From 39398372c96c1c4f23febf562eab35e232573ece Mon Sep 17 00:00:00 2001 From: Alain Reguera Delgado Date: Oct 06 2013 04:14:40 +0000 Subject: Add article named "Understanding Modules". - It in the very first stage of elaboration so don't relay much in it yet. --- diff --git a/Automation/Manuals/Understanding_Modules/render.conf b/Automation/Manuals/Understanding_Modules/render.conf new file mode 100644 index 0000000..e705483 --- /dev/null +++ b/Automation/Manuals/Understanding_Modules/render.conf @@ -0,0 +1,9 @@ +[understanding_modules.html] +render-type = "asciidoc" +render-flow = "article" +render-from = "understanding_modules.asciidoc" +locale-from = "${TCAR_SCRIPT_LANG_LC}/messages.po" +images-from = "${TCAR_BASEDIR}/Artworks/Icons/Webenv" +styles-from = "${TCAR_BASEDIR}/Artworks/Webenv/Docbook/1.69.1/Css" +formats = "xhtml" +render-page = "single chunks" diff --git a/Automation/Manuals/Understanding_Modules/understanding_modules.asciidoc b/Automation/Manuals/Understanding_Modules/understanding_modules.asciidoc new file mode 100644 index 0000000..a5b863b --- /dev/null +++ b/Automation/Manuals/Understanding_Modules/understanding_modules.asciidoc @@ -0,0 +1,414 @@ +Understanding Modules +===================== +Alain Reguera Delgado +v1.0, Oct 2013 + +Introduction +------------ + +From version 0.5 of The CentOS Artwork Repository on, the +*centos-art.sh* script was redesigned to introduce the idea of modules +to its base design. Modules are a collection of functions written in +Bash that can call one another to create individual execution +environments. They may be nested efficiently to achieve high levels of +maintainability and extensibility. This make possible for modules +writers to divide complicated tasks into smaller tasks that can be +easier to debug, maintain and share with other modules efficiently +(e.g., instead of loading modules all at once, they are only loaded at +demand and unset once they conclude their execution). + +Inside the *centos-art.sh* script there are two kinds of functions, +which are: "global functions" and "module-specific functions." The +global functions are defined in the very beginning of *centos-art.sh* +script and remain in memory for you to call whenever you need it using +a regular function call syntax. The module-specific functions, on the +other hand, are defined at demand for specific tasks and removed from +memory once the task they were created for is over. The collection of +all module-specific functions related to the same task is what we call +a module environment. Module environments can be either top-module, +sub-module or sib-module and all are executed through the +*tcar_setModuleEnvironment* global function. + +This article describes the modular design of *centos-art.sh* script. +It is a good place to start if you are planning to contribute new +module environments to *centos-art.sh* script. The next section +delves into what a module environment is, the tree module types you +can find and the correct way of execute them. + +The Module Environment +---------------------- + +The module environment provides an array of strings (called the +environment). You can use this environment to deploy solutions for +specific problems. Inside the *centos-art.sh* script, module +environments are made of small functions that create small +environments to solve small problems. Then they are combined in a +specific order to solve bigger problems. The process of initiating a +module environment inside *centos-art.sh* script starts at the end of +the *centos-art.sh* file itself, with the invocation of the +*tcar_setModuleEnvironment* function. This function, at this point, +executes the module environment for the module name you specified in +the first argument of the command-line. The modules you specified in +the command-line are also known as top-modules. + +Top-modules initiate the higher module environment inside +*centos-art.sh* script. This means that variables and functions +defined inside it will be available as long as its execution-time +last. Top-modules are stored directly inside the +Modules/+ directory +of *centos-art.sh* script, as described in <>. +Top-modules use to be small and have well defined goals. Top-modules +exist to define global variables for task-specific actions, interpret +module-specific options passed through the command-line and execute +the appropriate actions based on them. These actions can be involve +calling other top-modules or sub-modules. + +Sub-modules are also module environments. They are executed by the +*tcar_setModuleEnvironment* function when the *-t sub-module* option +is passed to it. Sub-modules have the characteristic of being nested +modules. They are generally executed one inside another to create a +chain of module environments. A chain of module environments is very +useful in situations where you want to divide one large task into +smaller tasks and also control which of those smaller tasks are loaded +based on specific conditions (e.g., you want to render both images and +documentation). In a chain of modules, module environments at a lower +level in the chain (those started last) have access to higher module +environments (those started first), but not the opposite. When +processing information this way, module environments aren't destroyed +until the last module environment loaded is done. At that point, +module environments are destroyed in the reverse order they were +loaded (e.g., if the chain of module was executed as +``render->images->svg'', then, when ``svg'' module environment is +done, the chain of modules will be destroy ``images'' and finally +``render''). + +Module environments can also share one common module environment on +top of them to create sibling processing (sib-module). Sibling +processing is very useful in situations where you start processing +information in a way and then need to jump to another related but +different kind of processing (e.g., when you are rendering +documentation you first start rendering it as html and then jump into +manpage). In this situation, you open a module environment that +contains information useful for two or more different but related kind +of processing and jump from one to another without destroying the +common information. However, when one of the specific ways of +processing information is done, it is destroyed. This, before opening +a new way of processing (e.g., once html processing is done, the html +module is destroyed and, then, the manpage module is loaded). So, +only the required modules are active while processing information. + +When we say that a module environment is destroyed it means that all +the related variables and functions which make that module environment +useful are removed from *centos-art.sh* script execution environment, +which make the module environment inoperable to all effects, indeed. +However, it is worth to know that all global array variables the +*tcar_setModuleEnvironment* function uses to store module-specific +information remain active until the last module environment is +destroyed (i.e., the top-module executed from the command-line). This +make possible for *centos-art.sh* script to ``remember'' information +about all different but related module environments loaded to perform +specific tasks. Such remembering feature is what make possible to +implement sib-modules as described above. + +[[module-implementation]] +Module Implementation +--------------------- + +The implementation of module environments take place in two locations. +The first location is the module directory structure and the second +location *tcar_setModuleEnvironment* function. The module directory +structure contains a standard distribution of files and directories +that the *tcar_setModuleEnvironment* function recognizes and uses for +executing functions inside it. Each module environment you want to +execute needs a module directory in the *centos-art.sh* script tree. +In this directory you organize the functions that make your module +environment useful. The directory structure of your module directory +is important because *tcar_setModuleEnvironment* makes use of it to +know module-specific information. + +The *tcar_setModuleEnvironment* function is stored in the +Scripts/+ +directory. It uses global array variables to store information about +the modules and (non-array) local variables to handle the information +stored about modules in each call of the function. Each time you call +the *tcar_setModuleEnvironment* function, it increments the array +variables counter, stores module-specific information in the array +variables, reset (non-array) local variables using the current +module's information stored in the array variables and executes the +module's initialization script from (non-array) local variables. When +the module's environment finishes its execution, the array counter +decrements and the module's environment is destroyed, to free the +memory it was using. This process repeats continually, each time you +call the *tcar_setModuleEnvironment* function. + +[TIP] +====================================================================== +In case you want to see how modules are created and destroyed inside, +pass the *--debug* option to *centos-art.sh* script. It will activate +the script internal debugger for you to see the whole process. +====================================================================== + +To illustrate how modules need to be implemented inside +*centos-art.sh* script in order for *tcar_setModuleEnvironment* to +execute them correctly, we'll use a module named ``hello'' as example +in the next sections to describe the steps you need to follow for +creating new modules from scratch. The purpose of *hello* module is +to print out greetings to standard output and exit successfully. See +*hello(1)*, for more information about it. + +Planning New Module +------------------- + +Planning is probably the first thing you need to do in order to create +a new module to *centos-art.sh* script. It would be very helpful if +you read documentation and bugs related to modules and function in +order to find out possible