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| @COMMANDS@ - inserts the list of commands available to the application. The runtime builds that list via introspection looking for classes that implement the Command interface. | | @COMMANDS@ - inserts the list of commands available to the application. The runtime builds that list via introspection looking for classes that implement the Command interface. |
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| =Implementing a Command=
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| Implement the <tt>[https://github.com/NovaOrdis/clad/blob/master/src/main/java/io/novaordis/clad/command/Command.java Command]</tt> interface or extend <tt>[https://github.com/NovaOrdis/clad/blob/master/src/main/java/io/novaordis/clad/command/CommandBase.java CommandBase]</tt> (recommended).
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| The implementation class must be named <tt><command-name>Command</tt>.
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| Example: <tt>PrintCommand</tt> will be matched to the "<tt>print</tt>" command. <tt>BusinessScenarioCommand</tt> will be matched to the "<tt>business-scenario</tt>" command.
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| ==Relationship between Command and ApplicationRuntime==
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| If a specific command does not need an application runtime instance (thus the framework is not required to instantiate an application runtime for it), the <tt>Command.needsRuntime()</tt> implementation must return <tt>false</tt>. By default <tt>CommandBase.needsRuntime()</tt> returns <tt>true</tt>.
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| ==In-Line Command Help==
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| If a text file named <tt><command-name>.txt</tt> is placed in the same package as the command implementation class, the framework will send the content of the file to <tt>stdout</tt> when in-line command help is requested:
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| <pre>
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| <wrapper> help|--help|-h <command>
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| </pre>
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| For a command whose name is <tt>blue</tt>, the in-line command help file should be named <tt>blue.txt</tt>.
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| For a command whose name is <tt>business-scenario</tt>, the in-line command help file should be named <tt>business-scenario.txt</tt>.
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| The length of a text line should not be larger than 99.
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| ==Command Options==
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| To declare that a command requires a specific option, override <tt>Command.requiredOptions()</tt>.
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| To declare that a command accepts a specific option, override <tt>Command.optionalOptions()</tt>.
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| In both cases, the set should contain option definitions only, the command instance is not expected to maintain any state inside the option instances, they can be recreated on each invocation. Example:
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| <pre>
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| @Override
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| public Set<Option> optionalOptions() {
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| return new HashSet<>(Collections.singletonList(new BooleanOption("ignore-faults")));
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| }
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| </pre>
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| Implementation Examples:
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| <blockquote style="background-color: AliceBlue; border: solid thin LightSteelBlue;">
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| :https://github.com/NovaOrdis/esa/blob/master/src/main/java/io/novaordis/esa/extensions/bscenarios/BusinessScenarioCommand.java<br>
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| </blockquote>
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| ==Default Command==
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| If no command is specified, the framework will use the “default command”, if there is one. If not, the application should display:
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| [error]: no command specified on command line and no default command was configured.
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| </pre>
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| <font color=red>
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| Instructions on how to configure the default command.
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| </font>
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| ==Command Execution==
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| <tt>execute()</tt> will be called on the main thread.
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| ==Universal Commands==
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| The framework comes with a set of universal commands that are available to any application:
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| ===Version and Release Date===
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| The framework supports the "<tt>version</tt>" command by default. The "<tt>version</tt>" command pulls version and release date from the underlying application and displays it in a standard format:
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| <pre>
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| version 1.0
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| release date 01/26/16
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| </pre>
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| =Error Handling= | | =Error Handling= |
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| If a processing error is caused by what the user did, or by the input data, and it can be corrected by user input (or by data correction), throw an UserErrorException with a human-readable message. The upmost runtime layer must be designed so it displays the error message at stderr and System.exit()s. | | If a processing error is caused by what the user did, or by the input data, and it can be corrected by user input (or by data correction), throw an UserErrorException with a human-readable message. The upmost runtime layer must be designed so it displays the error message at stderr and System.exit()s. |
Internal
Overview
The framework scans the command line looking for the first argument that can be mapped to a command.
The mapping process involves scanning the classpath and looking for classes implementing the Command interface. The current version does not introspect all classes, but just those whose simple class name match the following pattern: <commandName>Command.
All arguments between the wrapper name and the command name are interpreted as global options.
All arguments following the command name are interpreted as command options.
wrapper [global-options] command [command-options]
Subjects
- Concepts
- How to Implement a Command Line Application
Configuration File
Each command line option has a configuration file correspondent. Command line value takes precedence over the configuration file value.
In-line Application Help
If a text file named <application-name>.txt is placed in the same package as the ApplicationRuntime implementation class, its content is rendered to stdout every time the in-line application help is invoked with no-argument "help" command:
<app-name> help|--help|-h
The length of a text line should not be larger than 99.
Macros
The help renderer recognizes several macros, which are replaced by dynamically generated content at runtime.
@COMMANDS@ - inserts the list of commands available to the application. The runtime builds that list via introspection looking for classes that implement the Command interface.
Error Handling
If a processing error is caused by what the user did, or by the input data, and it can be corrected by user input (or by data correction), throw an UserErrorException with a human-readable message. The upmost runtime layer must be designed so it displays the error message at stderr and System.exit()s.