w_scan: 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/w_scan - from package: w-scan

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

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