JIRB1.3(1)

💖 JIRB1.3(1) 💖

okay so bestie, this is the manual page for jirb1.3 — from the General Commands Manual. It's giving interactive JRuby energy, and we're about to break it all the way down. No cap. 🫶

---

🌸 NAME 🌸

jirb1.3 — interactive JRuby. That's it, that's the name. 💅

✨ SYNOPSIS ✨

jirb [options]

🦋 DESCRIPTION 🦋

irb stands for interactive JRuby. (Yes, the i is doing a lot of work, we love her.) irb is a tool to execute interactively JRuby expressions read from stdin. Use of jirb is easy if you know JRuby. Executing jirb, prompts are displayed as follows. Then, enter expression of ruby. Input is executed when it is syntacticaly completed.

Note: original says "syntacticaly" — we keep the spelling, bestie. 💀

$ jirb1.3
irb(main):001:0> 1+2
3
irb(main):002:0> class Foo
irb(main):003:1>  def foo
irb(main):004:2>    print 1
irb(main):005:2>  end
irb(main):006:1> end
nil
irb(main):007:0>

And, Readline extension module can be used with irb. Using Readline is the standard default action if Readline is installed. Periodt. ✨

💅 OPTIONS 💅

• -f — suppress read ~/.irbrc
• -m — bc mode (fraction or matrix are available)
• -d — set $DEBUG to true (same as ruby -d)
• -r load-module — same as ruby -r
• --inspect — uses inspect for output (the default except bc mode)
• --noinspect — doesn't uses inspect for output
• --readline — uses Readline extension module
• --noreadline — doesn't use Readline extension module
• --prompt prompt-mode — (no description given in original, but it's here)
• --prompt-mode prompt-mode — switches prompt mode. Pre-defined prompt modes are default, simple, xmp and inf-ruby
• --inf-ruby-mode — uses prompt appreciate for inf-ruby-mode on emacs. Suppresses --readline.
• --simple-prompt — simple prompt mode
• --noprompt — no prompt
• --tracer — display trace for each execution of commands.
• --back-trace-limit n — displays backtrace top n and tail n. The default value is 16.
• --irb_debug n — sets internal debug level to n (It shouldn't be used)
• -v, --version — prints the version of irb

🎀 CONFIGURATIONS 🎀

jirb reads ~/.irbrc when it is invoked. If ~/.irbrc doesn't exist jirb try to read in the order .irbrc, irb.rc, _irbrc then $irbrc. The following is alternative to the command line option. To use them type as follows in a jirb session.

IRB.conf[:IRB_NAME]="irb"
IRB.conf[:MATH_MODE]=false
IRB.conf[:USE_TRACER]=false
IRB.conf[:USE_LOADER]=false
IRB.conf[:IGNORE_SIGINT]=true
IRB.conf[:IGNORE_EOF]=false
IRB.conf[:INSPECT_MODE]=nil
IRB.conf[:IRB_RC] = nil
IRB.conf[:BACK_TRACE_LIMIT]=16
IRB.conf[:USE_LOADER] = false
IRB.conf[:USE_READLINE] = nil
IRB.conf[:USE_TRACER] = false
IRB.conf[:IGNORE_SIGINT] = true
IRB.conf[:IGNORE_EOF] = false
IRB.conf[:PROMPT_MODE] = :DEFALUT
IRB.conf[:PROMPT] = {...}
IRB.conf[:DEBUG_LEVEL]=0
IRB.conf[:VERBOSE]=true

Notice :DEFALUT — yes, that's a typo in the original. We keep it exactly. 💀

💖 Customizing prompt 💖

To customize the prompt you set a variable

IRB.conf[:PROMPT]

For example, describe as follows in .irbrc.

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

Then, invoke irb with the above prompt mode by

$ jirb1.3 --prompt my-prompt

Or add the following in .irbrc.

IRB.conf[:PROMPT_MODE] = :MY_PROMPT

Constants PROMPT_I, PROMPT_S and PROMPT_C specifies 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 degits 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_S => "%N(%m):%03n:%i%l ",

PROMPT_C => "%N(%m):%03n:%i* ",

RETURN => "%s\n"}

RETURN is used to printf.

🦋 Configuring subirb 🦋

The command line option or IRB.conf specify the default behavior of (sub)irb. On the other hand, each conf of in the next sction 6. Command is used to individually configure (sub)irb. If proc is set to IRB.conf[:IRB_RC], its subirb will be invoked after execution of that proc under giving the context of irb as its argument. By this mechanism each subirb can be configured.

🌈 Command 🌈

For irb commands, both simple name and irb_-prefixed name are prepared.