tasks you might take as motivation for your +contributions. Such investigation always help. + +The motivation behind the *hello* module came with the need of having +a simple module that could be used as reference to describe how to +create and execute new modules inside *centos-art.sh* script. The top +modules we have by now aren't suitable for a simple description about +how to create new modules from scratch. Instead, I thought that +creating a simple module for that purpose would be better. Suddenly, I +recalled the GNU's hello package which describes their standards about +well written GNU packages and found motivation enough to create a +*hello* module under the same idea but this time focused on +*centos-art.sh* script, instead. + +The motivation for planning your own modules might vary. No matter +what it would be, use it with confidence, plan your module, set the +final spot where you want to get to and then, read the next section. +It describes the steps you need to follow in order to write a +functional module inside *centos-art.sh* script. + +Creating New Module +------------------- + +The <>, shows a basic module structure. In this +example, we see that module directories are written capitalized while +module initialization file and related functions are all written in +lower-case. Note also how the module directory and files inside it use +the module's name in their file names to get identified. This is a +convention that should be followed in order for *centos-art.sh* script +to execute modules. Another convention you should follow, when +creating related functions, is using underscore (``_'') to separate +the module's name from the function's descriptive name. In these +cases, the function's descriptive name is always written in camel-case +followed by the +.sh+ extension. + +[[directory-structure]] +.The directory structure +====================================================================== +---------------------------------------------------------------------- +. +|-- COPYING <-- Contains the GPL license. +|-- Locales/ <-- localization of all sh files. +|-- Manuals/ <-- manuals for main and global functions. +|-- Modules/ <-- top-modules are stored here. +| `-- Hello/ <-- top-module directory. +| `-- hello.sh <-- top-module initialization file. +|-- Scripts/ <-- global functions are stored here. +|-- centos-art.conf.sh <-- main configuration file. +`-- centos-art.sh <-- main initialization file. +---------------------------------------------------------------------- +====================================================================== + +[[directory-structure-extended]] +.The directory structure with extended functionality +====================================================================== +---------------------------------------------------------------------- +. +|-- COPYING +|-- Locales/ +|-- Manuals/ +|-- Modules/ +| `-- Hello/ +| |-- Modules/ <-- Hello sub-modules are stored here. +| | |-- Actions/ <-- Sub-module of Hello but sib-module of Lowercase and Uppercase +| | | `-- actions.sh <-- sub-module initialization file. +| | |-- Lowercase/ <-- Sub-module of Hello but sib-module of Actions and Uppercase. +| | | `-- lowercase.sh +| | `-- Uppercase/ <-- Sub-module of Hello but sib-module of Actions and Lowercase. +| | `-- uppercase.sh +| `-- hello.sh +|-- Scripts/ +|-- centos-art.conf.sh +`-- centos-art.sh +---------------------------------------------------------------------- +====================================================================== + +The module's initialization file contains the main function definition +of your module. It is a good place to define variables that must be +always available inside the module. There is also a top-comment that +collects information about the function files you are writing (e.g., a +small description, a written by section, the copyright note and the +legal status of the file). Even using a top comment like this is not +required for *centos-art.sh* script to execute modules properly, it is +very useful as matter of consistency and style inside it (and the +copyright and legal notice might be required for legal protection of +your code as set by GPL). Finally, there is the function definition +named +hello+ just as the directory that holds it but all in lowercase. +Inside this function definition is where we write what we want the +*hello* module does for us. This way, following with the *hello* example, +we create an array variable inside it holding all the suggestions we +would like to print, as described in <>. + +[[initialization-file]] +.The initialization file of hello module +====================================================================== +---------------------------------------------------------------------- +#!