Provided by: ruby1.9.1_1.9.3.484-2ubuntu1.14_amd64 
NAME
irb1.9.1 - interactive ruby
SYNOPSIS
irb [options]
DESCRIPTION
irb stands for `interactive ruby'. irb is a tool to execute interactively ruby expressions
read from stdin. Use of irb is easy if you know ruby. Executing irb, prompts are
displayed as follows. Then, enter expression of ruby. A input is executed when it is
syntacticaly completed.
$ irb1.9.1
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 extesion module can be used with irb. Using Readline is the standard default
action if Readline is installed.
OPTIONS
-f suppress read ~/.irbrc
-m bc mode (fraction or matrix are available)
-d set $DEBUG to true (same as `ruby -d')
-r load-module
same as `ruby -r'
--inspect
uses `inspect' for output (the default except bc mode)
--noinspect
doesn't uses inspect for output
--readline
uses Readline extension module
--noreadline
doesn't use Readline extension module
--prompt prompt-mode
--prompt-mode prompt-mode
switches prompt mode. Pre-defined prompt modes are `default', `simple', `xmp' and
`inf-ruby'
--inf-ruby-mode
uses prompt appreciate for inf-ruby-mode on emacs. Suppresses --readline.
--simple-prompt
simple prompt mode
--noprompt
no prompt
--tracer
display trace for each execution of commands.
--back-trace-limit n
displayes backtrace top n and tail n. The default value is 16.
--irb_debug n
sets internal debug level to n (It shouldn't be used)
-v, --version
prints the version of irb
CONFIGURATIONS
irb reads `~/.irbrc' when it is invoked. If `~/.irbrb' doesn't exist irb try to read in
the order `.irbrc', `irb.rc', `_irbrc' then `$irbrc'. The following is altanative to the
command line option. To use them type as follows in an irb 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
Customizing prompt
To costomize 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
$ irb1.9.1 --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 ommited
%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.
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.
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. Modifing 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: doen'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
$ irb1.9.1
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 imput is syntactically completed,
irb gives slight different result than directly use ruby. Known difference is 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
Irb can not always recognize a symbol as to be Symbol. Concretely, an expression have
completed, however Irb regard it as continuation line.
December 2002 IRB1.9(1)