All the variables that we described in the previous sections can be defined thanks to 2 possible syntaxes which are ${variable-name} or ${variable-name:default-value}. The first syntax doesn't define any default value so if the variable has not be set the value will be ${variable-name} to indicate that it could not be resolved. The second syntax allows you to define the default value after the semi colon so if the variable has not be set the value will be the given default value.