1 files changed, 51 insertions, 0 deletions
diff --git a/lib/irb/command/show_doc.rb b/lib/irb/command/show_doc.rb
new file mode 100644
index 0000000000..8a2188e4eb
--- /dev/null
+++ b/lib/irb/command/show_doc.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+module IRB
+  module Command
+    class ShowDoc < Base
+      include RubyArgsExtractor
+
+      category "Context"
+      description "Look up documentation with RI."
+
+      help_message <<~HELP_MESSAGE
+        Usage: show_doc [name]
+
+        When name is provided, IRB will look up the documentation for the given name.
+        When no name is provided, a RI session will be started.
+
+        Examples:
+
+          show_doc
+          show_doc Array
+          show_doc Array#each
+
+      HELP_MESSAGE
+
+      def execute(arg)
+        # Accept string literal for backward compatibility
+        name = unwrap_string_literal(arg)
+        require 'rdoc/ri/driver'
+
+        unless ShowDoc.const_defined?(:Ri)
+          opts = RDoc::RI::Driver.process_args([])
+          ShowDoc.const_set(:Ri, RDoc::RI::Driver.new(opts))
+        end
+
+        if name.nil?
+          Ri.interactive
+        else
+          begin
+            Ri.display_name(name)
+          rescue RDoc::RI::Error
+            puts $!.message
+          end
+        end
+
+        nil
+      rescue LoadError, SystemExit
+        warn "Can't display document because `rdoc` is not installed."
+      end
+    end
+  end
+end