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Ruby用户指南 3、开始 4、简单的例子 5、字符串 6、正则表达式 7、数组 8、回到那些简单的例子 9、流程控制 10、迭代器 11、面向对象思维 12、方法 13、类 14、继承 15、重载方法 16、访问控制 17、单态方法 18、模块 19、过程对象 20、变量 21、全局变量 22、实变量 23、局部变量 24、类常量 25、异常处理:rescue 26、异常处理:ensure 27、存取器 28、对象的初始化 29、杂项 RGSS入门教程 1、什么是RGSS 2、开始:最简单的脚本 3、数据类型:数字 4、数据类型:常量与变量 5、数据类型:字符串 6、控制语句:条件分歧语句 7、控制语句:循环 8、函数 9、对象与类 10、显示图片 11、数组 12、哈希表(关联数组) 13、类 14、数据库 15、游戏对象 16、精灵的管理 17、窗口的管理 18、活动指令 19、场景类 Programming Ruby的翻译 Programming Ruby: The Pragmatic Programmer's Guide 前言 Roadmap Ruby.new 类,对象和变量 容器Containers,块Blocks和迭代Iterators 标准类型 深入方法 表达式Expressions 异常,捕捉和抛出(已经开始,by jellen) 模块 基本输入输出 线程和进程 当遭遇挫折 Ruby和它的世界 Ruby和Web开发 Ruby Tk Ruby 和微软的 Windows 扩展Ruby Ruby语言 (by jellen) 类和对象 (by jellen) Ruby安全 反射Reflection 内建类和方法 标准库 OO设计 网络和Web库 Windows支持 内嵌文档 交互式Ruby Shell 支持 Ruby参考手册 Ruby首页 卷首语 Ruby的启动 环境变量 对象 执行 结束时的相关处理 线程 安全模型 正则表达式 字句构造 程序 变量和常数 字面值 操作符表达式 控制结构 方法调用 类/方法的定义 内部函数 内部变量 内部常数 内部类/模块/异常类 附加库 Ruby变更记录 ruby 1.6 特性 ruby 1.7 特性 Ruby术语集 Ruby的运行平台 pack模板字符串 sprintf格式 Marshal格式 Ruby FAQ Ruby的陷阱
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Interactive Ruby Shell



Back on page 124 we introduced irb, a Ruby module that lets you enter Ruby programs interactively and see the results immediately. This appendix goes into more detail on using and customizing irb.

Command Line

irbis run from the command line.

irb[irb-options][ruby_script][options]

The command-line options for irb are listed in Table B.1 on page 518. Typically, you'll run irb with no options, but if you want to run a script and watch the blow-by-blow description as it runs, you can provide the name of the Ruby script and any options for that script.
irb command-line options
Option Description
-f Suppress reading~/.irbrc.
-m Math mode (fraction and matrix support is available).
-d Set$DEBUGto true (same as ``ruby -d'').
-r load-module Same as ``ruby -r''.
--inspect Use ``inspect'' for output (the default, unless in math mode).
--noinspect Do not use inspect for output.
--readline UseReadlineextension module.
--noreadline Do not useReadlineextension module.
--promptprompt-mode Switch prompt mode. Predefined prompt modes are ``default'', ``simple'', ``xmp'', and ``inf-ruby''.
--prompt-modeprompt-mode Same as--prompt.
--inf-ruby-mode Sets up irb to run ininf-ruby-modeunder Emacs. Changes the prompt and suppresses--readline.
--simple-prompt Simple prompt mode.
--noprompt Do not display a prompt.
--tracer Display trace for execution of commands.
--back-trace-limit n Display backtrace information using the top n and last n entries. The default value is 16.
--irb_debug n Set internal debug level to n (only for irb development).
-v, --version Print the version of irb.

Initialization File

irb uses an initialization file in which you can set commonly used options or execute any required Ruby statements. When irb is run, it will try to load an initialization file from one of the following sources in order: ~/.irbrc, .irbrc, irb.rc, _irbrc, and $irbrc.

