irb-beta(1)                                                        irb-beta(1)

What is irb?

       irb  stands  for  ‘interactive ruby’. irb is a tool to execute interac-
       tively ruby expressions read from stdin.


           % ruby -r irb -e0
           % irb
       Either of the aboves. In the former style, options can be specified  as
           % ruby -r irb -e0 -- -v


       Use  of  irb is easy if you know ruby.  Executing irb, prompts are dis-
       played as follows. Then, enter expression of ruby. A input is  executed
       when it is syntacticaly completed.
           dim% irb
           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.

Command line option

           irb.rb [options] file_name opts
           -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
           ‘defalut’, ‘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


       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
           % irb --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.  Com-
       mand’  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 mecha-
       nism each subirb can be configurated.


       For irb commands, both simple name and ‘irb_’-prefixed  name  are  pre-

       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

           dim% ruby irb.rb
           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 syntac-
       tically  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 incompatibil-
       ity.   If  you’d  like  to detect those differences, begin...end can be
           >> 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.

                                   May 2001                        irb-beta(1)

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