When printing the "usage" of an application, should it be done on stdout or on stderr?
Depending on the application I've seen several cases, but there doesn't seem to be one rule. Maybe I'm mistaken and there is one good practice. In that case, what is it?
Never thought about it, but why not write the usage instructions to stderr if the program was called with no or wrong arguments, and write it to stdout when called with a --help (or similar) argument? This way, if the usage is shown because of an error, it goes to stderr, and if it's not an error because the user requested it, it goes to stdout. Seems logical, somehow.