Understanding Modules ===================== Alain Reguera Delgado v0.1, Oct 2013 Overview -------- From version 0.5, the *centos-art.sh* script introduces 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 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). This article describes the modular design of *centos-art.sh* script. It is a good place for you to start if you are planning to contribute new module environments to *centos-art.sh* script or want to know more about how it works. The next section delves into what a module environment is, the three module types you can find in it and the correct way of execute each one of them. [[module-environment]] Module Environment ------------------ When you execute the *centos-art.sh* script you create an execution environment in which variables and functions are defined. The execution environment is the higher environment inside *centos-art.sh* script it is considered to have a ``global'' scope, so variables and functions defined in it are always available for any function execution made from it. You can control this execution environment through the files +centos-art.sh+ and +centos-art.conf.sh+. These files don't provide too much functionality so module environments are executed inside it to extend its functionality. Module environments are made of small functions that perform small tasks and can be further executed in a specific order to create the desired result. Module environments are executed and destroyed at demand. Inside *centos-art.sh*, module environments can be either ``parent modules,'' ``child modules,'' or ``sibling modules.'' Parent Modules ~~~~~~~~~~~~~~ Parent modules are initiated by executing the *tcar_setModuleEnvironment* function with the *-t parent* option set on it. Parent modules are very simple in design and you can use them to implement simple solutions quickly. Normally, when you execute a parent module, you initiate the highest module environment possible inside *centos-art.sh* script. Because of such high scope, parent modules are frequently used to define module's global variables, interpret module-specific options passed through the command-line and execute the appropriate actions based on them. In <>, we have executed the *hello* module with the *--greeting=hi* and *--debug* options through the command-line. In this example, *centos-art.sh* script executes a parent module named *hello*, processes the module-specific options passed through the command-line, prints a greeting message to standard output and exits successfully. [[debug-parent-modules]] .Debugging execution of parent modules ====================================================================== ---------------------------------------------------------------------- Thu 10 Oct 2013 11:53:28 PM CDT =========================> [0] | main Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_BASEDIR Automation/Modules Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_NAME [0]=hello Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_TYPE parent Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_ARGUMENT --greeting=hi Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_LIST hello|help|locale|prepare|render|tuneup|vcs Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Manuals Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Configs Thu 10 Oct 2013 11:53:28 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/hello.sh Thu 10 Oct 2013 11:53:28 PM CDT TEXTDOMAIN hello.sh Thu 10 Oct 2013 11:53:28 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:53:28 PM CDT export -f hello Thu 10 Oct 2013 11:53:28 PM CDT export -f hello_getOptions Thu 10 Oct 2013 11:53:28 PM CDT -------------------------> hello --greeting=hi hi Thu 10 Oct 2013 11:53:28 PM CDT <------------------------- hello Thu 10 Oct 2013 11:53:28 PM CDT unset -f hello Thu 10 Oct 2013 11:53:28 PM CDT unset -f hello_getOptions Thu 10 Oct 2013 11:53:28 PM CDT <========================= [0] | main ---------------------------------------------------------------------- ====================================================================== <> describes an entire module environment in action. With this information you can create your own module environment, already. However, when your module is getting too much complicated you probably want to divide it in smaller pieces that you can execute accordingly, based on the purpose you defined for it. Such kind of division can be implemented through ``modules' related functions.'' Module's related functions are stored in the same directory of your module's initialization file and they are very useful when you are refactoring it. Definitions of module's related functions are loaded before the initialization file does, so it is a good practice to create them only when you are absolutely sure they will be executed in your module. Otherwise they may be loaded and never be used, which make the script to waste memory unnecessarily. In these cases, when you need to divide the logic of a module in smaller pieces where these pieces may or may not be executed based on specific conditions, all taking place in the same interaction, then using ``_child modules_'' is a more suitable approach. [[child-modules]] Child Modules ~~~~~~~~~~~~~ Child modules are initiated by executing the *tcar_setModuleEnvironment* function with the *-t child* option set on it. Child modules have the characteristic of being nested modules. They cannot be executed from the command-line. Normally, child modules are executed from parent modules but they can be executed from other child modules, too. When several child modules are executed in one single interaction of *centos-art.sh*, they create