Unset all variables in PHP script

Question

Trying to unset automatically all variables in script.

Have tried this way:

  echo '<br /> Variables in Script before unset(): <br />';
  print_r(array_keys(get_defined_vars()));
  echo '<br /><br />';
  var_dump(get_defined_vars());

  // Creates string of comma-separated variables(*) for unset.
  $all_vars = implode(', $', array_keys(get_defined_vars()));

  echo '<br /><br />';
  echo '<br />List Variables in Script: <br />';
  echo $all_vars;
  unset($all_vars);

  echo '<br /><br />';
  echo '<br />Variables in Script after unset(): <br />';
  print_r(array_keys(get_defined_vars()));
  echo '<br />';
  var_dump(get_defined_vars());

Why does it not work?

Is there a better way to do this?

Thanks for helping!

(*) It's seems somewhat that it does not really create the variables, but a string that looks like variables...

There isn't much reason to unset all variables. Memory management in php is like C or C++ where allocated memory needs to be freed. PHP will free all used memory automatically after the script is executed. — David Corbin, Oct 08 '14 at 02:05
Just for anyone's knowledge: the reason I'm doing it is because our system is coded fairly poorly and we must include() file after file for a "report mailing" routine where we pretend we've run a report by giving them the $_POST they expect. Since it's an include, variables are stuffed into the global scope and we should clean them up before loading another (unrelated) report. I'm interested in others' use cases for this code. — Vael Victus, Jan 22 '15 at 18:15

airtech · Accepted Answer · 2014-10-08T02:25:22.593

18

Here ya go ->

$vars = array_keys(get_defined_vars());
for ($i = 0; $i < sizeOf($vars); $i++) {
    unset($$vars[$i]);
}
unset($vars,$i);

And to clarify, implode returns "a string representation of all the array elements in the same order". http://php.net/manual/en/function.implode.php

Unset requires the actual variable as a parameter, not just a string representation. Which is similiar to what get_defined_vars() returns (not the actual variable reference). So the code goes through the array of strings, and returns each as a reference using the extra $ in front - which unset can use.

edited Oct 08 '14 at 02:25

answered Oct 08 '14 at 01:52

airtech

486
3
12

This doesn't work for me. I don't think $vars gets assigned by reference. Aren't you just unsetting the copy in the vars variable while leaving the original untouched? – ThatOneDude Oct 08 '14 at 02:09
There ya go - it's corrected. Sorry, I thought I had it working (something was working - just not sure what) :) – airtech Oct 08 '14 at 02:17
Ash501, just an FYI - that code snippet does not work. – airtech Oct 08 '14 at 02:19
@airtech - Yes you're right, yours works now -Thanks! was trying to avoid the loop. Left me wondering why mine does not work...? – Ash501 Oct 08 '14 at 02:22
I updated your code to skip the $i variable, as it was getting included in the unset and thereby looping forever! :} – Vael Victus Jan 22 '15 at 18:50
use `foreach` instead of `for` in `php 7` – Adarsh Madrecha Jan 15 '18 at 11:26

score 7 · Answer 2 · answered Aug 31 '17 at 15:50

7

don't know about you guys, but $$vars doesn't work for me.

that's how I did it.

$vars = array_keys(get_defined_vars());
foreach($vars as $var) {
    unset(${"$var"});
}

answered Aug 31 '17 at 15:50

Leoncio

1,479
2
16
19

score 3 · Answer 3 · answered Jul 09 '16 at 06:43

3

foreach (array_keys($GLOBALS) as $k) unset($$k); unset($k);

answered Jul 09 '16 at 06:43

ferhad

41
1

2

**Just a note:** This must be run in the global scope - using this in function will throw errors! Better to use `unset($GLOBALS[$k])` instead of `unset($k)`. – Sep 14 '17 at 19:05

score -1 · Answer 4 · answered Jan 10 '20 at 19:47

I couldn't run @airtech's answer on my PHP 7.0 instance. It throws an array to string conversion error.

This updated/simplified version of his solution works for me (I also added curly braces "{ }" for more clarity):

foreach(array_keys(get_defined_vars()) as $strVarName){
  unset(${$strVarName});
}

To answer the original question, as others stated, implode would just create a string of what looks like variables but wouldn't be interpreted as such by PHP.

The code solving the issue makes use of the "variable variables" concept in PHP. More on this concept here: https://www.php.net/manual/en/language.variables.variable.php

Unset all variables in PHP script

4 Answers4

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