test -t 1 to Check for Terminal Outputtest -t will check if the stream represented by the number is a
terminal (tty). By testing standard output you know that your code is
being piped to something else (not a terminal) if it is not true.
By the way, this is entirely different than figuring out if your code is running in an “interactive” session with a user (which is usually not really want to want, and it problematic to determine because it is at least slightly different for every shell enough to make it inconsistent to write compatible code).