Ruby switch between file and standard input

Question

How would you create a variable that could be read. It would read from a specific file if it exists, otherwise it would read from standard input. Sort of:

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

This does not work, but I think it needs to be done quite often, but I cannot find a good way to do this.

Answer 1

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

Answer 2

Does this work for you?

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

Answer 3

I think ruby ​​has the ability to process arguments that are not used before STDIN is first used as if they were file names for files connected to standard inputs.