handbrake: 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/handbrake - from package: handbrake

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

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