Ruby Switch Between File and Standard Input

Question

How would you create a variable that could be read. It would read from a certain file if it exists, otherwise it would read from standard input. Something like:

input = File.open("file.txt") || in

This doesn't work, but I think this should be done pretty often, but I can't find a nice way to do it.

Answer 1

This this works for you?

input = File.exist?("file.txt") ? File.open("file.txt") : STDIN

Answer 2

I think ruby has the ability to treat arguments that aren't used before STDIN is first used as if it were filenames for files piped into standard input.

Answer 3

See: ...run against stdin if no arg; otherwise input file =ARGV