php call_user_func variable error

Pay attention to the signature of call_user_func and call_user_func_array.

function product($a, $b) {
  echo "Yo ".$a;
  echo "Yo ".$b;
  echo "<br>\n";
}

// there are 3 single arguments
call_user_func('product', 'dd', 'lizzy');

// the same with variables
$fn_name = 'product';
$arg1    = 'dd';
$arg2    = 'lizzy';

call_user_func($fn_name, $arg1, $arg2);

// or give ARGUMENS ONLY as array, but function name as string scalar
$args    = array($arg1, $arg2);
call_user_func_array($fn_name, $args);

// if you for some reason need to handle a single array for the name and arguments in one,
// you need to write your own function:
function call_user_func_array2($call_info)
{
  $fn_name = array_shift($call_info);  //extract first item
  call_user_func_array($fn_name, $call_info);
}

$call_info = array($fn_name, $arg1, $arg2);
call_user_func_array2($call_info);

In addition we can extend the code above to process on a given string "'product','dd','lizzy'". (e.g. in situations when it is stored in this form in some database)

You first need to extract the comma separated values in this string. You can achieve this by str_getcsv or more flexible by a regular expression. Let's say it is separated by comma with optional whitespaces and enclosed in single or double qoutes. The regex could look like: (?:^|,)\s*(['"])(.+?)\1\s*?(?=,|$). The 2nd subpatter (.+?) will capture everything inside the single/double quotes.

Combined with call_user_func_array2 it looks like that:

function call_user_func_string($call_info)
{
  if(!preg_match_all('~(?:^|,)\s*([\'"])(.+?)\1\s*?(?=,|$)~u', $call_info, $matches))
    throw new Exception("call_user_func_string expects parameter 1 to be a string like `'functionname','arg1','arg2' [,...]` "
                      . 'or `"functionname","arg1","arg2" [,...]`.');

  call_user_func_array(array_shift($matches[2]), $matches[2]);
}


// some differently formatted examples

$my_string = "'product','dd','lizzy'";
call_user_func_string($my_string);

$my_string = '  "product"  ,  "dd"  ,  "lizzy"  ';
call_user_func_string($my_string);

$my_string = <<<'_END_'
    'product'   ,   "dd",'lizzy'    ,"lucy's cat"   
_END_;

call_user_func_string($my_string);