Difference between $ and $$ Variables in PHP

$$var uses the value of the variable whose name is the value of $var.

It means $$var is known as refrence variable where as $var is normal variable.
It allows you to have a “variable’s variable” – the program can create the variable name the same way it can create any other string. .

Eg i

 <?php
  $name="Rajeev";
  $$name="Sanjeev";
  echo $name."<br/>";
  echo $$name."<br/>";
  echo $Rajeev;
 
 ?>

 Output :   Rajeev
    Sanjeev
    Sanjeev

In the above example
$name is just a variable with string value=”Rajeev”.
$$name is reference variable . $$name uses the value of the variable whose name is the value of $name.
echo $name print the value: rajeev

echo $$name print the value:Sanjeev \\ value of this($name) variable is act as reference of second variable($$name).

echo $rajeev print the value :Sanjeev \\ Here $rajeev is also act as reference variable.

Eg ii

 <?php
  $x = "100";
  $$x = 200;
  echo $x."<br/>";
  echo $$x."<br/>";
  echo "$100";
 
 ?>

 Output :  100
    200
    200

In the above example
You first assign the value of a variable, ($x) as the name of another variable.
When you set $x to a value, it will replace that variable name with the value of the variable you provide.
variable $x hold value = 100.
$$x(reference variable) hold value = 200. now we want to print the value.
echo $x gives output:100
echo $$x gives output:200.
echo $100 gives value.200. because it also act as a reference variable for value = 200.
Eg iii

 <?php
  $name="Rajeev";
  ${$name}="Sanjeev";
  echo $name."<br/>";
  echo ${$name}."<br/>";
                echo "$Rajeev"."<br/>";
 ?>

 Output:   Rajeev
    Sanjeev
                  Sanjeev
  

Eg iv

  <?php
 $name="Ravi";
 ${$name}="Ranjan";
 ${${$name}}="Rexx";
 echo $name;
 echo ${$name};
 echo ${${$name}};
  ?>

 Output : Ravi
    Ranjan
    Rexx
    

In the above example
variable $name hold value =”ravi”
variable ${ $name } hold value =”Ranjan” // it also declare like ${Ravi}.
variable ${$ {$name} } hold value =”Rexx” // it act as “variable’s of variable of variable” reference.
echo $name show output:ravi
echo ${ $name } show output:Ranjan.
echo ${ $ {$name} } show output :Rexx