dpkg-vendor: 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/dpkg-vendor - from package: dpkg-dev

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

On Debian possible default full paths are:

/usr/bin/dpkg-vendor - from package: dpkg-dev

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

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