Question

I have some problem to figure out how I can maintain the pipe and redirect functionality of a shell once I find out that there are missing command line arguments.

If I for example use a scanf call, that will work with a re-direct or a pipe from a shell, but in absence of this I get a prompt, which I don’t want.

I would like to accept command line arguments through argv[], a pipe or re-direct but I can’t figure out how to do it with out getting the prompt. If I for example try something like this:

if(argc < 2)
    exit(0);

Then the program will terminate if I try this:

echo arg | myProgram

Or this:

myProgram < fileWithArgument

I have tried to look this up but I always get some bash scripting reference.

Answer 1

The common way to handle situations like this is to check if the standard input stream is connected to a terminal or not, using isatty or similar functions depending on your OS. If it is, you take parameters from the command line, if not (it’s been redirected), you read standard input.