IRB: Document command evaluation history.

1 files changed, 12 insertions, 2 deletions

diff --git a/lib/irb.rb b/lib/irb.rb
index 6efb6c0e69..e95927f8ec 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -124,7 +124,7 @@ require "irb/version"
 # === History
 #
 # By default, irb will store the last 1000 commands you used in
-# <code>~/.irb_history</code>.
+# <code>IRB.conf[:HISTORY_FILE]</code> (<code>~/.irb_history</code> by default).
 #
 # If you want to disable history, add the following to your +.irbrc+:
 #
@@ -132,6 +132,14 @@ require "irb/version"
 #
 # See IRB::Context#save_history= for more information.
 #
+# The history of _resuls_ of commands evaluated is not stored by default,
+# but can be turned on to be stored with this +.irbrc+ setting:
+#
+#     IRB.conf[:EVAL_HISTORY] = <number>
+#
+# See IRB::Context#eval_history= and History class. The history of command
+# results is not permanently saved in any file.
+#
 # == Customizing the IRB Prompt
 #
 # In order to customize the prompt, you can change the following Hash:
@@ -274,7 +282,9 @@ require "irb/version"
 # <code>_</code>::
 #   The value command executed, as a local variable
 # <code>__</code>::
-#   The history of evaluated commands
+#   The history of evaluated commands. Available only if
+#   <code>IRB.conf[:EVAL_HISTORY]</code> is not +nil+ (which is the default).
+#   See also IRB::Context#eval_history= and IRB::History.
 # <code>__[line_no]</code>::
 #   Returns the evaluation value at the given line number, +line_no+.
 #   If +line_no+ is a negative, the return value +line_no+ many lines before