Question

I’m trying to pass a byte array from inside my rails app into another ruby script (still inside my rails app), for example:

`./app/animations/fade.sh "\x01\x01\x04\x00" &`

Yields ArgumentError (string contains null byte)

I suppose I’m stumped with how I can form this string and than pass it to my script, which will use it in this sort of fashion:

@sp.write ["#{ARGV[0]}", "f", "\x12"]

I’d like to form the string (on my rails app) like this if possible:

led = "\x01#{led.id}\x04\x00"

But I keep getting ArgumentError (string contains null byte) error. Is there a way I can form this string from elements in my rails app, then pass it to my external script?

Answer 1

You should just pass the data in through standard input, not the command line. You can use IO.popen for this purpose:

IO.popen("./app/animations/fade.sh", "w+") do |f| 
  f.write "\x01\x01\x04\x00"
end

And on the reading side:

input = $stdin.read
@sp.write [input, "f", "\x12"]

(By the way, it’s more common to name Ruby scripts .rb instead of .sh; if fade.sh is meant to be a Ruby script, as I assume from the syntax you used in its example contents, you might want to name it fade.rb)