Execute shell commands in PHP

/**
Method to execute a command in the terminal
Uses :

1. system
2. passthru
3. exec
4. shell_exec

 */
function terminal($command)
{
    //system
    if (function_exists('system')) {
        ob_start();
        system($command, $return_var);
        $output = ob_get_contents();
        ob_end_clean();
    } //passthru
    else if (function_exists('passthru')) {
        ob_start();
        passthru($command, $return_var);
        $output = ob_get_contents();
        ob_end_clean();
    } //exec
    else if (function_exists('exec')) {
        exec($command, $output, $return_var);
        $output = implode("\n", $output);
    } //shell_exec
    else if (function_exists('shell_exec')) {
        $output = shell_exec($command);
    } else {
        $output = 'Command execution not possible on this system';
        $return_var = 1;
    }

    return array('output' => $output, 'status' => $return_var);
}

Use as this way:
$o = terminal('ls');
print_r($o);

http://www.binarytides.com/execute-shell-commands-php/