Variables and Parameter Passing

Both plans and components can declare variables that are used by their steps.

Component variables are evaluated and bound at the time the component is installed. Thus, if a step in a component control block refers to a component-scoped variable, the value used is the same as when the component was installed.

Plan variables, however, are evaluated and bound each time the plan is run. If a step in a plan refers to a plan variable, the value used is the value defined at the time the plan was run. Thus, the value might vary from one run to another.

A plan can declare both parameters and variables. The value of a variable is defined at the point of declaration based on the values of other variables and constants. A parameter is a special kind of variable whose value is defined by the caller. In the case of a top-level plan, the caller is the user who initiates the plan run. For each parameter that is declared by the plan, the user specifies the value for that parameter before running the plan. When a plan is invoked as the result of an <execSubplan> call, the plan that contains the call must explicitly pass values for each parameter that is declared by the called plan.

The <install>, <uninstall>, <snapshot>, and <control> blocks can declare parameters and local variables. As with plans, local variable values are locally defined, while parameter values are defined based on the values passed by the caller of the block. Both types of values can vary each time a plan is run.

You cannot reassign the value of a variable or parameter.