Like most Roo commands, the help and hint commands accept arguments. Arguments are additional parameters that are passed to a Roo command to customize command behaviour. For instance, the help command accepts a command argument and the hint command accepts a topic argument.

Earlier, we saw that the help command provides high-level details about commands supported by Spring Roo. The command argument is used to specify the name of the command for which detailed help information is needed, including information about required and optional arguments that can be passed to the Roo command. Similarly, the topic argument of hint command provides detailed information on a particular topic. The command and hint arguments are optional arguments; Roo shell doesn't force you to specify them.

In most cases Roo expects you to specify arguments in the following format:

--<argument-name> <argument-value>

To simplify using the hint and help commands, Roo lets you specify arguments without un-necessary frills. For instance, you can enter the help project command to get help information on the project command or you can enter the hint jpa command to get hints related to JPA.

The following output from the Roo shell shows the results from executing the help project and hint jpa commands:

roo> help project

Keyword:                   project
Description:               Creates a new project
 Keyword:                  ** default **
Keyword:                  topLevelPackage
   Help:                   The uppermost package name (this becomes the <groupId> in Maven and also the '~' value when using Roo's shell)
Mandatory:              true
.....

roo> hint jpa
Roo requires the installation of a JPA provider and associated database.

Type 'persistence setup' and then hit TAB three times.
.....

As you can see from the given output, the help command gives the exact details about a command. For instance, the help project command suggests that the project command accepts a mandatory argument named topLevelPackage. The hint jpa command provides high-level details about the jpa topic.

So, the question arises, how do you find the topics on which hints are available? Well, you can find these topics from Roo by executing the hint topics command, shown as follows:

roo> hint topics

The following hints are available to help you use Roo:
general, start, jpa, entities, fields, relationships,
controllers, finders, eclipse, logging
Just type 'hint topic_name' (without quotes) to view a specific hint.

The given output suggests that Spring Roo provides hints on the following topics: jpa, entities, fields, relationships, and so on.

The help and hint commands are the most often used commands; it is recommended that you should use them as and when required while working with your Roo project.

Let's say that you created an enterprise application using Spring Roo consisting of Spring Web MVC and Hibernate frameworks. Additionally, you executed Roo commands to add e-mail and JMS message sending support to some of the classes that you created as part of your enterprise application. Now, let's say a similar project needs to be created in your organization, which makes use of Spring Web MVC, Hibernate frameworks, and requires e-mail and JMS message sending functionalities. You can either re-execute all the Roo commands (that you used in your earlier enterprise application) to create the new enterprise application, or you can simply execute the Roo script from the earlier enterprise application.

When you execute a command from the Roo shell, it is recorded in a Roo script file, named log.roo. You will notice that a log.roo script file is created in the ch01-recipe directory. The log.roo script contains the commands that you executed using the Roo shell and also the details of when you started the Roo shell or exited it. This feature of Spring Roo can be useful if you want to review the commands that you executed or if you want to execute the same set of commands using the script command of Spring Roo. In a moment you will see how to execute a Roo script file, in the Creating application artifacts from Roo script recipe of this chapter.