a chain of modules. A chain of modules is very useful in situations where you want to divide one large task into smaller tasks and also control which of these smaller tasks is executed based on specific conditions (e.g., you may want to render images or documentation, but not both, in one single interaction of *centos-art.sh* script). In a chain of modules, lower modules in the chain (those started last) have access to information set by modules higher in the chain (those started first), but not the opposite. When processing information this way, modules aren't destroyed until the last module executed in the chain has finished its work (e.g., all the commands inside it have been executed). At that point, child modules are destroyed in the reverse order they were executed. For example, when you execute the *hello* module with both *--debug* and *--upper* option, *centos-art.sh* script creates a chain of three modules to produce the greeting message. Firstly, it begins by executing the parent module named *hello*, then it continues with the child module named *output* which in turn executes the child module name *lower* to finally print the expected greeting message. In this example, the module named *lower* is the last module in the chain of executed modules. It has access to all information defined by earlier modules (e.g., in *hello* and *output* modules) and none of its earlier modules will be destroyed until it has finished its work. This process becomes more visible when you take a look at <>. [[debug-child-modules]] .Debugging execution of child modules ====================================================================== ---------------------------------------------------------------------- Thu 10 Oct 2013 11:52:41 PM CDT =========================> [0] | main Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_BASEDIR Automation/Modules Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_NAME [0]=hello Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_TYPE parent Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_ARGUMENT --upper --greeting=hi Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_LIST hello|help|locale|prepare|render|tuneup|vcs Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Manuals Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Configs Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/hello.sh Thu 10 Oct 2013 11:52:41 PM CDT TEXTDOMAIN hello.sh Thu 10 Oct 2013 11:52:41 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:52:41 PM CDT export -f hello Thu 10 Oct 2013 11:52:41 PM CDT export -f hello_getOptions Thu 10 Oct 2013 11:52:41 PM CDT -------------------------> hello --upper --greeting=hi Thu 10 Oct 2013 11:52:41 PM CDT =========================> [1] | hello Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_NAME [1]=output Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_TYPE child Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_LIST output Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Manuals Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Locales Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Configs Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/output.sh Thu 10 Oct 2013 11:52:41 PM CDT TEXTDOMAIN output.sh Thu 10 Oct 2013 11:52:41 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Locales Thu 10 Oct 2013 11:52:41 PM CDT export -f output Thu 10 Oct 2013 11:52:41 PM CDT -------------------------> output Thu 10 Oct 2013 11:52:41 PM CDT =========================> [2] | output Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_NAME [2]=upper Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_TYPE child Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_LIST camel|lower|random|upper Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output/Modules/Upper Thu 10 Oct 2013 11:52:41 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules/Upper/Modules Thu 10 Oct 2013 11:52:42 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Modules/Upper/Manuals Thu 10 Oct 2013 11:52:42 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Modules/Upper/Locales Thu 10 Oct 2013 11:52:42 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Modules/Upper/Configs Thu 10 Oct 2013 11:52:42 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/Modules/Upper/upper.sh Thu 10 Oct 2013 11:52:42 PM CDT TEXTDOMAIN upper.sh Thu 10 Oct 2013 11:52:42 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Modules/Upper/Locales Thu 10 Oct 2013 11:52:42 PM CDT export -f upper Thu 10 Oct 2013 11:52:42 PM CDT -------------------------> upper HI Thu 10 Oct 2013 11:52:42 PM CDT <------------------------- upper Thu 10 Oct 2013 11:52:42 PM CDT unset -f upper Thu 10 Oct 2013 11:52:42 PM CDT <========================= [2] | output Thu 10 Oct 2013 11:52:42 PM CDT <------------------------- output Thu 10 Oct 2013 11:52:42 PM CDT unset -f output Thu 10 Oct 2013 11:52:42 PM CDT <========================= [1] | hello Thu 10 Oct 2013 11:52:42 PM CDT <------------------------- hello Thu 10 Oct 2013 11:52:42 PM CDT unset -f hello Thu 10 Oct 2013 11:52:42 PM CDT unset -f hello_getOptions Thu 10 Oct 2013 11:52:42 PM CDT <========================= [0] | main ---------------------------------------------------------------------- ====================================================================== The module environment described in <> shows the child modules' ability of reducing scope as they get deeper in the chain of executed modules. However, child modules lack the possibility of nest modules that share the same scope. For example, in the *hello* module described above, you cannot execute the modules *lower* or *upper* from *camel* module, as if they were child