isatty(3) is a common way to do this. However, it took typical CLIs a while to actually do something useful with it. Turning off colours is one thing you migh

isatty(3) is a common way to do this. However, it took typical CLIs a while to actually do something useful with it. Turning off colours is one thing you might want to do. For me, git with its automatic pager support has done the first really useful showcase of that.