Mastering IRB

Command line options

Usage:  irb.rb [options] [programfile] [arguments]
  -f                Suppress read of ~/.irbrc
  -d                Set $DEBUG to true (same as `ruby -d`)
  -r load-module    Same as `ruby -r`
  -I path           Specify $LOAD_PATH directory
  -U                Same as `ruby -U`
  -E enc            Same as `ruby -E`
  -w                Same as `ruby -w`
  -W[level=2]       Same as `ruby -W`
  --inspect         Use `inspect` for output (default except for bc mode)
  --noinspect       Don't use inspect for output
  --multiline       Use multiline editor module
  --nomultiline     Don't use multiline editor module
  --singleline      Use singleline editor module
  --nosingleline    Don't use singleline editor module
  --colorize        Use colorization
  --nocolorize      Don't use colorization
  --prompt prompt-mode
  --prompt-mode prompt-mode
                    Switch prompt mode. Pre-defined prompt modes are
                    `default`, `simple`, `xmp` and `inf-ruby`
  --inf-ruby-mode   Use prompt appropriate for inf-ruby-mode on emacs.
                    Suppresses --multiline and --singleline.
  --simple-prompt   Simple prompt mode
  --noprompt        No prompt mode
  --tracer          Display trace for each execution of commands.
  --back-trace-limit n
                    Display backtrace top n and tail n. The default
                    value is 16.
  -v, --version     Print the version of irb

Configuration

IRB reads from ~/.irbrc when it’s invoked.

If ~/.irbrc doesn’t exist, irb will try to read in the following order:

.irbrc
irb.rc
_irbrc
$irbrc

The following are alternatives to the command line options. To use them type as follows in an irb session:

IRB.conf[:IRB_NAME]="irb"
IRB.conf[:INSPECT_MODE]=nil
IRB.conf[:IRB_RC] = nil
IRB.conf[:BACK_TRACE_LIMIT]=16
IRB.conf[:USE_LOADER] = false
IRB.conf[:USE_MULTILINE] = nil
IRB.conf[:USE_SINGLELINE] = nil
IRB.conf[:USE_COLORIZE] = true
IRB.conf[:USE_TRACER] = false
IRB.conf[:IGNORE_SIGINT] = true
IRB.conf[:IGNORE_EOF] = false
IRB.conf[:PROMPT_MODE] = :DEFAULT
IRB.conf[:PROMPT] = {...}

Auto indentation

To disable auto-indent mode in irb, add the following to your .irbrc:

IRB.conf[:AUTO_INDENT] = false

Autocompletion

To enable autocompletion for irb, add the following to your .irbrc:

require 'irb/completion'

History

By default, irb will store the last 1000 commands you used in IRB.conf[:HISTORY_FILE] (~/.irb_history by default).

If you want to disable history, add the following to your .irbrc:

IRB.conf[:SAVE_HISTORY] = nil

See IRB::Context#save_history= for more information.

The history of results 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:

IRB.conf[:PROMPT]

This example can be used in your .irbrc

IRB.conf[:PROMPT][:MY_PROMPT] = { # name of prompt mode
  :AUTO_INDENT => false,          # disables auto-indent mode
  :PROMPT_I =>  ">> ",            # simple prompt
  :PROMPT_S => nil,               # prompt for continuated strings
  :PROMPT_C => nil,               # prompt for continuated statement
  :RETURN => "    ==>%s\n"        # format to return value
}

IRB.conf[:PROMPT_MODE] = :MY_PROMPT

Or, invoke irb with the above prompt mode by:

irb --prompt my-prompt

Constants PROMPT_I, PROMPT_S and PROMPT_C specify the format. In the prompt specification, some special strings are available:

%N    # command name which is running
%m    # to_s of main object (self)
%M    # inspect of main object (self)
%l    # type of string(", ', /, ]), `]' is inner %w[...]
%NNi  # indent level. NN is digits and means as same as printf("%NNd").
      # It can be omitted
%NNn  # line number.
%%    # %

For instance, the default prompt mode is defined as follows:

IRB.conf[:PROMPT_MODE][:DEFAULT] = {
  :PROMPT_I => "%N(%m):%03n:%i> ",
  :PROMPT_N => "%N(%m):%03n:%i> ",
  :PROMPT_S => "%N(%m):%03n:%i%l ",
  :PROMPT_C => "%N(%m):%03n:%i* ",
  :RETURN => "%s\n" # used to printf
}

irb comes with a number of available modes:

