Ruby Switch Between File and Standard Input

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 pret开发者_如何转开发ty often, but I can't find a nice way to do it.

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This this works for you?

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

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

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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.