In The output of Linux pipes can be indeterministic (via), Marek Gibney noticed that the following shell command has indeterminate output: (echo red; echo green 1>&2) | echo blue This can output any of "blue green" (with a newline between them), "green blue", or "blue"; the usual case is "blue green". Fully explaining this requires surprisingly arcane Unix knowledge. The "blue green" and "green bl