In PDI, you can define and use variables, just as you do when you code in any computer language. We already defined a couple of variables when we created the kettle.properties file in Chapter 1, Getting Started with PDI. Now, we will see where and how to use them.
It's simple: any time you see a dollar sign by the side of a textbox, you can use a variable:
Sample textboxes that allow variables
You can reference a variable by enclosing its name in curly braces, preceded by a dollar sign (for example, ${INPUT_FOLDER}).
A less used notation for a variable is as follows: %%<variable name>%% (for example, %%INPUT_FOLDER%% ...