Within the initialization file you may run any arbitrary Ruby code. You can also set any of the configuration values that correspond to command-line arguments as shown in Table B.2 on page 518.
irb configuration values

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] = :DEFAULT IRB.conf[:PROMPT] = { ... }
IRB.conf[:DEBUG_LEVEL] = 0 IRB.conf[:VERBOSE] = true

As an interesting twist on configuring irb, you can set IRB.conf[:IRB_RC]to a Procobject. This proc will be invoked whenever the irb context is changed, and will receive that new context as a parameter. You can use this facility to change the configuration dynamically based on the context.

Commands

At the irb prompt, you can enter any valid Ruby expression and see the results. You can also use any of the following commands to control the irb session.

exit, quit, irb_exit
Quits this irb session or subsession. If you've used cbto change bindings (see below), exits from this binding mode.

conf, irb_context
Displays current configuration. Modifying the configuration is achieved by invoking methods of conf.

conf.back_trace_limit n
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
Specifies the behavior of an end of file received on input. If true, it will be ignored; otherwise, it will quit irb.

conf.ignore_sigint= true/false
Specifies the behavior of ^C (control-c). If false, ^C will quit irb. If true, ^C during input will cancel input and return to the top level; during execution, ^C will abort the current operation.

conf.inf_ruby_mode = true/false
If true, changes the prompt and disables readline support, allowing irb to work with inf-ruby-mode. [inf-ruby-modeallows Emacs users to interact with Ruby while editing programs. See the fileinf_ruby.elin themiscdirectory of the distribution for more details.]The default value is false.

conf.inspect_mode = true/false/nil
Specifies inspect mode according to the following values:

true Display inspect (default).
false Display to_s.
nil Inspect mode in non-math mode, non-inspect mode in math mode.

conf.irb_level
Displays the current binding level (see cb).

conf.math_mode
Displays whether or not Ruby is in math mode.

conf.use_loader = true/false
Specifies whether or not irb's own file reader method is used with load/ require.

conf.prompt_c
The prompt for a continuing statement (for example, immediately after an ``if'').

conf.prompt_i
The standard, top-level prompt.

conf.prompt_s
The prompt for a continuing string.

conf.rc = true/false
Specifies whether or not to use the initialization file ~/.irbrc.

conf.use_prompt = true/false
Specifies whether or not to display prompts.

conf.use_readline = true/false/nil
Specifies whether or not to use Readline according to the following values:

true Use Readline.
false Do not use Readline.
nil Use Readline except forinf-ruby-mode(default).

conf.verbose=true/false
Specifies whether or not verbose messages are displayed.

cb, irb_change_binding[obj]
Creates and enters a new binding that has its own scope for local variables. If objis given, it will be used as self in the new binding.

irb[obj]
Starts an irb subsession. If objis given, it will be used as self.

jobs, irb_jobs
Lists irb subsessions.

fg n, irb_fg n
Switches into the specified irb subsession. n may be any of the following values:

irb subsession number
thread id
irb object
self (theobjthat launched a particular subsession)

kill n, irb_kill n
Kills an irb subsession. n may be any of the values as described for irb_fg.

Configuring the Prompt

You have a lot of flexibility in configuring the prompts that irb uses. Sets of prompts are stored in the prompt hash:

IRB.conf[:PROMPT]

For example, to establish a new prompt mode called ``MY_PROMPT'', you might enter the following (either directly at an irb prompt or in the .irbrcfile):

IRB.conf[:PROMPT][:MY_PROMPT] = { # name of prompt mode :PROMPT_I => "...", # normal prompt :PROMPT_S => "...", # prompt for continuing strings :PROMPT_C => "...", # prompt for continuing statement :RETURN => " ==>%s\n" # format to return value }

Then, invoke irb with the prompt mode above by

% irb --prompt my-prompt

Or set the following configuration value:

