poly: 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/poly - from package: polyml

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

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