unlambda: 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/unlambda - from package: unlambda

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

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