How to check ARGF is empty or not in Ruby

Question

I want to do with ARGF like this.

# file.rb
if ARGF.???
  puts ARGF.read
else
  puts "no redirect."
end

$ echo "Hello world" | ruby file.rb
Hello world

$ ruby file.rb
no redirect.

I need to do without waiting user input. I tried eof? or closed? doesn't help. Any ideas?

NOTE I was misunderstood ARGF. please see comments below.

Answer 1

Basically you'd examine #filename. One way to do this is:

if ARGF.filename != "-"
  puts ARGF.read
else
  puts "no redirect."
end

And this is the more complete form:

#!/usr/bin/env ruby
if ARGF.filename != "-" or (not STDIN.tty? and not STDIN.closed?)
  puts ARGF.read
else
  puts "No redirect."
end

Another:

#!/usr/bin/env ruby
if not STDIN.tty? and not STDIN.closed?
  puts STDIN.read
else
  puts "No redirect."
end

Answer 2

There might be a better way, but for me I needed to read the contents of a files being passed as arguments as well as having a files contents redirected to stdin.

my_executable

#!/usr/bin/env ruby
puts ARGF.pos.zero?

Then

$ my_executable file1.txt   # passed as argument
#=> true
$ my_executable < file1.txt # redirected to stdin
#=> true
$ my_executable
#=> false