The distinct interpretation of the $(),${} between make and shell

1) In make $() = ${}

To substitute a variable's value, write a dolar sign followed by the name of the variable in parentheses or braces:

either '$(foo)' or '${foo}' is a valid reference to the variable foo

2) In shell: $() != ${}

2.1) The '$' character introduces parameter expansion,command substitution, or arithmetic expansion.The

parameter name or symbol to be expanded may be enclosed in braces,which are optional but servo to

protect the variable to be expanded from characters immediately following it which could be interpreted

as part of the name

2.2 ) Command substitution allows the output of a command to replace the command itself ,

Command substitution occurs when a command is enclosed as follows:

$(command)

or

`command`