$$abc=”xyz”;
$xyz=5;

<?php
Echo $$abc; // this will display 5
Echo ${$abc} //another way of interpreting the same thing

<?php
$expected = array('name', 'email', 'comments');
$required = array('name', 'comments');
$missing = array();
foreach ($_POST as $key => $value) {
  // assign to temporary variable and strip whitespace if not an array
  $temp = is_array($value) ? $value : trim($value);
  // if empty and required, add to $missing array
  if (empty($temp) && in_array($key, $required)) {
    $missing[] = $key;
  } elseif (in_array($key, $expected)) {
    // otherwise, assign to a variable of the same name as $key
    ${$key} = $temp;
  }
}
?>

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