aria-demo: 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/aria-demo - from package: libaria-demo

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

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