qrcode: 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 CentOS possible default full paths are:

/usr/bin/qrcode - from package: python-qrcode

You may install the required package with command yum install {package}

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