apt-rdepends: 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/apt-rdepends - from package: apt-rdepends

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

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