# RI¶ ↑

`ri` is a tool that allows Ruby documentation to be viewed on the command-line.

You can use `ri` to look up information from either the command line or interactively. When you run `ri` without any arguments it will launch in interactive mode. In interactive mode you can tab-complete class and method names.

## Usage¶ ↑

To see information for a class, do:

    ri ClassName

For example, for the Array class, do:

    ri Array

To see information on a method on a class, do:

    ri ClassName.method

This will show both instance and class methods. For example, the IO class defines both IO::read and IO#read:

    ri IO.read

To see information for an instance method, do:

    ri ClassName#method_name

For example, for Array's `join` method, do:

    ri Array#join

To see information for a class method, do:

    ri ClassName::method_name

For example, for Module's `private` method, do:

    ri Module::private

To read documentation for all `read` methods, do:

    ri read

## Options¶ ↑

`ri` supports a variety of options, all of which can be viewed via `--help`. Of particular interest, are:

`-f`

  Outputs ri data using the selected formatter. You can see the available formatters in `ri --help`

`-T`

  Send output to stdout, rather than to a pager.

All options also can be specified through the `RI` environment variable. Command-line options always override those specified in the `RI` environment variable.

The `RI_PAGER` environment variable allows you to choose a particular pager or particular options for your pager.