# :NULL:
#   :PROMPT_I:
#   :PROMPT_N:
#   :PROMPT_S:
#   :PROMPT_C:
#   :RETURN: |
#     %s
# :DEFAULT:
#   :PROMPT_I: ! '%N(%m):%03n:%i> '
#   :PROMPT_N: ! '%N(%m):%03n:%i> '
#   :PROMPT_S: ! '%N(%m):%03n:%i%l '
#   :PROMPT_C: ! '%N(%m):%03n:%i* '
#   :RETURN: |
#     => %s
# :CLASSIC:
#   :PROMPT_I: ! '%N(%m):%03n:%i> '
#   :PROMPT_N: ! '%N(%m):%03n:%i> '
#   :PROMPT_S: ! '%N(%m):%03n:%i%l '
#   :PROMPT_C: ! '%N(%m):%03n:%i* '
#   :RETURN: |
#     %s
# :SIMPLE:
#   :PROMPT_I: ! '>> '
#   :PROMPT_N: ! '>> '
#   :PROMPT_S:
#   :PROMPT_C: ! '?> '
#   :RETURN: |
#     => %s
# :INF_RUBY:
#   :PROMPT_I: ! '%N(%m):%03n:%i> '
#   :PROMPT_N:
#   :PROMPT_S:
#   :PROMPT_C:
#   :RETURN: |
#     %s
#   :AUTO_INDENT: true
# :XMP:
#   :PROMPT_I:
#   :PROMPT_N:
#   :PROMPT_S:
#   :PROMPT_C:
#   :RETURN: |2
#         ==>%s

Restrictions

Because irb evaluates input immediately after it is syntactically complete, the results may be slightly different than directly using Ruby.

IRB Sessions

IRB has a special feature, that allows you to manage many sessions at once.

You can create new sessions with Irb.irb, and get a list of current sessions with the jobs command in the prompt.

Commands

JobManager provides commands to handle the current sessions:

jobs    # List of current sessions
fg      # Switches to the session of the given number
kill    # Kills the session with the given number

The exit command, or ::irb_exit, will quit the current session and call any exit hooks with IRB.irb_at_exit.

A few commands for loading files within the session are also available:

source: Loads a given file in the current session and displays the source lines, see IrbLoader#source_file
irb_load: Loads the given file similarly to Kernel#load, see IrbLoader#irb_load
irb_require: Loads the given file similarly to Kernel#require

Configuration

The command line options, or IRB.conf, specify the default behavior of Irb.irb.

On the other hand, each conf in IRB@Command+line+options is used to individually configure IRB.irb.

If a proc is set for IRB.conf[:IRB_RC], its will be invoked after execution of that proc with the context of the current session as its argument. Each session can be configured using this mechanism.

Session variables

There are a few variables in every Irb session that can come in handy:

_: The value command executed, as a local variable
__: The history of evaluated commands. Available only if IRB.conf[:EVAL_HISTORY] is not nil (which is the default). See also IRB::Context#eval_history= and IRB::History.
__[line_no]: 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 the most recent return value.

Example using IRB Sessions

# invoke a new session
irb(main):001:0> irb
# list open sessions
irb.1(main):001:0> jobs
  #0->irb on main (#<Thread:0x400fb7e4> : stop)
  #1->irb#1 on main (#<Thread:0x40125d64> : running)

# change the active session
irb.1(main):002:0> fg 0
# define class Foo in top-level session
irb(main):002:0> class Foo;end
# invoke a new session with the context of Foo
irb(main):003:0> irb Foo
# define Foo#foo
irb.2(Foo):001:0> def foo
irb.2(Foo):002:1>   print 1
irb.2(Foo):003:1> end

# change the active session
irb.2(Foo):004:0> fg 0
# list open sessions
irb(main):004:0> jobs
  #0->irb on main (#<Thread:0x400fb7e4> : running)
  #1->irb#1 on main (#<Thread:0x40125d64> : stop)
  #2->irb#2 on Foo (#<Thread:0x4011d54c> : stop)
# check if Foo#foo is available
irb(main):005:0> Foo.instance_methods #=> [:foo, ...]

# change the active session
irb(main):006:0> fg 2
# define Foo#bar in the context of Foo
irb.2(Foo):005:0> def bar
irb.2(Foo):006:1>  print "bar"
irb.2(Foo):007:1> end
irb.2(Foo):010:0>  Foo.instance_methods #=> [:bar, :foo, ...]

# change the active session
irb.2(Foo):011:0> fg 0
irb(main):007:0> f = Foo.new  #=> #<Foo:0x4010af3c>
# invoke a new session with the context of f (instance of Foo)
irb(main):008:0> irb f
# list open sessions
irb.3(<Foo:0x4010af3c>):001:0> jobs
  #0->irb on main (#<Thread:0x400fb7e4> : stop)
  #1->irb#1 on main (#<Thread:0x40125d64> : stop)
  #2->irb#2 on Foo (#<Thread:0x4011d54c> : stop)
  #3->irb#3 on #<Foo:0x4010af3c> (#<Thread:0x4010a1e0> : running)
# evaluate f.foo
irb.3(<Foo:0x4010af3c>):002:0> foo #=> 1 => nil
# evaluate f.bar
irb.3(<Foo:0x4010af3c>):003:0> bar #=> bar => nil
# kill jobs 1, 2, and 3
irb.3(<Foo:0x4010af3c>):004:0> kill 1, 2, 3
# list open sessions, should only include main session
irb(main):009:0> jobs
  #0->irb on main (#<Thread:0x400fb7e4> : running)
# quit irb
irb(main):010:0> exit

IRB Reference

Ruby 2.7 Reference SAVE UKRAINE

Mastering IRB

Command line options

Configuration

Auto indentation

Autocompletion

History

Customizing the IRB Prompt

Restrictions

IRB Sessions

Commands

Configuration

Session variables

Example using IRB Sessions