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Ruby Programming
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Interactive Ruby

The easiest way to run Ruby interactively is simply to type ``ruby'' at the shell prompt.

% ruby
puts "Hello, world!"
Hello, world!

Here we typed in the single puts expression and an end of file character (which is control-D on our system). This process works, but it's sort of painful if you make a typo, and you can't really see what's going on as you type.

In the sample directory in the Ruby distribution you'll find a script named ``eval.rb''. It goes one step better by showing us the value of each expression as it is entered:

% cd sample
% ruby eval.rb
ruby> a = "Hello, world!"
"Hello, world!"
ruby> puts a
Hello, world!
ruby> ^D

Here we can see the output from puts, and then the return value from puts (which is nil).

That's all fine and well, except that multiline expressions do not work, and you can't edit the line you're on, or go back and use previous lines (as you might with command history in a shell).

For the next step up from eval.rb, we have irb---Interactive Ruby. irb is a Ruby Shell, complete with command-line history, line editing capabilities, and job control. It is quite configurable and has many options, so much so that it has its own appendix beginning on page 517. We recommend that you get familiar with irb so you can try some of our examples interactively.
Ruby Programming
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