Man Linux: Main Page and Category List


       irb1.8 - interactive ruby


       irb [options]


       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

           $ irb1.8
           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 `inf-ruby'

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

              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


       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_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_MODE] = :DEFALUT
           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

           $ irb1.8 --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.


       For irb  commands,  both  simple  name  and  `irb_'-prefixed  name  are

       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 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.

              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

              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

           $ irb1.8
           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 =
           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
           irb#3(#<Foo:0x4010af3c>):003:0> bar         # evaluate
           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 here.

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.

                                 December 2002