modules of it. That is not possible because they all have the same scope, which is, to print the greeting message to standard output. Child modules are conceived to reduce the module scope as new child modules are executed. When you need to execute new module environments and, also, retain the last scope from which the new module is executed, you need to use ``_sibling modules_,'' instead. Sibling Modules ~~~~~~~~~~~~~~~ Sibling modules are initiated by executing the *tcar_setModuleEnvironment* function with the *-t sibling* option set on it. Sibling modules are another type of nested modules but, in contrast with child modules, sibling modules cannot be executed from parent modules. Normally, sibling modules are executed from other sibling modules but, considering the context, they can be executed from child module too, to initiate sibling processing. When several siblings modules are executed, they also build a chain of modules. In contrast with the chain of child modules, the chain of sibling modules destroys the last sibling module executed before executing the next sibling module. This make the chain to stop its growing at sibling module processing, unless you call a child module from a sibling module. In this case, the chain expansion would continue as long as the number of child modules you execute. This process becomes more visible when you take a look at <>. In <>, we've executed the *hello* module with the *--greeting=hi*, *--camel*, and *--debug* options. In this example, *centos-art.sh* script executes the *hello* module then the *output* module which in turn executes the *camel* module. At this point, can appreciate how the chain of modules stop growing. Observe that *camel* module has gained the position 2 in the chain of modules and executes the *upper* module which takes the position 3, as expected. Now, when *upper* module finishes its work it is destroyed and the module's counter is reset to its previous value which is 2 (the one set by *camel* module). Then, *camel* executes the *lower* module which take position 3 at the chain of modules until it finishes. When it finishes, the *camel* module finishes its work and is destroyed, then *output*, then *hello*. [[debug-sibling-modules]] .Debugging execution of sibling modules ====================================================================== ---------------------------------------------------------------------- Thu 10 Oct 2013 11:51:42 PM CDT =========================> [0] | main Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_BASEDIR Automation/Modules Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_NAME [0]=hello Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_TYPE parent Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_ARGUMENT --camel --greeting=hi Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_LIST hello|help|locale|prepare|render|tuneup|vcs Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Manuals Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Configs Thu 10 Oct 2013 11:51:42 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/hello.sh Thu 10 Oct 2013 11:51:42 PM CDT TEXTDOMAIN hello.sh Thu 10 Oct 2013 11:51:42 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:51:43 PM CDT export -f hello Thu 10 Oct 2013 11:51:43 PM CDT export -f hello_getOptions Thu 10 Oct 2013 11:51:43 PM CDT -------------------------> hello --camel --greeting=hi Thu 10 Oct 2013 11:51:43 PM CDT =========================> [1] | hello Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_NAME [1]=output Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_TYPE child Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_LIST output Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Manuals Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Locales Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Configs Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/output.sh Thu 10 Oct 2013 11:51:43 PM CDT TEXTDOMAIN output.sh Thu 10 Oct 2013 11:51:43 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Locales Thu 10 Oct 2013 11:51:43 PM CDT export -f output Thu 10 Oct 2013 11:51:43 PM CDT -------------------------> output Thu 10 Oct 2013 11:51:43 PM CDT =========================> [2] | output Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_NAME [2]=camel Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_TYPE child Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_LIST camel|lower|random|upper Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output/Modules/Camel Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules/Camel/Modules Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Modules/Camel/Manuals Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Modules/Camel/Locales Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Modules/Camel/Configs Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/Modules/Camel/camel.sh Thu 10 Oct 2013 11:51:43 PM CDT TEXTDOMAIN camel.sh Thu 10 Oct 2013 11:51:43 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Modules/Camel/Locales Thu 10 Oct 2013 11:51:43 PM CDT export -f camel Thu 10 Oct 2013 11:51:43 PM CDT -------------------------> camel Thu 10 Oct 2013 11:51:43 PM CDT =========================> [3] | camel Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_NAME [3]=upper Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_TYPE sibling Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_LIST camel|lower|random|upper Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output/Modules/Upper Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules/Upper/Modules Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Modules/Upper/Manuals Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Modules/Upper/Locales Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Modules/Upper/Configs Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/Modules/Upper/upper.sh