Explain the difference between $message and $$message.

$message is used to store variable data. $$message can be used to store variable of a variable. Data stored in $message is fixed while data stored in $$message can be changed dynamically.

E.g. $var1 = 'Variable 1'

$$var1= 'variable2'

This can be interpreted as $ Variable 1='variable2';

For me to print value of both variables, I will write

$var1 $($var1)