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irb (1)
  • >> irb (1) ( Linux man: Команды и прикладные программы пользовательского уровня )

    What is irb?

    irb stands for `interactive ruby'. irb is a tool to execute interactively ruby expressions read from stdin.  


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


    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.

        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. 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'.

    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
        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 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.



    What is irb?
    Command line option
    Customizing prompt
    Configurating subirb
    System variable
    Session Example
    Declaration of the local variable

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