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jirb1.3 - interactive JRuby


jirb [options]


irb stands for `interactive JRuby'. 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. A input is executed when
it is syntacticaly completed.

$ jirb1.3
irb(main):001:0> 1+2
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

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


-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'

uses `inspect' for output (the default except bc mode)

doesn't uses inspect for output

uses Readline extension module

doesn't use Readline extension module

--prompt prompt-mode

--prompt-mode prompt-mode
switches prompt mode. Pre-defined prompt modes are `default', `simple', `xmp' and

uses prompt appreciate for inf-ruby-mode on emacs. Suppresses --readline.

simple prompt mode

no prompt

display trace for each execution of commands.

--back-trace-limit n
displayes 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


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

IRB.conf[:IRB_RC] = nil
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] = {...}

Customizing prompt

To costomize the prompt you set a variable


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'.


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 ommited
%NNn line number.
%% %
For instance, the default prompt mode is defined as follows:

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.

Configurating 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 configurate
(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 aregument. By this mechanism each
subirb can be configurated.


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. Modifing the configuration is achieved by sending
message to `conf'.

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
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.

The level of cb.

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).

prompt for a continuating statement (e.g, immediately after of `if')

standard prompt

prompt for a continuating string

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: doen't use nil: intends to use
readline except for inf-reuby-mode (default)

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
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)
irb#1(main):002:0> fg 0 # switch job
irb(main):002:0> class Foo;end
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
irb#2(Foo):004:0> fg 0 # switch job
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)
irb(main):005:0> Foo.instance_methods # Foo#foo is defined asurely
irb(main):006:0> fg 2 # switch job
irb#2(Foo):005:0> def bar # define Foo#bar
irb#2(Foo):006:1> print "bar"
irb#2(Foo):007:1> end
irb#2(Foo):010:0> Foo.instance_methods
["bar", "foo"]
irb#2(Foo):011:0> fg 0
irb(main):007:0> f = Foo.new
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)
irb#3(#<Foo:0x4010af3c>):002:0> foo # evaluate f.foo
irb#3(#<Foo:0x4010af3c>):003:0> bar # evaluate f.bar
irb#3(#<Foo:0x4010af3c>):004:0> kill 1, 2, 3# kill job
irb(main):009:0> jobs
#0->irb on main (#<Thread:0x400fb7e4> : running)
irb(main):010:0> exit # exit


Because irb evaluates the inputs immediately after the imput is syntactically completed,
irb gives slight different result than directly use ruby. Known difference is pointed out

Declaration of the local variable

The following causes an error in ruby:

eval "foo = 0"
-:2: undefined local variable or method `foo' for #<Object:0x40283118> (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_local_binding):1:in `eval'


Implementation of Here-document is incomplete.


Irb can not always recognize a symbol as to be Symbol. Concretely, an expression have
completed, however Irb regard it as continuation line.

April 2007 JIRB1.3(1)

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