radiff2: 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/radiff2 - from package: radare2

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

Error in other languages:
radiff2: bevel nie gevind nie
radiff2: comandă negăsită
radiff2: comando não encontrado
radiff2: commande introuvable
radiff2: command not found
radiff2: käsku ei ole
radiff2: không tìm thấy lệnh
radiff2: komanda nerasta
radiff2: Kommando nicht gefunden.
radiff2: kommandot finns inte
radiff2: komut yok
radiff2: nie znaleziono polecenia
radiff2: níor aimsíodh an t-ordú
radiff2: no se encontró la orden
radiff2: no s'ha trobat l'ordre
radiff2: opdracht niet gevonden
radiff2: parancs nem található
radiff2: perintah tidak ditemukan
radiff2: príkaz nenájdený
radiff2: příkaz nenalezen
radiff2: команда не найдена
radiff2: командата не е открита
radiff2: 命令找不到
radiff2: コマンドが見つかりません