Testing Whether a Program Is Running Interactively

Problem

You want to see whether theres another person on the other end of your program, or whether the program has been hooked up to a file or the output of another program.

Solution

STDIN.tty? returns true if theres a terminal hooked up to your programs original standard input. Since only humans use terminals, this will suffice. This code works on Unix and Windows:

#!/usr/bin/ruby -w # interactive_or_not.rb if STDIN.tty? puts "Let me be the first to welcome my human overlords." else puts "How goes the revolution, brother software?" end

Running this program in different ways gives different results:

$ ./interactive_or_not.rb Let me be the first to welcome my human overlords. $ echo "Some data" | interactive_or_not.rb How goes the revolution, brother software? $ ./interactive_or_not.rb < input_file How goes the revolution, brother software?

Discussion

An interactive application can be more user friendly than one that runs solely off its command-line arguments and input streams. By checking STDIN.tty? you can make your program have an interactive and a noninteractive mode. The noninteractive mode can be chained together with other programs or used in shell scripts.