add-patch: 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/add-patch - from package: devscripts

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

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