IRB

Remarks

Run the program with

ruby entry.rb

which will fire up an interactive Ruby shell (IRB). When you are done Rubying, you can exit it with EOF or exit!

Implementations

• Requires Ruby 2.5. Tested on ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux].

Features

• The IRB supports multiline input, including =begin..=end comments and heredocs
• Just paste the IRB anywhere to have to start it with the current binding (like binding.irb)
  • Tip: One way to test variable definitions below the IRB is by wrapping them within a BEGIN {} block
• Errors in the IRB will be printed directly
• No libraries and no single quotes are used, so you can directly pass it to ruby -e '…' on the command-line
• Unformatted, it fits into a tweet (which is currently defined to be <= 280 characters). After removing terminal color, it even fits into an old-style-140-chars tweet.

Limitation

• The multiline support is not perfect (on the other hand, neither is standard library's),
• The program uses/leaks the following local variables: _ (the multiline buffer) and __ (the binding)
• Kernel#exit does not work, because SystemErrors get caught
• No convenience features like history, readline, profile files, …

Internals

• The multiline mechansim works by catching errors and filtering the ones that complain about incomplete code. Simple, but efficient!
• Uses the eval + %w[] + nospaces + join technique for fancy formatting
• The following codegolf practices were used:
  • Dirty interpolation ("#$!")
  • $><< instead of print
  • "%p"%object instead of object.inspect
  • string<$/ instead of string!=""