Thu 10 Oct 2013 11:51:43 PM CDT TEXTDOMAIN upper.sh Thu 10 Oct 2013 11:51:43 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Modules/Upper/Locales Thu 10 Oct 2013 11:51:43 PM CDT export -f upper Thu 10 Oct 2013 11:51:43 PM CDT -------------------------> upper H Thu 10 Oct 2013 11:51:43 PM CDT <------------------------- upper Thu 10 Oct 2013 11:51:43 PM CDT unset -f upper Thu 10 Oct 2013 11:51:43 PM CDT <========================= [3] | camel Thu 10 Oct 2013 11:51:43 PM CDT =========================> [3] | camel Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_NAME [3]=lower Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_TYPE sibling Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_LIST camel|lower|random|upper Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output/Modules/Lower Thu 10 Oct 2013 11:51:43 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules/Lower/Modules Thu 10 Oct 2013 11:51:44 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Modules/Lower/Manuals Thu 10 Oct 2013 11:51:44 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Modules/Lower/Locales Thu 10 Oct 2013 11:51:44 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Modules/Lower/Configs Thu 10 Oct 2013 11:51:44 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/Modules/Lower/lower.sh Thu 10 Oct 2013 11:51:44 PM CDT TEXTDOMAIN lower.sh Thu 10 Oct 2013 11:51:44 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Modules/Lower/Locales Thu 10 Oct 2013 11:51:44 PM CDT export -f lower Thu 10 Oct 2013 11:51:44 PM CDT -------------------------> lower i Thu 10 Oct 2013 11:51:44 PM CDT <------------------------- lower Thu 10 Oct 2013 11:51:44 PM CDT unset -f lower Thu 10 Oct 2013 11:51:44 PM CDT <========================= [3] | camel Thu 10 Oct 2013 11:51:44 PM CDT <------------------------- camel Thu 10 Oct 2013 11:51:44 PM CDT unset -f camel Thu 10 Oct 2013 11:51:44 PM CDT <========================= [2] | output Thu 10 Oct 2013 11:51:44 PM CDT <------------------------- output Thu 10 Oct 2013 11:51:44 PM CDT unset -f output Thu 10 Oct 2013 11:51:44 PM CDT <========================= [1] | hello Thu 10 Oct 2013 11:51:44 PM CDT <------------------------- hello Thu 10 Oct 2013 11:51:44 PM CDT unset -f hello Thu 10 Oct 2013 11:51:44 PM CDT unset -f hello_getOptions Thu 10 Oct 2013 11:51:44 PM CDT <========================= [0] | main ---------------------------------------------------------------------- ====================================================================== <> shows a single interaction of *centos-art.sh* script executing different types of modules. Normally, one module is executed at some point and destroyed at the same point when it has finished its work, however, what if the next immediate module you are about to execute is the same module you are about to destroyed? This is, you need to execute the last module in the chain of executed modules again, but, this time, from itself. In cases like this, the *centos-art.sh* script doesn't destroy the last module. It cannot, because you are certainly executing a new module from itself, so it has to wait for this new call to finish in order to be destroyed. This kind of processing is known as _processing modules recursively._ Recursive Modules ~~~~~~~~~~~~~~~~~ When one module environment executes itself we are in presence of a recursive module execution. The execution of modules recursively doesn't destroy the last module in the chain of executed modules and doesn't increment or decrement the module counter either. The module counter is somehow frozen until a different module environment is executed. In this cases, the last module environment remains in memory for the new module execution to make use of. This process becomes more visible when you take a look at <>. [CAUTION] When you execute modules recursively, you should be very careful not to get trapped into an endless loop. In <>, we've executed the *hello* module with the *--greeting=hello*, *--random*, and *--debug* options. In this example, *centos-art.sh* script executes a parent module named *hello* which in turn executes a child module named *output* which in turn executes a child module named *random*. At this point, the *random* modules executes itself five times (the number of characters passed as value to greeting option) to print out random letters from the greeting message. The output may have no much sense on itself but the related debugging information helps to understand the execution of modules recursively. [[debug-recursive-modules]] .Processing execution of modules recursively ====================================================================== ---------------------------------------------------------------------- Thu 10 Oct 2013 11:50:03 PM CDT =========================> [0] | main Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_BASEDIR Automation/Modules Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_NAME [0]=hello Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_TYPE parent Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_ARGUMENT --random --greeting=Hello Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_LIST hello|help|locale|prepare|render|tuneup|vcs Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules Thu 10 Oct 2013 11:50:03 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Manuals Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Configs Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/hello.sh Thu 10 Oct 2013 11:50:04 PM CDT