Simple CLI Command using Symfony

SendSmsCommand.php

<?php
// this is the file structure of the command file.
// src/SmsBundle/Command/SendSmsCommand.php
namespace SmsBundle\Command;

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;
//we need this to take inputs from the console.
use Symfony\Component\Console\Input\InputArgument;

class SendSmsCommand extends Command {

    protected function configure() {
        $this

            // command name (the part after "app/console")
            ->setName('sms:send')
            // first input for phone number. 
            // This is mendetory input. Without this it will create error.
            ->addArgument('phone', InputArgument::REQUIRED, 'Phone number?')
            // second input for message. 
            // Notice that this argument is optional, which means, user can ignore this input
            ->addArgument('message', InputArgument::OPTIONAL, 'Short Message?')
            // the short description shown while running "php app/console list"
            ->setDescription('Sends a sms to the phone number.')
        ;
    }

    protected function execute(InputInterface $input, OutputInterface $output) {
        // get the input values using getArgument()
        $phoneNumber = $input->getArgument('phone');
        $shortMessage = $input->getArgument('message')

        // shows a message by adding a "\n"
        $output->writeln('Sending a SMS to the number -> ' . phoneNumber);
        //also you can send array of lines
        $output->writeln([
            '----##--------##----',
            '',
        ]);
        
        // ...
        // sms sending code
        // ...
        
        // shows a message without adding a "\n"
        $output->write('SMS Sent -> ' . phoneNumber . '. with a message: ' . $shortMessage);
    }

}
?>

There is lack of $ character on line 36. and 48.