gbp: 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/gbp - from package: git-buildpackage

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

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