TEXTDOMAIN hello.sh Thu 10 Oct 2013 11:50:04 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Locales Thu 10 Oct 2013 11:50:04 PM CDT export -f hello Thu 10 Oct 2013 11:50:04 PM CDT export -f hello_getOptions Thu 10 Oct 2013 11:50:04 PM CDT -------------------------> hello --random --greeting=Hello Thu 10 Oct 2013 11:50:04 PM CDT =========================> [1] | hello Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_NAME [1]=output Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_TYPE child Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_LIST output Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Manuals Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Locales Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Configs Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/output.sh Thu 10 Oct 2013 11:50:04 PM CDT TEXTDOMAIN output.sh Thu 10 Oct 2013 11:50:04 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Locales Thu 10 Oct 2013 11:50:04 PM CDT export -f output Thu 10 Oct 2013 11:50:04 PM CDT -------------------------> output Thu 10 Oct 2013 11:50:04 PM CDT =========================> [2] | output Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_BASEDIR Automation/Modules/Hello/Modules/Output/Modules Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_NAME [2]=random Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_TYPE child Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_ARGUMENT Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_LIST camel|lower|random|upper Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR Automation/Modules/Hello/Modules/Output/Modules/Random Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_MODULES Automation/Modules/Hello/Modules/Output/Modules/Random/Modules Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_MANUALS Automation/Modules/Hello/Modules/Output/Modules/Random/Manuals Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_LOCALES Automation/Modules/Hello/Modules/Output/Modules/Random/Locales Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_DIR_CONFIGS Automation/Modules/Hello/Modules/Output/Modules/Random/Configs Thu 10 Oct 2013 11:50:04 PM CDT TCAR_MODULE_INIT_FILE Automation/Modules/Hello/Modules/Output/Modules/Random/random.sh Thu 10 Oct 2013 11:50:04 PM CDT TEXTDOMAIN random.sh Thu 10 Oct 2013 11:50:04 PM CDT TEXTDOMAINDIR Automation/Modules/Hello/Modules/Output/Modules/Random/Locales Thu 10 Oct 2013 11:50:04 PM CDT export -f random Thu 10 Oct 2013 11:50:04 PM CDT -------------------------> random H Thu 10 Oct 2013 11:50:04 PM CDT ~~~~~~~~~~~~~~~~~~~~~~~~~> random H Thu 10 Oct 2013 11:50:04 PM CDT ~~~~~~~~~~~~~~~~~~~~~~~~~> random l Thu 10 Oct 2013 11:50:04 PM CDT ~~~~~~~~~~~~~~~~~~~~~~~~~> random l Thu 10 Oct 2013 11:50:04 PM CDT ~~~~~~~~~~~~~~~~~~~~~~~~~> random H Thu 10 Oct 2013 11:50:04 PM CDT <------------------------- random Thu 10 Oct 2013 11:50:04 PM CDT unset -f random Thu 10 Oct 2013 11:50:04 PM CDT <========================= [2] | output Thu 10 Oct 2013 11:50:04 PM CDT <------------------------- output Thu 10 Oct 2013 11:50:05 PM CDT unset -f output Thu 10 Oct 2013 11:50:05 PM CDT <========================= [1] | hello Thu 10 Oct 2013 11:50:05 PM CDT <------------------------- hello Thu 10 Oct 2013 11:50:05 PM CDT unset -f hello Thu 10 Oct 2013 11:50:05 PM CDT unset -f hello_getOptions Thu 10 Oct 2013 11:50:05 PM CDT <========================= [0] | main ---------------------------------------------------------------------- ====================================================================== Recursive execution of modules occurs only when the module you are executing is considered sibling of the last module executed in the chain of executed modules and they both have the same name. The fact that no variable name is printed out in <> means that they were not created. The change in the arrows shown in the example, from +->+ to +~>+, means that module's related functions weren't exported for the new module execution either. It also means that the initialization script is reusing both module's related functions variables from the last module's environment in the chain of executed modules. In this case *random* module itself. Summary ~~~~~~~ This section has covered the module environment inside *centos-art.sh* script, including module types and possible combinations of them. The next section takes these concepts and focuses on the implementation of them. Once you finish it, you should be able of writing your own module environments from scratch inside *centos-art.sh* script. Module Implementation --------------------- Parent Modules ~~~~~~~~~~~~~~ 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. [[hello-simplest-directory-structure]] .Simplest directory structure of hello module. ====================================================================== ---------------------------------------------------------------------- . |-- 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/ | `-- hello.sh |-- Scripts/ <-- global functions are stored here. |-- centos-art.conf.sh <-- main configuration file. `-- centos-art.sh <-- main initialization file. ---------------------------------------------------------------------- ====================================================================== 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 lower. 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!" } ---------------------------------------------------------------------- ====================================================================== Child Modules ~~~~~~~~~~~~~ ... Sibling Modules ~~~~~~~~~~~~~~~ ... Recursive Modules ~~~~~~~~~~~~~~~~~ ... Summary ~~~~~~~ ... // vim: set syntax=asciidoc: