Question

Having looked at this question, I have the following code:

$/ = "\0"
answer = STDIN.gets

Now, I was hoping that this would allow the user to:

• enter a multi-line input, terminating by pressing Ctrl-D.
• enter a single line input, terminating by pressing Ctrl-D.
• enter a “nothing” input, terminating by pressing Ctrl-D.

However, the behaviour I actually see is that:

• The user can enter a multi-line input fine.
• The user can not enter a single line input, unless they hit Ctrl-D twice.
• The user can enter a “nothing” input if they hit Ctrl-D straight away.

So, why does the single line situation (i.e. if the user has entered some text but no newline and then hit Ctrl-D) require two presses of Ctrl-D? And why does it work then if the user enters nothing? (I have noted that if they enter nothing and hit Ctrl-D, I don’t get an empty string but the nil class – I discovered this when trying to call .empty? on the result, since it suddenly failed horribly. If there is a way to get it to return an empty string as well, that would be nice. I prefer checking .empty? to ==, and don’t particularly want to define .empty? for the nil class.)

EDIT: Since I really would like to know the “correct way” to do this in Ruby, I am offering a bounty of 200 rep. I will also accept answers that give another way of entering terminal multi-line input with a sensible “submit” procedure – I will be the judge of ‘suitable’. For example, we’re currently using two “\n”s, but that’s not suitable, as it blocks paragraphs and is unintuitive.

Answer 1

The basic problem is the terminal itself. See many of the related links to the right of your post. To get around this you need to put the terminal in a raw state. The following worked for me on a Solaris machine:

#!/usr/bin/env ruby
# store the old stty settings
old_stty = `stty -g`
# Set up the terminal in non-canonical mode input processing
# This causes the terminal to process one character at a time
system "stty -icanon min 1 time 0 -isig"
answer = ""
while true
  char = STDIN.getc
  break if char == ?\C-d # break on Ctrl-d
  answer += char.chr
end
system "stty #{old_stty}" # restore stty settings
answer

I’m not sure if the storing and restoring of the stty settings is necessary but I’ve seen other people do it.