How to clear some php variable (not all php variable) using PHP?

Question

How to clear some php variable (not all php variable) using PHP ?

i have many php variable

EG: $a,$b,$c,$d.$e,$f,$g,$h,$i,$j

i want to clear all php variable and not clear $a,$c,$d

i use this code but not work, how can i do ?

<?PHP
$a = "1";
$b = "2";
$c = "3";
$d = "4";
$e = "5";
$f = "6";
$g = "7";
$h = "8";
$i = "9";
$j = "10";
   $dontDelete = array('a' , 'c' , 'd');
   foreach ($ as $key=>$val)
       {
          if (!in_array($key,$dontDelete)) 
             {
               unset($[$key]);
             }
       }
?>

so let me get this straight... you want to clear variables that are not in that array, not keys in the array itself, right? — Ares Draguna
– Ares Draguna, Commented Oct 28, 2014 at 16:45
And you only want to destroy scalars, not arrays or objects, right? — Jonathan M
– Jonathan M, Commented Oct 28, 2014 at 16:49

BentCoder · Accepted Answer · 2014-10-28 17:40:53Z

3

$defined_variables = get_defined_vars();
$variables2keep = array("a", "b", "c", "variables2keep");

foreach ($defined_variables as $variable => $value) {
    if (! in_array($variable, $variables2keep)) {
        unset($$variable);
    }
}

Demo

edited Oct 28, 2014 at 17:40

BentCoder

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answered Oct 28, 2014 at 16:49

Ali

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4 Comments

Ali Over a year ago

Yes, save the variables that you want to keep inside the exclusion array.

Jonathan M Over a year ago

It's because you're even clearning the $variables2keep. I fixed it for you.

RiggsFolly Over a year ago

Be carefull with this solution It will remove EVERYTHING from the GLOBAL Scope, including the a,b and c variables that are supposed to be kept. Not what I think (s)he wants. Did you test this code?

ʰᵈˑ Over a year ago

As @RiggsFolly has said, this is a very risky approach. I've created an alternative that is much safer

theblackwidower · Accepted Answer · 2014-10-28 16:49:28Z

0

I think the main reason it won't work is because you can't reference variable names in that way. If those names were merely indexes in a single associative array, it might work. Otherwise, I suggest you simply list all variables, and manually unset them.

answered Oct 28, 2014 at 16:49

theblackwidower

411 silver badge7 bronze badges

Comments

Community · Accepted Answer · 2017-05-23 12:27:22Z

I know you've accepted an answer, but it's a very risky approach. Here's an alternative that won't destroy all superglobals and other non-intended variables to delete.

Grab all the variables named with 1 letter from the file
Loop through them
Check if they're in the whitelist
If not in whitelist, kill them.

$arrWhitelist = array("a", "b", "c");
$file = file_get_contents(__FILE__);
preg_match_all('/\$[A-Za-z_]{1}/', $file, $vars);

foreach($vars[0] as $variables) {
    $variables = ltrim($variables, "$");
    if(in_array($variables, $arrWhitelist) == FALSE ) {
        unset($$variables);
    }
}

For example;

<?php
ini_set('display_errors', 1);
error_reporting(E_ALL);

$a = "1";
$b = "2";
$c = "3";
$d = "4";
$e = "5";
$f = "6";
$g = "7";
$h = "8";
$i = "9";
$j = "10";

$arrWhitelist = array("a", "b", "c");
$file = file_get_contents(__FILE__);
preg_match_all('/\$[A-Za-z_]{1}/', $file, $vars);

foreach($vars[0] as $variables) {
    $variables = ltrim($variables, "$");
    if(in_array($variables, $arrWhitelist) == FALSE ) {
        unset($$variables);
    }
}

echo $a; //Output: 1
echo $g; //Ouput: Notice: Undefined variable: g in C:\xampp\htdocs\test.php on line 29

Ares Draguna · Accepted Answer · 2014-10-28 16:56:05Z

This is the only way I see that could fit your needs. In this example, $d, $e and $f are the variables that will be "deleted"

$a = "1";
$b = "2";
$c = "3";
$d = "4";
$e = "5";
$f = "6";
$g = "7";
$h = "8";
$i = "9";
$j = "10";

$delete = array('d', 'e', 'f');


foreach($delete as $yes){
    switch($yes){
        case 'a':
            $a = 0;
            break;
        case 'b':
            $b = 0;
            break;
        case 'c':
            $c = 0;
            break;
        case 'd':
            $d = 0;
            break;
        case 'e':
            $e = 0;
            break;
        case 'f':
            $f = 0;
            break;
        case 'g':
            $g = 0;
            break;
        case 'h':
            $h = 0;
            break;
        case 'i':
            $i = 0;
            break;
        case 'j':
            $j = 0;
            break;
    }
}

echo $d . ' ' . $e . ' ' . $f;

at echo you will see that $d, $e and $f will be 0. Switch to null if that is what you want.

Hope it helps!

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