diffstat: 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/diffstat - from package: diffstat

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

On Debian possible default full paths are:

/usr/bin/diffstat - from package: diffstat

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

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