qr: 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/qr - from package: python-qrcode

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

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