Suppose that you're writing a command like, say, make ; it writesprogress output to standard output and error reports to standard error,and it doesn't necessarily immediately terminate when it encounters anerror (or prints a warning; the important thing is that it keeps runningafter it prints things to standard error).

There's a subtle catch in how you want to print things (such as standard error messages ) to stderrin such a program. You don't want to just do the