Question

I recently implemented a progress bar class in C++. I wrote something like

cout << "\r" << percentage_done << "%" << flush;

Now I am running some programs piping the output to less.
The problem is that less shows me a lot of lines of the type

^M1%^M2%…

So the “\r” is not interpreted correctly. Is it possible to pipe this in such a way
that less will only show the final 100% line or do I have to add a switch to my program
to disable the progression bars entirely?

I have the same problem when I pipe the output directly to a file, so the output files
occupy a lot of disk space unnecessarily.

Answer 1

Well, I think that it was quite right what Jan Hudec said. I wrote myself a small function

#include <unistd.h>

bool stdout_has_terminal()
{
  return NULL != ttyname(STDOUT_FILENO);
}

Depending on the return value I either print the progression bar or not. Now everything works quite nicely 🙂