filterdiff: 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/filterdiff - from package: patchutils

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

On Debian possible default full paths are:

/usr/bin/filterdiff - from package: patchutils

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

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