Hi, I'm learning to use the terminal. Is the "file" command not available?

"master@ubuntu:~$ ls
aplicativos meu_arquivo
master@ubuntu:~$ mv meu_arquivo meu_arquivo.txt
master@ubuntu:~$ ls
aplicativos meu_arquivo.txt
master@ubuntu:~$ cat meu_arquivo.txt
master@ubuntu:~$ echo "Exibindo mensagem na tela"
Exibindo mensagem na tela
master@ubuntu:~$ echo Escrevendo no arquivo > meu_arquivo.txt
master@ubuntu:~$ cat meu_arquivo.txt
Escrevendo no arquivo
master@ubuntu:~$ file meu_arquivo.txt
bash: file: command not found
master@ubuntu:~$ apt upgrade
E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?"