Question

This question maybe not related to Emacs only, but to all development environment that use Console for its debugging process. Here is the problem. I use Eshell to run the application we are being developed. It’s a J2ME application. And for debugging, we just use System.out.println(). And now, suppose I want to allow only text that started with Eko: to be displayed in the console (interactively), is it possible?

I installed Cygwin in my Windows environment, and try to grep the output like this :
run | grep Eko:. It surely filtered only output with Eko: as the beginning, but it’s not interactive. The output suppressed until the application quit. Well, that’s useless anyway.

Is it possible to do it? What I mean is, we don’t have to touch the application code itself?

I tag to linux also, because maybe some guys in Linux know the answer.

Many thanks!

Answer 1

The short: Try adding --line-buffered to your grep command.

The long: I assume that your application is flushing its output stream with every System.out.println(), and that grep has the lines available to read immediately, but is choosing to buffer output until it has ‘enough’ output saved up to make writing make sense. (This is typically 4k or 8k of data, which could be several hundred lines, depending upon your line length.)

This buffering makes great sense when the output is another program in the pipeline; reducing needless context switches is a great way to improve program throughput.

But if your printing is slow enough that it doesn’t fill the buffer quickly enough for ‘real time’ output, then switching to line-buffered output might fix it.