ruby-standalone: 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/ruby-standalone - from package: ruby-standalone

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

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