PHP - How to know if server allows shell_exec

Question

On some servers, PHP is not allowed to run shell commands via shell_exec. How can I detect if current server allows running shell commands via PHP or not? How can I enable shell commands execution via PHP?

Answer 1

First check that it's callable and then that it's not disabled:

is_callable('shell_exec') && false === stripos(ini_get('disable_functions'), 'shell_exec');

This general approach works for any built in function, so you can genericize it:

function isEnabled($func) {
    return is_callable($func) && false === stripos(ini_get('disable_functions'), $func);
}
if (isEnabled('shell_exec')) {
    shell_exec('echo "hello world"');
}

Note to use stripos, because PHP function names are case insensitive.