Syntax - Defining Commands

The syntax of a command is the definition of options, symbols and arguments that are accepted by commands. Each command defines its own syntax, allowing customization of flags and parameters, as well as defining order. The syntax is constructed using several different mechanisms, which when combined, allow for a great deal of control in restricting what is acceptable in the command line for a given command.

How it works

When you define a new command, you must give define a syntax bundle within a syntax extension point. When the plugin is loaded, the syntax bundle is parsed from the descriptor and loaded into the syntax manager. When the bundle is needed, when completing or when preparing for execution, the bundle is retrieved. Because a syntax bundle is immutable, it can be cached completely, and used concurrently.

Also, the help system uses the syntax to create usage statements and to map short & long flags to the description from an argument.

The puzzle pieces

See this document page for a concise description of the various syntax elements.

When setting out to define the syntax for a command, it is helpful to layout the synopsis and options that the command will need. The synopsis of a command can be used to define separate modes of operation. The syntax block itself is an implied <alternatives>, which means if parsing one fails, the next will be tried. To give an example of how breaking down a command into multiple synopsis can be helpful, we'll setup the syntax for a hypothetical 'config' command that allows listing, setting and clearing of some system configurations.

First, our synopsis...

    Lists all known configuration options and their values
config -l 

And our syntax...

<syntax alias="config">
  <empty />
  <option argLabel="list" shortName="l">
    <option argLabel="set" shortName="s">
    <argument argLabel="value">
  <option argLabel="clear" shortName="c">

To be continued...