function_exists

Supported Versions: PHP 4, PHP 5, PHP 7, PHP 8
Return true if the given function has been defined
function_exists(string $function): bool
        $input = (defined('STDIN') ? STDIN fopen('php://input''r+'));



        if (
$isTtySupported === null && function_exists('proc_open')) {

            
$isTtySupported = (bool) @proc_open('echo 1 >/dev/null', [['file''/dev/tty''r'], ['file''/dev/tty''w'], ['file''/dev/tty''w']], $pipes);

        }
        }




        if (! 
function_exists('exec')) {

            return 
false;

        }
    private function hasVt100Support(): bool

    
{

        return 
function_exists('sapi_windows_vt100_support') && sapi_windows_vt100_support(fopen('php://stdout''w'));

    }
    private function readFromProcess(string $command): ?string

    
{

        if (! 
function_exists('proc_open')) {

            return 
null;

        }