecute("pkexec dd if=/path/to/file 
of=/dev/sdx status=progress && sync");
It's a long running process and dd command prints how many bytes 
it has written in stdout continuously. I want to read and parse 
this output each second. How should I proceed?