repl

ruby -e "loop { print '>> '; puts('=> ' + eval(gets).inspect) }"

repl.rb

# A ruby REPL with optional readline support.
# Every ruby implementation that supports exception handling
# and eval should be able to run this.

def get_code(prefix)
  code = ""
  begin
    require "readline"
    code = Readline::readline prefix
    Readline::HISTORY.push code
  rescue Exception # maybe no readline support or some error
    print prefix
    code = gets
  end 
  code
end

REPL_BINDING = binding if defined? binding

loop do
  result = nil
  code = get_code ">> "
  begin
    if defined? REPL_BINDING
      result = eval code, REPL_BINDING
    else
      result = eval code
    end
  rescue Exception => e
    exit if e.is_a? SystemExit  
    puts(e.class.name + ": " e.to_s) # avoiding "#{..}"
  end
  begin
    puts("=> " + result.inspect)
  rescue NameError # maybe we don't support inspect
    puts("=> " + result.to_s)
  end
end

Small typo on line 31 with a missing +.