/bin/bash +###################################################################### +# +# hello.sh -- Print out greetings to standard output and exit +# successfully. +# +# Written by: +# * Alain Reguera Delgado , 2013 +# +# Copyright (C) 2009-2013 The CentOS Artwork SIG +# +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 2 of the License, or (at +# your option) any later version. +# +# This program is distributed in the hope that it will be useful, but +# WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +# General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program; if not, write to the Free Software +# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. +# +###################################################################### + +function hello { + + tcar_printMessage "Hello, World!" + +} +---------------------------------------------------------------------- +====================================================================== + +You can nest modules by creating directory structures like this, +inside the Modules/ directory of the higher module you want to extend +its functionality. + +Inside the repository, modules related to *centos-art.sh* script are +stored in the directory +Automation/Modules/${MODULE_NAME}/+. + +*Modules/*:: + This directory contains module's modules. +*Manuals/*:: + This directory contains module's documentation produced by *help* + module. The structure of this directory looks as follow: ++ +---------------------------------------------------------------------- +Manuals/ +|-- ${LANG}/ +| |-- man${SECTION_NUMBER} +| `-- ${MODULE_NAME}.${SECTION_NUMBER} +`-- man${SECTION_NUMBER} + `-- ${MODULE_NAME}.${SECTION_NUMBER} +---------------------------------------------------------------------- + +*Locales/*:: + This directory contains module's translations produced by *locale* + module. The structure of this directory looks as follow: ++ +---------------------------------------------------------------------- +Locales/ +`-- ${LANG}/ + |-- LC_MESSAGES + | |-- ${MODULE_NAME}.sh.mo + | `-- ${MODULE_NAME}.docbook.mo + |-- ${MODULE_NAME}.sh.po + |-- ${MODULE_NAME}.sh.pot + |-- ${MODULE_NAME}.docbook.po + `-- ${MODULE_NAME}.docbook.pot +---------------------------------------------------------------------- + +*Scripts/*:: + This directory contains function scripts written by module's + writers. Here is where all the tasks the module is useful for are + written and stored in. As convention the following structure is + used: ++ +---------------------------------------------------------------------- +Scripts/ +`-- ${MODULE_NAME}_${FUNCTION_NAME}.sh +---------------------------------------------------------------------- ++ +{asccidoc-br} ++ +Inside each function script, there is a top comment where you should +put the name of the function script, a brief description about what it +does, as well as author and copying information. After the top comment +and separated by one white line, you should define the function +sentence using the long format. ++ +---------------------------------------------------------------------- +#!/bin/bash +###################################################################### +# +# ${MODULE_NAME}_${FUNCTION_NAME}.sh -- ${FUNCTION_DESCRIPTION} +# +# Written by: +# * ${AUTHOR_NAME} <${AUTHOR_EMAIL}>, ${YEARS} +# +# Copyright (C) ${YEAR} The CentOS Artwork SIG +# +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 2 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, but +# WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +# General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program; if not, write to the Free Software +# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. +# +###################################################################### + +function ${MODULE_NAME}_${FUNCTION_NAME} { + ... +} +---------------------------------------------------------------------- ++ +[NOTE] +If your are planning to contribute a new module to *centos-art.sh* +script, please, consider using the layout described above for all your +function scripts, consistently. + +*$\{MODULE_NAME}.asciidoc*:: + This file contains the module's documentation source. From this + file it is possible to produce the same documentation in other + formats including manpage, html and pdf. Whenever you need to + improve the module's documentation, edit this file. +*$\{MODULE_NAME}.conf*:: + This file contains the module's configuration variables. These + variables are exported to the environment and remain there as long + as the script execution environment is alive. Some variables are + read-only others not. ++ +The configuration file provides explanation about each environment +variable it exports. If you want to know more about what these +variables are, open this file and read the comments near each +variable. + +*$\{MODULE_NAME}.sh*:: + This is the module's initialization script. The first file + executed when the module called from the command-line. This file + provides access to argument parsing and controls how + module-specific function scripts are called. This is the starting + point for writing modules. You can write a complete module using + this file only but, frequently, it is convenient as the module + complexity grows to divide it in smaller pieces (function scripts) + to improve maintainability and error findings. + +// vim: set syntax=asciidoc: