Code - Expansion

About

Expansion is just a transformation (replacement, …) applied to a syntax.

Code is replaced / injected at runtime.

An expansion is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to a replacement output sequence (also often a sequence of characters) according to a defined procedure.

The mapping process that transforms the input as into the output is known as expansion.

This is often used in template.

Example

Expansion of the environment variable

With the following USER environment variable

export USER=Foo

• The below env file

USER=$USER

• would become at runtime

USER=Foo