What is Variable Expansion in Bash ?

About

variable expansion is an expansion that replaces a variable expression by its value.

Example

Prerequisite: We set the value of the variable foo to bar to perform the expansion

foo=bar 

Example:

• In the following expression that is composed of:
  • the echo command
  • and a variable expression foo

echo ${foo}

• The variable expression foo will be replaced / expanded by the value bar at runtime resulting to

echo bar

that outputs to the console

bar