Questions Ab Initio

 ${} substitution is similar to $ substitution except that the parameter must be preceded by curly brackets.  If we talk about these in parameter definitions then -     1. If the interpretation is $ substitution then we can give the value as both $ substitution and ${} substitution. e.g. Parameter can be of name $AI_SERIAL or ${AI_SERIAL}    2. If the interpretation is ${} substitution then we can only give the value as ${} substitution parameter. e.g. Parameter can only be of name ${AI_SERIAL}