From: Daniel Martin <martin@...>
Date: 2006-08-07T10:39:49+09:00
Subject: Re: How to redirect a string to stdin within code?

Alex Young <alex@blackkettle.org> writes:

> But:
>
> alex@pandora:~$ irb
> irb(main):001:0> require 'stringio'
> => true
> irb(main):002:0> input = StringIO.new("myname")
> => #<StringIO:0xb7a42864>
> irb(main):003:0> $stdin = input
> => #<StringIO:0xb7a42864>
> /usr/lib/ruby/1.8/irb/input-method.rb:97: [BUG] Segmentation fault
> ruby 1.8.4 (2005-12-24) [i486-linux]
>
> Aborted
>
>
> This is on Ubuntu Breezy.  Any idea why that happens?

Well, that particular line of the irb source is calling the method
"readline" which is defined in readline.so - that is, in C.  My guess
is that it has some very specific assumptions about what type of
object it's reading from.  When I try that, I get:

esau:~$ irb
irb(main):001:0> require 'stringio'
=> true
irb(main):002:0> stream = StringIO.new("p [1,2,3,4]")
=> #<StringIO:0xb7c9c734>
irb(main):003:0> $stdin = stream
=> #<StringIO:0xb7c9c734>
/usr/lib/ruby/1.8/irb/input-method.rb:97:in `readline': wrong argument
type StringIO (expected File) (TypeError)
        from /usr/lib/ruby/1.8/irb/input-method.rb:97:in `gets'
        from /usr/lib/ruby/1.8/irb.rb:132:in `eval_input'
        from /usr/lib/ruby/1.8/irb.rb:259:in `signal_status'
        from /usr/lib/ruby/1.8/irb.rb:131:in `eval_input'
        (many more lines of stacktrace omitted)

This is on my Debian testing system, so I should be running the same
binary as you are, in theory:

esau:~$ ruby -v
ruby 1.8.4 (2005-12-24) [i486-linux]

Note that "irb --noreadline" won't have this problem, but that has
other issues (such as the fact that arrow keys don't work any more):

esau:~$ irb --noreadline
irb(main):001:0> require 'stringio'
=> true
irb(main):002:0> stream = StringIO.new("p [1,2,3,4]")
=> #<StringIO:0xb7cdb7b8>
irb(main):003:0> $stdin = stream
=> #<StringIO:0xb7cdb7b8>
irb(main):004:0> irb(main):004:0> [1, 2, 3, 4]
=> nil
irb(main):004:0> esau:~$