• exit, quit, irb_exit — Quits (sub)irb. if you've done cb (see below), exit from the binding mode.
• conf, irb_context — Displays current configuration. Modifying the configuration is achieved by sending message to conf.
• conf.back_trace_limit — Sets display lines of backtrace as top n and tail n. The default value is 16.
• conf.debug_level = N — Sets debug level of irb.
• conf.ignore_eof = true/false — Whether ^D (control-d) will be ignored or not. If false is set, ^D means quit.
• conf.ignore_sigint= true/false — Whether ^C (control-c) will be ignored or not. If false is set, ^D means quit. If true,
  • during input: cancel inputing then return to top level.
  • during execute: abondon current execution.
• conf.inf_ruby_mode = true/false — Whether inf-ruby-mode or not. The default value is false.
• conf.inspect_mode = true/false/nil — Specifies inspect mode. true: display inspect false: display to_s nil: inspect mode in non math mode, non inspect mode in math mode.
• conf.irb_level — The level of cb.
• conf.math_mode — Whether bc mode or not.
• conf.use_loader = true/false — Whether irb's own file reader method is used when load/require or not. This mode is globaly affected (irb wide).
• conf.prompt_c — prompt for a continuating statement (e.g, immediately after of if)
• conf.prompt_i — standard prompt
• conf.prompt_s — prompt for a continuating string
• conf.rc — Whether ~/.irbrc is read or not.
• conf.use_prompt = true/false — Prompting or not.
• conf.use_readline = true/false/nil — Whether readline is used or not. true: uses false: doesn't use nil: intends to use readline except for inf-reuby-mode (default)
• conf.verbose=T/F — Whether verbose messages are display or not.
• cb, irb_change_binding [obj] — Enter new binding which has a distinct scope of local variables. If obj is given, obj will be self.
• irb [obj] — Invoke subirb. If obj is given, obj will be self.
• jobs, irb_jobs — List of subirb
• fg n, irb_fg n — Switch into specified subirb. The following is candidates of n:
  • irb number
  • thhread
  • irb object
  • self(obj which is specified of irb obj)
• kill n, irb_kill n — Kill subirb. The means of n is as same as the case of irb_fg.

⭐ System variable ⭐

• _ — The latest value of evaluation (it is local)

🌟 Session Example 🌟

$ jirb1.3
irb(main):001:0> irb                        # invoke subirb
irb#1(main):001:0> jobs                     # list of subirbs
#0->irb on main (#<Thread:0x400fb7e4> : stop)
#1->irb#1 on main (#<Thread:0x40125d64> : running)
nil
irb#1(main):002:0> fg 0                     # switch job
nil
irb(main):002:0> class Foo;end
nil
irb(main):003:0> irb Foo                    # invoke subirb which has the
#              context of Foo
irb#2(Foo):001:0> def foo                   # define Foo#foo
irb#2(Foo):002:1>   print 1
irb#2(Foo):003:1> end
nil
irb#2(Foo):004:0> fg 0                      # switch job
nil
irb(main):004:0> jobs                       # list of job
#0->irb on main (#<Thread:0x400fb7e4> : running)
#1->irb#1 on main (#<Thread:0x40125d64> : stop)
#2->irb#2 on Foo (#<Thread:0x4011d54c> : stop)
nil
irb(main):005:0> Foo.instance_methods       # Foo#foo is defined asurely
["foo"]
irb(main):006:0> fg 2                       # switch job
nil
irb#2(Foo):005:0> def bar                   # define Foo#bar
irb#2(Foo):006:1>  print "bar"
irb#2(Foo):007:1> end
nil
irb#2(Foo):010:0>  Foo.instance_methods
["bar", "foo"]
irb#2(Foo):011:0> fg 0
nil
irb(main):007:0> f = Foo.new
#<Foo:0x4010af3c>
irb(main):008:0> irb f                      # invoke subirb which has the
#  context of f (instance of Foo)
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)
nil
irb#3(#<Foo:0x4010af3c>):002:0> foo         # evaluate f.foo
1nil
irb#3(#<Foo:0x4010af3c>):003:0> bar         # evaluate f.bar
barnil
irb#3(#<Foo:0x4010af3c>):004:0> kill 1, 2, 3# kill job
nil
irb(main):009:0> jobs
#0->irb on main (#<Thread:0x400fb7e4> : running)
nil
irb(main):010:0> exit                       # exit

💀 Restrictions 💀

Because irb evaluates the inputs immediately after the input is syntactically completed, irb gives slight different results than directly using ruby. Known differences are pointed out here.

🌸 Declaration of the local variable 🌸

The following causes an error in ruby:

eval "foo = 0"
foo
--
-:2: undefined local variable or method `foo' for #<Object:0x40283118> (NameError)
---
NameError

Though, the above will successfully done by irb.

>> eval "foo = 0"
=> 0
>> foo
=> 0

Ruby evaluates a code after reading entire of code and determination of the scope of local variables. On the other hand, irb do immediately. More precisely, irb evaluate at first

evel "foo = 0"

then foo is defined on this timing. It is because of this incompatibility. If you'd like to detect those differences, begin...end can be used:

>> begin
?>   eval "foo = 0"
>>   foo
>> end
NameError: undefined local variable or method `foo' for #<Object:0x4013d0f0>
(irb):3
(irb_local_binding):1:in `eval'

🦋 Here-document 🦋

Implementation of Here-document is incomplete.

💎 Symbol 💎

okay bestie, real talk for a sec because this one is lowkey sneaky 👀

irb can not always recognize a symbol as to be a Symbol. like, it wants to, it's trying its best, but sometimes it just doesn't clock it 🫠

concretely — here's the exact situation — an expression has completed, however irb regards it as a continuation line. so you're sitting there like "girl the expression is DONE" and irb is sitting there like "and we continue…" 😭

no cap, that's the whole thing: your expression is finished, but irb treats it as a continuation line. it's not a you problem, it's just how it is. 💅

---

and that's a wrap on the whole page, bestie 💖 this one is dated April 2007 and it goes by JIRB1.3(1) — iconic behavior from a manpage that's been serving since before most of us could type 🎀✨

go forth and slay your irb session, you absolute main character 👑🦋