Irb: How to Start an Interactive Ruby Session with Pre-Loaded Classes

IRb: how to start an interactive ruby session with pre-loaded classes

I'm not sure it's possible to 'flush' a session. However, you can load your classes like this:

irb -r 'hello.rb' -r 'hello_objects.rb'

How to create custom IRB file to load a Ruby project's files, gems and dependencies?

Very simple, actually:

#!/usr/bin/env ruby
require "bundler/setup"
# ...
# everything else you need
# ...
require "irb"
IRB.start

When you start IRB using IRB.start, you will have available everything that's been loaded/initialised before it.

automatically load project's environment to irb

Your project should have one file which loads the environment. Assuming your project is in lib/project.rb then simply:

$ irb -Ilib -rproject

Ruby / IRB environment issue on MacOSX

I didn't know there was a "help" command, but apparently it has dependency on FileUtils, probably to load help files. "help" is loading its requirements into the IRB session.

>> before = ObjectSpace.each_object.map { |i| i.class }.uniq
=> [Regexp, String, Array, Class, Hash, Module, Proc, MatchData, File, Binding, NoMemoryError, Float, SystemStackError, fatal, Bignum, Object, IO, Thread, ThreadGroup, IRB::Locale, IRB::Notifier::LeveledNotifier, IRB::Notifier::CompositeNotifier, IRB::StdioOutputMethod, IRB::Notifier::NoMsgNotifier, Enumerable::Enumerator, RubyToken::TkNL, RubyToken::TkEND, RubyToken::TkBITOR, RubyToken::TkIDENTIFIER, RubyToken::TkDOT, RubyToken::TkRBRACE, RubyToken::TkSPACE, RubyToken::TkfLBRACE, RubyToken::TkCONSTANT, RubyToken::TkASSIGN, IRB::SLex::Node, IRB::SLex, RubyLex, IRB::ReadlineInputMethod, IRB::WorkSpace, IRB::Context, IRB::Irb]
>> help
=> nil
>> after  = ObjectSpace.each_object.map { |i| i.class }.uniq
=> [Regexp, String, MatchData, Array, Class, RI::ClassEntry, RI::MethodEntry, Hash, Module, Dir, Proc, File, Binding, NoMemoryError, Float, SystemStackError, fatal, Bignum, Object, IO, Thread, ThreadGroup, IRB::Locale, Range, IRB::Notifier::LeveledNotifier, IRB::Notifier::CompositeNotifier, IRB::StdioOutputMethod, IRB::Notifier::NoMsgNotifier, YAML::Syck::Resolver, Gem::ConfigFile, RubyToken::TkNL, RubyToken::TkIDENTIFIER, IRB::SLex::Node, IRB::SLex, RubyLex, IRB::ReadlineInputMethod, IRB::WorkSpace, IRB::Context, IRB::Irb, RI::TopLevelEntry, RI::RiReader, GetoptLong, RI::RiCache, RI::Options, RiDriver, Rational, Date::Infinity, Enumerable::Enumerator, RubyToken::TkRBRACE, DefaultDisplay, RI::TextFormatter]
>> after == before
=> false
>> after - before
=> [RI::ClassEntry, RI::MethodEntry, Dir, Range, YAML::Syck::Resolver, Gem::ConfigFile, RI::TopLevelEntry, RI::RiReader, GetoptLong, RI::RiCache, RI::Options, RiDriver, Rational, Date::Infinity, DefaultDisplay, RI::TextFormatter]

It loads the classes in after - before. Where is FileUtils you say? I think its a module that is part of Dir, but I am not 100% on that.

How to run IRB.start in context of current class

I'd suggest trying this in ripl, an irb alternative. The above example works:

a = 'hello'
require 'ripl'
Ripl.start :binding => binding

Note that local variables work because your passing the current binding with the :binding option.

You could possibly do the same in irb, but since it's poorly documented and untested, your chances of doing it cleanly are slim to none.

automatically load project's environment to irb

Your project should have one file which loads the environment. Assuming your project is in lib/project.rb then simply:

$ irb -Ilib -rproject

Can you 'require' ruby file in irb session, automatically, on every command?

I usually create a simple function like this:

def reload
    load 'myscript.rb'
    # Load any other necessary files here ...
end

With that, a simple reload will re-import all of the scripts that I'm working on. It's not automatic, but it's the closest thing that I've been able to come up with.

You may be able to override method_missing to call this function automatically when your object is invoked with a method that doesn't exist. I've never tried it myself, though, so I can't give any specific advice. It also wouldn't help if you're calling a method that already exists but has simply been modified.

In my own laziness, I've gone as far as mapping one of the programmable buttons on my mouse to the key sequence "reload<enter>". When I'm using irb, all it takes is the twitch of a pinky finger to reload everything. Consequently when I'm not using irb, I end up with the string "reload" inserted in documents unintentionally (but that's a different problem entirely).

What's the point of an interactive Ruby subshell?

So far I've seen three usefull things irb subsessions can do for you:

1. undefine local variables
2. change self of an irb session
3. irb is a part of a great set of tools

undefine local variables

The nested irb starts a new subsession in which all local variables (not classes, modules etc.) are not defined any more.

irb(main):001:0> a = 1
#=> 1
irb(main):002:0> irb
irb#1(main):001:0> a
  NameError: undefined local variable or method `a' for main:Object from (irb#1):1

change self for an irb session

irb(main):001:0> self
#=> main
irb(main):002:0> irb "Hello World"
irb#1(Hello World):001:0> self
#=> "Hello World"
irb#1(Hello World):002:0> length
#=> 11

Note: This is also known as "change binding" of an irb session.

By the way: It's possible to change the binding without opening a subsession (cb, irb_change-binding both do that for you). But it's more convenient to get back to the old binding with subsession.

The best thing is, that irb is just one of a useful set of commands

• irb: start a new subsession
• jobs: list subsessions
• fg: switch to a subsession
• kill: kill a subsession

See this insteresting SO answer for details.

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