IRB.conf[:PROMPT_MODE] = :MY_PROMPT

The constants PROMPT_I, PROMPT_S, and PROMPT_Cspecify the format for each of the prompt strings. Within the prompt format, the following flags are available and will expand to the given text:

Flag Description
%N Current command.
%m to_sof the main object (self).
%M inspectof the main object (self).
%l Delimiter type. In strings that are continued across a line break,%lwill display the type of delimiter used to begin the string, so you'll know how to end it. The delimiter will be one of",',/,], or`.
%ni Indent level. The optional number n is used as a width specification to printf, asprintf("%nd").
%nn Current line number (n used as with the indent level).
%% A literal percent sign.

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" }

Restrictions

Because of the way irb works, there is a minor incompatibility between it and the standard Ruby interpreter. The problem lies in the determination of local variables.

Normally, Ruby looks for an assignment statement to determine if something is a variable---if a name hasn't been assigned to, then Ruby assumes that name is a method call.

eval "a = 0" a
produces:
prog.rb:2: undefined local variable or method `a'
for # (NameError)

In this case, the assignment is there, but it's within a string, so Ruby doesn't take it into account.

irb, on the other hand, executes statements as they are entered.

irb(main):001:0> eval "a = 0" 0 irb(main):002:0> a 0

In irb, the assignment was executed before the second line was encountered, so ``a'' is correctly identified as a local variable.

If you need to match the Ruby behavior more closely, you can place these statements within a begin/ endpair.

irb(main):001:0> begin irb(main):002:1* eval "a = 0" irb(main):003:1> a irb(main):004:1> end NameError: undefined local variable or method `a' (irb):3:in `irb_binding'

rtags, xmp, and the Frame Class

The base version of irb is installed along with Ruby itself. But there is an extended version of irb in the archives containing a few extra goodies that need mentioning.

rtags

rtagsis a command used to create a TAGSfile for use with either the emacs or vi editor.

rtags[-vi][files]...

By default, rtags makes a TAGSfile suitable for emacs (see etags.el). The -vioption makes a TAGS file for use with vi.

rtags needs to be installed in the same manner as irb (that is, you need to install irb in the library path and make a link from irb/rtags.rbto bin/rtags).

xmp

irb's xmp is an ``example printer''---that is, a pretty-printer that shows the value of each expression as it is run (much like the script we wrote to format the examples in this book). There is also another stand-alone xmp in the archives.

xmp can be used as follows:

require "irb/xmp"

xmp <
produces:
[pwd:/tc/work/ruby/ProgrammingRuby/latex] artist = "Doc Severinsen" ==>"Doc Severinsen" artist ==>"Doc Severinsen"

Or, it can be used as an object instance. Used in this fashion, the object maintains context between invocations:

require "irb/xmp"

x = XMP.new x.puts <

x.puts <
produces:
[pwd:/tc/work/ruby/ProgrammingRuby/latex] artist = "Louis Prima" ==>"Louis Prima" artist ==>"Louis Prima"

You can explicitly provide a binding with either form; otherwise, xmp uses the caller's environment.

xmp code_string, abinding XMP.new(abinding)

Note that xmp does not work with multithreading.

The Frame Class

The IRB::Frameclass represents the interpreter's stack and allows easy access to the Bindingenvironment in effect at different stack levels.

IRB::Frame.top(n = 0) Returns aBindingfor the nth context from the top. The 0th context is topmost, most recent frame.
IRB::Frame.bottom(n = 0) Returns aBindingfor the nth context from the bottom. The 0th context is the bottommost, initial frame.
IRB::Frame.sender Returns the object (the sender) that invoked the current method.

You can use this facility, for instance, to examine local variables from the method that called the current method:

require 'irb/frame'

def outie b = IRB::Frame.top(1) eval "p my_local", b end

def innie my_local = 102.7 outie end

innie
produces:
102.7

Note that this doesn't work with multithreaded programs.


Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
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