rat: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/rat - from package: rat

You may install the required package with command apt-get install {package}

Error in other languages:
rat: bevel nie gevind nie
rat: comandă negăsită
rat: comando não encontrado
rat: commande introuvable
rat: command not found
rat: käsku ei ole
rat: không tìm thấy lệnh
rat: komanda nerasta
rat: Kommando nicht gefunden.
rat: kommandot finns inte
rat: komut yok
rat: nie znaleziono polecenia
rat: níor aimsíodh an t-ordú
rat: no se encontró la orden
rat: no s'ha trobat l'ordre
rat: opdracht niet gevonden
rat: parancs nem található
rat: perintah tidak ditemukan
rat: príkaz nenájdený
rat: příkaz nenalezen
rat: команда не найдена
rat: командата не е открита
rat: 命令找不到
rat: コマンドが見つかりません