How can I determine if my process is being run interactively?

Question

Is there a standard(ish) POSIX way of determining if my process (I’m writing this as a Ruby script right now; but I’m curious for multiple environments, including Node.js and ISO C command-line applications) is being run in an interactive terminal, as opposed to, say, cron, or execution from another tool, or… so on and so forth.

Specifically, I need to acquire user input in certain situations, and I need to fail fatally if that is determinably not possible (i.e. being run by cron.) I can do this with an environment variable, but I’d prefer something more standard-ish, if I can.

Answer 1

I've always used $stdout.isatty to check for this. Other approaches might include checking the value of ENV['TERM'] or utilizing the ruby-terminfo gem.

Answer 2

The closest you'll get, AFAIK, is isatty(). But as the page itself says, nothing guarantees that a human is controlling the terminal.