scapy: 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 CentOS possible default full paths are:

/usr/bin/scapy - from package: scapy

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/scapy - from package: python-scapy

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

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