How to delete a variable in PHP

There are three ways to delete defined variables in PHP:

  • unset($var)
  • $var = (unset)$var
  • $var = null

Only the first of these ways actually deletes the variable completely. The other two, set it to NULL, which means that the variable no longer has a value, but in principle still exists. Accessing this would not generate the error “variable does not exist”.

Example: “unset($var)” vs “(unset)$var” vs “$var = null”

In this example the variables $var1, $var2 and $var3 are defined identically.


    // Defining sample variables
    $var1 = 'variable 1';
    $var2 = 'variable 2';
    $var3 = 'variable 3';
    // Output the three variables before deleting
    var_dump($var1, $var2, $var3);
    // Delete variables
    $var2 = (unset)$var2;
    $var3 = null;
    // Output variables after deleting
    // var1 should get an error because it was completely deleted
    var_dump($var1, $var2, $var3);
    // List all currently available variables


string(10) "variable 1"
string(10) "variable 2"
string(10) "variable 3"

Notice:  Undefined variable: var1 in [...][...] on line 17

array(6) {
  array(0) {
  array(0) {
  array(0) {
  array(0) {
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