Crash IRB (interactive Ruby)

Question

Ruby comes with a built-in REPL, which is quite handy.

Your challenge is to crash it in the least amount of code!

The definition of "crash" is "make it exit in an unintended way." This means exit, quit, abort, irb_exit, irb_quit, et. al. are not valid answers.

Furthermore, you may not cause any side-effect to any other part of the system. For example, `rm -rf /` is not valid either.

Any version 1.9.3 or above is valid. If your code only works on a specific version of Ruby, you may specify that in the answer.

The final restriction is that you may not rely on any gems.

This is code-golf, so the shortest code that crashes IRB will win!

Answer 1

5 characters

ENV=0

(inspired by @daniero's answer)

Answer 2

16 characters

String=0
String=0

Not the shortest, but I think it's funny that it doesn't crash until the second line. Generates roughly 20 lines of text before IRB exits. For some reason it cannot be shortened to for instance 2.times{String=0}.

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edit

Of all the answers so far, this is the only one that has worked for me (and it works in all versions I could get my hands on), and I've tested all of them in these versions:

On whatever kind of Linux I get when ssh'ing into my university:

ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-linux]
ruby 1.8.5 (2006-08-25) [x86_64-linux]

Mac OS X Mavericks default:

ruby 2.0.0p247 (2013-06-27 revision 41674) [universal.x86_64-darwin13]

Installed through Homebrew on OS X:

ruby 1.9.3p448 (2013-06-27 revision 41675) [x86_64-darwin12.4.0]

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edit 2

7 characters

Combining my first version (and/or @Howard's answer, for maximum cross reference) with @chinese perl goth's answer:

STDIN=0

Answer 3

12 chars

ruby is not exactly my cup of tea, but I've just found out that irb acts funny when I close the stdin :)

$stdin.close

tested on irb 0.9.6(09/06/30) and ruby 1.9.3p194

Answer 4

10 9 chars

A shorter variant on @daniero's answer:

String=1
-

This works at least in the default OS X Mavericks Ruby (2.0.0).

The answer basically relies on the fact that the Ruby Token function does a case on the input token. One of the cases checks against String, which has been redefined by the first line. This case fails, so the case falls through to the default, which assumes the object has an ancestors accessor (which it does not).

Because the "bug" is in the tokenizer, the first line won't fail because the line only takes effect after the parsing is finished. Thus, it only affects subsequent lines. Subsequent lines must contain some kind of operator in order to see the failure.

Answer 5

5 characters

$>=$<

Sets stdout to stdin which throws an error trying to open stdin for writing and crashes irb.

Answer 6

22 characters

def method_missing;end

Apparently it messes with some irb internals. (To fix it, add self. after def.)

Answer 7

12 characters

def send;end

As far as I know, there are four methods in the Object class which show this kind of behaviour:

send
method_missing
respond_to?
respond_to_missing?

Answer 8

5 Characters

IRB=0

Nothing disturbs IRB quite like redefining IRB.

Answer 9

12 10 characters

exec"exec"

I don't know if this counts, because of the exec

Answer 10

8 characters

Similar to chinese perl goth's answer:

$>.close

$> is an alias for STDOUT.

Answer 11

26 + 1 = 27 characters

This isn't very golfy, but I was amused to discover it by accident and thought others might enjoy it.

class Fixnum;def +;end end

I added +1 to the score because you have to press Enter a second time after entering the above (but not +2 because no one else counted Enter).