looper: command not found

Have You tried accessing the binary with the full path?

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/looper - from package: ladr4-apps

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