a56: 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/a56 - from package: a56

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

Error in other languages:
a56: bevel nie gevind nie
a56: comandă negăsită
a56: comando não encontrado
a56: commande introuvable
a56: command not found
a56: käsku ei ole
a56: không tìm thấy lệnh
a56: komanda nerasta
a56: Kommando nicht gefunden.
a56: kommandot finns inte
a56: komut yok
a56: nie znaleziono polecenia
a56: níor aimsíodh an t-ordú
a56: no se encontró la orden
a56: no s'ha trobat l'ordre
a56: opdracht niet gevonden
a56: parancs nem található
a56: perintah tidak ditemukan
a56: príkaz nenájdený
a56: příkaz nenalezen
a56: команда не найдена
a56: командата не е открита
a56: 命令找不到
a56: コマンドが見つかりません