How to write to stderr so people will like you

"flush stdout, write your message to stderr, then flush stderr."<p>Standard Error is unbuffered: <a href="http://www.opengroup.org/onlinepubs/009695399/functions/stdin.html" rel="nofollow">http://www.opengroup.org/onlinepubs/009695399/functions/stdi...</a><p>"When opened, the standard error stream is not fully buffered; the standard input and standard output streams are fully buffered if and only if the stream can be determined not to refer to an interactive device."

If you can't recompile the program, an <i>expect</i> script will come very handy:<p><pre><code> $ ./unbuffer ./tst &#62;/tmp/logit 2&#62;&#38;1; cat /tmp/logit line 1 stderr line 1 line 2 stderr line 2 </code></pre> <a href="http://expect.nist.gov/example/unbuffer" rel="nofollow">http://expect.nist.gov/example/unbuffer</a>

This is a nice paradigm when it works, however for programs that are often piped to other programs, I believe this can run into issues with the flush on stdout blocking. Am I wrong here?

imho better way to solve this 'problem' would be to write error messages in such way that you don't need stdout as context to interpret them.

"(Note that programs that run other programs need to do more than just this; they need to flush stdout and perhaps stderr before they start another program.)"<p>Could someone explain exactly why this is?

a good practice is not to combine stdout and stderr into the same output when the ordering matters. You'll get a different result depending on the shell you are using.

Erm... if the problem is that stdout may be fully buffered, just set it to line buffered explicitly? (See setbuf(3) and friends.)<p>(Note that only stdout is the issue, see ready's comment.)

I'm in the habit of using doing a setbuf(stdout,NULL) in the beginning of all my console apps, anyway. Buffered console I/O is something that made sense 20 years ago but certainly not anymore.<p>If you did a setbuf(stderr,NULL) as well as setbuf(stdout,NULL), you'd achieve the same effect that the author's going for, with no need to remember to flush.