extend: 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/extend - from package: survex

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

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