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php – Override $argv for getopt

Posted by: admin July 12, 2020 Leave a comment

Questions:

example.php:

$args = __FILE__.' -vvv';
$argv = explode(' ', $args);
$argc = count($argv);
$GLOBALS['argv'] = $_SERVER['argv'] = $argv;
$GLOBALS['argc'] = $_SERVER['argc'] = $argc;

var_export(getopt('v'));

$ example.php -v

> array(‘v’ => false);

Eventually getopt does not look up to $GLOBALS to get argv. So it there any way I can override argv array?

How to&Answers:

TL;DR

No, there is no native way to do this. Depending of your goals there may be other ways to resolve the issue, but overriding is not one of them.

Operating on super-globals

Structure

To realize why it is so, you should know, that super-globals are not just "variables" to which you are referring. That means, if you are using $argv to de-reference arguments list, it does not mean that you’ll access some data which is stored in "variable" $argv. Instead, you’ll access to data container by "link", called $argv. However, there are different ways to access this data – $_SERVER['argv'] or $GLOBALS array at least. To illustrate, I’ll go with the code:

var_dump($argv, $_SERVER['argv']);
unset($argv);
var_dump($argv, $_SERVER['argv']);

This will result in something like:

array(2) {
  [0]=>
  string(11) "example.php"
  [1]=>
  string(4) "-vvv"
}//<--------------------- derived from $argv
array(2) {
  [0]=>
  string(11) "example.php"
  [1]=>
  string(4) "-vvv"
}//<--------------------- derived from $_SERVER['argv']
NULL//<------------------ we've unset $argv, so unset a reference
array(2) {
  [0]=>
  string(11) "example.php"
  [1]=>
  string(4) "-vvv"
}//<--------------------- but data is still there and available via another reference

Internally

As you can see, the reference can be destroyed, but actual data will remain untouched. That will be stored in symbols table. Many PHP functions are accessing this structure to retrieve data, and getopt() is not an exception. So the conclusion is – yes, you can modify the reference (or even destroy it), but actual data will be still in super-globals.

getopt()

Now, about this function. Just take a look at its implementation:

/* Get argv from the global symbol table. We calculate argc ourselves
 * in order to be on the safe side, even though it is also available
 * from the symbol table. */
if (PG(http_globals)[TRACK_VARS_SERVER] &&
    (zend_hash_find(HASH_OF(PG(http_globals)[TRACK_VARS_SERVER]), "argv", sizeof("argv"), (void **) &args) != FAILURE ||
    zend_hash_find(&EG(symbol_table), "argv", sizeof("argv"), (void **) &args) != FAILURE) && Z_TYPE_PP(args) == IS_ARRAY
) 
{
    //...omitted
}

It’s clearly stated, that it will try to search "argv" in symbol_table (if you want – here’s a link to – how it will be done exactly). And that means – it will access actual data, thus, overriding it externally will have no effect.

As a result – getopt() will work with data which were gathered at script startup, and that data will contain actual parameters, no matter if you’ll override them inside your script.