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# Interactive Ruby (irb)

Interactive Ruby or irb is an interactive programming environment that comes with Ruby. It was written by Keiju Ishitsuka.

## Usage Syntax:

To invoke it, type irb at a shell or command prompt, and begin entering Ruby statements and expressions. Use exit or quit to exit irb.

    $ irb[.rb] [options] [programfile] [arguments]

Here is a complete list of options:

SN | Command with Description
--- | ---
1 | -f Suppress reading of the file ~/.irbrc.
2 | -m bc mode (load mathn library so fractions or matrix are available).
3 | -d Set $DEBUG to true (same as ruby -d).
4 | -r load-module Same as ruby -r.
5 | -I path Specify $LOAD_PATH directory.
6 | --inspect Use inspect for output (default except for bc mode).
7 | --noinspect Don't use inspect for output.
8 | --readline Use Readline extension module.
9 | --noreadline Don't use Readline extension module.
10 | --prompt prompt-mode (--prompt-mode prompt-mode) Switch prompt mode. Predefined prompt modes are default, simple, xmp, and inf-ruby.
11 | --inf-ruby-mode Use prompt appropriate for inf-ruby-mode on Emacs. Suppresses --readline.
12 | --simple-prompt Simple prompt mode.
13 | --noprompt No prompt mode.
14 | --tracer Display trace for each execution of commands.
15 | --back-trace-limit n Display backtrace top n and tail n. The default value is 16.
16 | --irb_debug n Set internal debug level to n (not for popular use).
17 | -v (--version). Print the version of irb.

## Example:

Here is a sample of irb evaluating a variety of expressions::

    $ irb
    irb(main):001:0> 23 + 27
    => 50
    irb(main):002:0> 50 - 23
    => 27
    irb(main):003:0> 10 * 5
    => 50
    irb(main):004:0> 10**5
    => 100000
    irb(main):006:0> x = 1
    => 1
    irb(main):007:0> x + 59
    => 60
    irb(main):005:0> 50 / 5
    => 10
    irb(main):008:0> hi = "Hello, Mac!"
    => "Hello, Mac!"

You can also invoke a single program with irb. After running the program, irb exits. Let's call our hello.rb program:

    $ irb hello.rb
    hello.rb(main):001:0> #!/usr/bin/env ruby
    hello.rb(main):002:0*
    hello.rb(main):003:0* class Hello
    hello.rb(main):004:1> def initialize( hello )
    hello.rb(main):005:2> @hello = hello
    hello.rb(main):006:2> end
    hello.rb(main):007:1> def hello
    hello.rb(main):008:2> @hello
    hello.rb(main):009:2> end
    hello.rb(main):010:1> end
    => nil
    hello.rb(main):011:0>
    hello.rb(main):012:0* salute = Hello.new( "Hello, Mac!" )
    => #<Hello:0x319f20 @hello="Hello, Mac!">
    hello.rb(main):013:0> puts salute.hello
    Hello, Mac!
    => nil
    hello.rb(main):014:0> $

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