Understanding Modules

=====================

Alain Reguera Delgado <al@centos.org.cu>

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 <<debug-parent-modules>>, 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

----------------------------------------------------------------------

======================================================================

<<debug-parent-modules>> 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>>.

[[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 <<debug-child-modules>> 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 <<debug-sibling-modules>>.

In <<debug-sibling-modules>>, 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

----------------------------------------------------------------------

======================================================================

<<debug-sibling-modules>> 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 <<debug-recursive-modules>>.

[CAUTION]

When you execute modules recursively, you should be very careful not

to get trapped into an endless loop.

In <<debug-recursive-modules>>, 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 <<debug-recursive-modules>>

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 <<hello-simplest-directory-structure>>, 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>>.

[[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 <al@centos.org.cu>, 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: