mrbc: 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/mrbc - from package: mruby

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

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