vw: command not found

Have You tried accessing the binary with the full path?

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/vw - from package: vowpal-wabbit

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