Several uncommon but particularly useful PHP predefined variables

1. $php_errormsg — Previous error message

<?php
@strpos();
echo $php_errormsg;
?>

2. $http_response_header — HTTP response header

<?php
function get_contents() {
  file_get_contents("http://example.com");
  var_dump($http_response_header);
}
get_contents();
var_dump($http_response_header);
?>

3. $argc — Passed to Number of parameters of the script

<?php
var_dump($argc);
?>
当使用这个命令执行: php script.php arg1 arg2 arg3

4. $argv — Array of parameters passed to the script

<?php
var_dump($argv);
?>
当使用这个命令执行：php script.php arg1 arg2 arg3

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