get-oui: 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/sbin/get-oui - from package: arp-scan

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

On Debian possible default full paths are:

/usr/bin/get-oui - from package: arp-scan

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

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