qrencode: 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/qrencode - from package: qrencode

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

On Debian possible default full paths are:

/usr/bin/qrencode - from package: qrencode

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

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